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Integrated General
Biology
A Contextualized Approach
Active Learning Activities
FIRST EDITION
Jason E. Banks
Julianna L. Johns
Diane K. Vorbroker, PhD
Genetics and Meiosis
Active Learning Activities
Chapter 9 Genetics and Meiosis
Section 9.1 Becoming Mendel
Directions for
the Student:
This lesson is designed for you to complete, on your own or in your study group. Use
your notes and follow along in the text, as you find necessary.
Objectives:
1.
2.
3.
4.
Identify the contributions of Gregor Mendel
Determine genotypes and phenotypes in genetic crosses.
Calculate probabilities for genetic outcomes.
Practice Punnett squares for monohybrid and dihybrid crosses of simple
dominant/recessive traits
When Gregor Mendel was alive, biology as we know it was a new field. The causes of human conditions
and inheritance were based on theories and in many cases the teachings of the Church. By the time
Mendel was in college, good science and the scientific method were becoming accepted and expected.
Mendel’s experiments were the first to exhaustively study patterns of inheritance.
When Gregor Mendel was alive, biology as we know it was a new field. The causes of human conditions
and inheritance were based on theories and in many cases the teachings of the Church. By the time
Mendel was in college, good science and the scientific method were becoming accepted and expected.
Mendel’s experiments were the first to exhaustively study patterns of inheritance.
1. Answer these question about Mendel's plan.
What problem or question did Mendel How are traits transmitted from parents to offspring.
identify?
What training, expertise, and
Mendel grew up on a farm helping his father, and learned
personality traits did Mendel have
skills like breeding and grafting plants and trees. Then in high
that helped him to do his experiment? school and college he studied math and science and learned
strong critical thinking skills and good experimental
technique. Joining a monastery was especially important so
that Mendel would have the time and tools he needed to
carry out his experiments. Finally, Mendel had a strong will,
showing great persistence and attention to detail.
Explain in some detail how and where Mendel performed his experiments over about 8 years in the
Mendel did his experiment.
gardens of a monastery in Austria. He used garden peas as
his model organism, studying seven distinct traits individually
and in combination with each other over at least 2
generations. It is estimated he grew over 10,000 plants.
Becoming Mendel
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Genetics and Meiosis
Active Learning Activities
Pea plants (Pisum sativum) are easy to work with in the garden and have several traits, or phenotypes,
that are easy to observe. Let’s consider one of the easiest to see: tall-stemmed vs short-stemmed plants.
Pea plants are either tall or short, there is no in between like in humans, and the difference in height is
obvious.
Pea plants self-fertilize, but Mendel was able to control which plants mated with each other by
removing the pollen stems and using small paint brushes to control which plants were mated. This is
called a genetic cross, mating organisms with variations in a trait to observe how that ONE trait is passed
on (inherited). Here is the result of his mating of plants of different heights.
Phenotype of Parents crossed:
Tall plant x Short plant
Phenotypes in offspring:
957 Tall, 0 Short
2. Summarize this data.
The parents are known as the P generation. What letter(s) F1 or F1
can be used to represent the first generation of offspring?
the allele for Tall is masking (dominant
over) the allele for short
Why were all the offspring Tall?
Mendel wanted to see if the short phenotype could “reappear.” For his next experiment, he decided to
cross two plants from the first generation (offspring from above).
Cross F1 x F1:
Tall x Tall
Phenotype of second
generation offspring:
787 Tall, 277 Short
3. Both Tall and short plants grew. How did this happen?
What letter(s) can be used to represent the second F2 or F2
generation of offspring?
What percentage of the second generation is
short?
26 %
What percentage of the second generation is Tall? 74%
Mendel’s hypothesis was that a phenotype is a combination of “particles,” one from each parent. Each
parent contributes one of the two particles at fertilization. Therefore, each individual has two copies of
that trait, one they got from their mother, and one they got from their father. But in many cases, one of
the “particles” is more prominent, or “stronger” than the other. Having one trait stronger than the other
meant Mendel was able to observe that in some cases traits he believed to present did not express
themselves.
Becoming Mendel
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Genetics and Meiosis
Active Learning Activities
4. Apply your understanding of trait expression to the following questions.
Which phenotype is dominant, Tall or short? What
generation proves which trait is dominant?
Tall is dominant; it is the only trait in the
F1 generation
What term describes the “non-dominant” trait?
recessive
Tall and short are variations of one gene that produces a
protein that determines the length of the plant’s stem.
What is the technical term for variations of a gene?
alleles
Consider the phenotypes as a combination of two particles, like Mendel hypothesized, and work
through the cross again:
5. Answer the following questions about passing on traits from parents to offspring.
What cell types join together at fertilization?
eggs and sperm
What phenotype are the F1?
all Tall
Can the F1 be anything other than Tall+short? Why No- one parent can ONLY contribute Tall, the other
or why not?
parent can Only contribute short
What term is used to describe an individual that
has two different alleles?
heterozygote
What term is used to describe an individual that
has two of the same alleles?
homozygote
Plants are one of the easiest organisms to observe the expression of traits across multiple generations.
Let’s assign one plant as “male” and the other plant as “female.”
Becoming Mendel
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Genetics and Meiosis
Active Learning Activities
Mating is assumed to be random. In other words, each sperm has an equal chance of fertilizing each
egg.
6. Determine what combinations of sperm and egg the two F1 can produce:
If a sperm carrying the Tall allele fertilizes an egg
carrying the Tall allele, what alleles and phenotype
will that F2 individual have?
Tall+Tall, phenotype Tall
If a sperm carrying the Tall allele fertilizes an egg
Tall+ short, phenotype Tall
carrying the short allele, what alleles and phenotype
will that F2 individual have?
If a sperm carrying the short allele fertilizes an egg
carrying the Tall allele, what alleles and phenotype
will that F2 individual have?
short + Tall, phenotype Tall
If a sperm carrying the short allele fertilizes an egg
short + short, phenotype short
carrying the short allele, what alleles and phenotype
will that F2 individual have?
Theoretically, each of these fertilizations have an
equal chance of happening. There are four possible
combinations, but how many possible phenotypes
are there?
two, Tall and short
Therefore, for every four F2 that grow, how many
are expected to be Tall?
three out of four, ¾, 25%
The results of Mendel’s cross of Tall x short parents produced F1 that were all Tall; out of 1064 F2, 787
were Tall and 277 were short. That is approximately a 3 to 1 ratio of dominant to recessive, or 75%
dominant, 25% recessive in the F2 generation. He also experimented with six other traits, such as flower
color, pea color, pod shape and color, and all followed this pattern, with the data showing an
approximately 3 to 1 ratio of dominant to recessive traits in the F2 generation.
Becoming Mendel
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Genetics and Meiosis
Active Learning Activities
7. Test your understanding of Mendel’s work by answering the following questions.
State Mendel’s Law of Segregation in
your own words.
The alleles that an individual has (their genotype) separate
and are distributed to their offspring. Offspring receive one
allele from their mother and the other from their father.
Why wouldn’t Mendel have data exactly In theory there is an equal chance for sperm and egg to meet,
as predicted, with exactly a 3 to 1 ratio but in practice the ratio can vary. Probabilities tell us
of dominant to recessive in the F2
expected outcome, but chance can be unpredictable.
generation?
How did he control which plants were
mated to each other?
He removed the pistils (male parts) and used a paint brush to
put the pollen onto the stamen of the flowers he wanted to
use in the cross
What does true-breeding mean, and
why was it so important to have truebreeding plants in the P generation?
true-breeding means that the trait is always passed to the
offspring, or the parents can only make offspring like them.
It’s important because he needed to be sure that there was
only one type of particle in the parents to start the matings.
For simplicity, in a genetic cross the two alleles that an individual carries are usually represented as a
single letter.
REMEMBER: alleles are different versions of the same gene. THEREFORE ONE LETTER OF THE ALPHABET
REPRESENTS BOTH ALLELES, WRITTEN UPPERCASE FOR THE DOMINANT TRAIT AND LOWERCASE FOR
THE RECESSIVE TRAIT.
8. Let’s use the 20th letter of the English alphabet to represent the gene for pea plant height, and
apply that to the following questions.
Write the letter in the proper form to represent the
Tall allele
T (uppercase/big/capital T)
Write the letter in the proper form to represent the
short allele
t (lowercase/little/small t)
A phenotype is the appearance of a trait, but what
term is used to describe the genetic allele
combination that an individual has for that trait?
the genotype
Write the two letters that would represent a Tall F1
plant
Tt (big T, little t)
Becoming Mendel
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Genetics and Meiosis
Active Learning Activities
Hint: It can be helpful to choose a letter that looks very different when written uppercase or lowercase.
For example, “big U” and “little u” don’t look much different, especially in handwriting. But “big A” and
little a” do look different.
Now let’s write out the Tall x short crosses using letters instead of words:
True-breeding
(homozygous)
Parental generation
gametes contain
TT
(Tall)
tt
X
only T
only t
First generation (F1)
Tt
All are Tall
Mate F1 x F1
gametes contain
Second generation (F2)
Tall and short
(short)
Tt
X
Tt
T or t
TT, Tt, tt
Punnett squares are named after the mathematician (Reginald Punnett) that devised them to interpret
Mendel’s genetic crosses. A small table helps to organize the gametes of the parents and the possible
offspring.
9. Follow along step by step to draw a Punnett square for the F1 mating of two heterozygous Tall
plants. Parent 1 is Tt, and Parent 2 is Tt.
a. Fill in each of the Parent
Parent 1 Gametes
spaces for the gametes to
make headings for the
columns and rows.
T
t
b. Determine what gametes they
can produce: ½ T and ½ t
T
Tt
c. Match the gametes, across
TT
Parent 2
and down. So, if the big T from
Parent 1 joins with the big T
Gametes
from parent 2, that square will
t
Tt
tt
get TT.
Becoming Mendel
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Genetics and Meiosis
Active Learning Activities
10. Using the Punnett square you have just created, answer the following questions.
What fraction of the offspring (boxes) are predicted to get TT?
1/4
What fraction of the offspring (boxes) are predicted to get Tt?
2/4 or ½
What fraction of the offspring (boxes) are predicted to get tt?
1/4
What genotype(s) will produce Tall plants?
TT or Tt
What genotype(s) will produce short plants
tt
What fraction of the offspring (fraction of boxes) will be phenotype Tall?
3/4ths
Once you understand the basic principles of a simple dominant/recessive genetic cross, you can predict
the results of any mating.
11. Using the letter R, practice the terms used to describe the genotype of an individual. Remember a
genotype has two letters.
If an organism has the recessive trait (phenotype), what would its genotype be?
rr
If an organism has the dominant trait (phenotype) what could its genotype(s) be?
RR or Rr
A heterozygote would have the genotype:
Rr
12. Draw your own Punnett square for a mating that crosses two heterozygotes, using the letter R to
represent the gene.
Parent 1 Gametes
Parent 2
Gametes
R
r
R
RR
Rr
r
Rr
rr
The pattern will always be the same for the alleles from a cross between two heterozygotes: for a simple
dominant-recessive trait, the predicted outcome is ¼ homozygous dominant, ½ heterozygous (dominant
phenotype), and ¼ recessive (homozygous recessive).
Two traits at a time
Organisms don’t just have one trait, so Mendel’s next question was what happens when you track two
traits? Do they stay together, or can they be mixed up? For example, if a plant was Tall with Purple
Becoming Mendel
8
Genetics and Meiosis
Active Learning Activities
flowers (both dominant traits), and the other was short with white flowers (both recessive traits), would
those traits stay together, or could they be inherited independently?
13. Parents: Tall (TT) Purple (PP) x short (tt) white (pp)
What would the F1 phenotype be?
all Tall Purple
What is the genotype of the F1 plants (use letters)?
TtPp
The F1 are heterozygous for both genes- the one for stem height and the one for flower color. When the
F1 form gametes, do the alleles from the parents stay together (dominant + dominant or recessive +
recessive), or can the dominant allele of one gene be paired with the recessive allele of the other gene?
14. Consider the two scenarios and fill in the missing combinations:
F1:
Gametes:
If Parental alleles have to
stay together
If Parental alleles can be separated
Tall Purple short white
Tall short Purple white
Tall Purple
short white
Tall Purple
Tall white short white short white
15. In the first scenario, the two possible gametes would contain TP or tp. Fill in the Punnett square for
this cross:
Parent 1 Gametes
TP
Parent 2
Gametes
TP
tp
TTPP
TtPp
tp
TtPp
ttpp
16. Using the Punnett square you just made, answer the following questions.
What proportion of the F2 are predicted to be TTPP?
¼
What proportion of the F2 are predicted to be TTPP?
½
What proportion of the F2 are predicted to be TTPP?
¼
What proportion of the F2 are predicted to be tall and purple? ¾; 1/4
Short and white?
Becoming Mendel
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Genetics and Meiosis
Active Learning Activities
Therefore, if Mendel saw only two phenotypes in the F2, and they were the same phenotypes as the P
generation, that means the alleles from the parents had to stay together. But in his experiments,
Mendel got four (4) different phenotypes. That means the second scenario was taking place.
17. Use the Punnett square below to show the phenotypes Mendel was seeing.
Parent 1 Gametes
Tp
tP
TTPP
TTPp
TtPP
Tp
TTPp
TTpp
tP
TtPP
TP
TP
Parent 2
Gametes
TtPp
TtPp
tp
TtPp
Ttpp
tp
TtPp
Ttpp
ttPP
ttPp
ttPp
ttpp
18. Now compile the results of your Punnett square:
Genotype
T_ P_
Phenotype
tall
purple
# (out of 16)
9
T_ pp
ttP_
ttpp
tall
short
short
white
purple
white
3
3
1
In a classic dihybrid experiment, this pattern is always observed.
There is a saying in probability – “Chance has no memory.” A Punnett square does not predict the exact
order of things, only each individual event as it happens. For example, in humans there are two sex
chromosomes, an X and a Y. The mother always contributes an X, the father can contribute an X or a Y.
Theoretically, there is a 50:50 chance of a child being born male (XY) or female (XX).
19. Answer these questions to prove that chance has no memory.
If a couple’s first child is a girl, what are the chances that their next child will be a
girl?
½ or 50%
If a couple’s first child is a girl, what are the chances that their next child will be a
boy?
½ or 50%
If you flipped a coin 2 times, and the first is heads, what are the chances that the
second time will be heads?
50%
Becoming Mendel
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Genetics and Meiosis
Active Learning Activities
The same is true for genetic crosses. As long as the options (gametes) don’t change, the probability will
always stay the same for each mating.
Let’s try one last real-world application. Antoine and Alicia want to have children, but they are worried
about cystic fibrosis. Cystic fibrosis is a devastating recessive disease. Antoine’s brother died of cystic
fibrosis at the age of 22, and Antoine knows he is a carrier (heterozygote). Alicia’s baby sister is 4 years
old and was just diagnosed, so Alicia was tested and found out she also is a carrier.
20. Answer the following questions regarding the possibility of cystic fibrosis in Antoine and Alicia’s
possible children.
1. Using the letter F to represent the cystic fibrosis Ff
gene (known as CFTR), what genotype do Antoine
and Alicia have?
2. What genotype would you assign to their child if
it is born with cystic fibrosis? What is the chance
that they will have a child with the disease?
ff; 1 out of 4
3.
½ of their children are predicted to be
carriers (heterozygotes)
What is the chance that they will have a child
that is a carrier?
4. If they have four children, how many of them are Three
predicted to be free of the disease?
5. If their first child is born with cystic fibrosis, what 1 out of 4
are the chances that their second child will be
born with cystic fibrosis? (think carefully!)
6. If they have 5 children, could they ALL have cystic yes, there is ¼ chance each time. It would be
fibrosis? Why or why not?
very unlikely but technically possible {(1/4)5=
1/1024}
Congratulations, you’re a geneticist!!
Becoming Mendel
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Active Learning Activities
Figuring Probability Without a Punnett Square:
A Punnett square is not the only way to figure out the probabilities of the different possible offspring
of a mating. Multiplying the probabilities of each gamete can work too. (in word problems the word
“and” can represent multiplication, “or” usually indicates addition)
For example, in the mating AA x aa. The probability that the first parent will produce gametes with an
“A” is one. The probability that the second parent will produce gametes with an “a” is one. The
probability that the offspring will receive an “A” and an “a” can be found by multiplying the
probabilities- 1x1=1. Therefore, all (100%) of the offspring will be Aa. What is the probability that the
offspring will be AA? First A probability is 1, second “A” possibility is 0 (the second parent can’t pass on
an “A”). 1 x 0= 0; NO chance of offspring that are AA.
Let’s try a harder mating: Aa x Aa (do you remember the ratios of all the possibilities from a Punnet
square?)
•
•
Probability of offspring with AA- ½ chance of A from parent 1, ½ chance of A from parent 2. ½
*½=¼
Probability of offspring with aa- ½ chance of a from parent 1, ½ chance of a from parent 2. ½ *
½ = ¼Probability of offspring with Aa- ½ chance of A from parent 1, ½ chance of a from parent
2 OR (plus) ½ chance of a from parent 1, ½ chance of A from parent 2. Answer: ( ½ * ½) + ( ½
* ½)= ¼ + ¼ = 2/4 or ½
Here’s a couple of trihybrid crosses, see if you can follow along (to avoid some HUGE Punnett squares):
•
•
Mating AaBBee x AabbEE. What is the probability of offspring that are AaBbEe?
o Answer: ½ * 1 * 1= ½
Mating DdGgHh x DdGgHH.
o What is the probability of offspring that are DdGgHH? Ans: ½ * ½* ½ = 1/8
o What is the probability of offspring that are DDGGhh? Ans: ¼ * ¼ * 0= 0 (zero chance,
hh isn’t possible!)
Becoming Mendel
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Active Learning Activities
Section 9.2 Making Sex Cells
Directions for the
Student:
This lesson is designed for you to complete, on your own or in your study group.
Use your notes and follow along in the text, as you find necessary.
1. Explain the field of cytogenetics and the usefulness of a karyotype.
2. Distinguish between chromosomes, chromatids, ploidy, and trisomy.
3. Describe and draw the steps of Meiosis.
4. Explain the importance of tetrads and crossing over in Prophase I.
5. Name and describe some of the mistakes that can happen during meiosis, and
their outcomes.
Materials needed: colored pencils, markers, or crayons
We know now that Mendel’s “particles” are genes on chromosomes. Offspring must receive the right
balance of genes and chromosomes to be successful. The number of genes and chromosomes that
determine success is different for each species.
1. What is the name for the study of the chromosomes in
cells?
cytogenetics
In order to study the chromosomes, a cell
sample is needed. This can come from any part
of the organism, but for humans the most
common sample is taken from blood. The live
cells are grown for a few days in tissue culture
in media that encourages cell division, then
processed in test tubes to get the cells ready to
be viewed under a microscope.
The cells are in a solution and drops of that
solution are “splatted” onto microscope slides
(sometimes from 3 feet above!). The cells need
to burst open when they hit the slide, to allow
their contents to spill out and wash away,
leaving the condensed chromosomes to spill out
of the nucleus and stick to the glass slide.
2. Would you use a hypotonic or
hypertonic solution to cause the
cells to burst, and why?
hypotonic solution, the water will be drawn into the cells
because the concentration of solutes is higher inside the cell
3. Why do the live cells need to be
grown in culture for a few days?
Only actively dividing cells are useful, because the
chromosomes need to be condensed. So we are trying to get
as many cells as possible into mitosis.
Making Sex Cells
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Genetics and Meiosis
Active Learning Activities
One of the tricks of the trade is the chemical colchicine- it stops cell division by blocking spindle fiber
movement. It is added to the cell culture a few hours before the cells are put into test tubes. Thus a
picture of chromosomes spread out in a photo, as seen above, is often called a “metaphase spread.”
4. Answer the following questions about chromosomes and the interruption of cell division.
What are spindle fibers made of and
where do they come from?
they are made of microtubules and originate from the
centrioles
Are chromosomes always visible in the
cell? Are there parts of the cell cycle
when they are more visible?
In Interphase the chromosomes are not condensed, so they
are not visible in a light microscope. They are most
condensed and visible in cell division.
In the picture above, what are the two
round objects that are near to the
chromosomes?
they are nuclei from cells that did not burst, and since
chromosomes are not visible they probably were in
Interphase when the cells were harvested
After the cells have been burst onto the slide, the slide is dipped in specific stains to make the
chromosomes visible. Once they are dry, the scientist will scan each slide under a microscope for cells
that have spread out.
5. Why is it important for the
chromosomes to spread out?
each chromosome needs to be able to be seen separately
Burst cells that have left behind chromosomes that are well-spread out are photographed. Modern
photographic methods that rely on computers to distinguish each chromosome have thankfully replaced
the old-fashioned methods of printing the photograph and cutting out each chromosome by hand.
Actual Human Chromosomes
Graphic Depiction of Human Chromosomes
Making Sex Cells
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Active Learning Activities
The chart of chromosomes is closely examined for any irregularities from what is considered “normal.” A
standard was set for the numbering system- it is based on the sizes and centromere locations of the
chromosomes. The chart on the left is a picture of actual chromosomes; the one on the right is a cartoon
depiction (drawing) of the typical human chromosome banding pattern.
6. What is the term for a chart of chromosomes karyotype
that have been paired and arranged by size?
7. Is the chart showing actual chromosomes
from a male or female?
male- XY
Chromosome 7 is a medium-sized submetacentric chromosome. The banding pattern on this ideogram
has been drawn in detail, and the band that is highlighted in red is showing the location of the gene for
cystic fibrosis. The bands do NOT represent genes; there are over 2500 genes on chromosome 7.
8. Look carefully at the ideogram of Chromosome 7 and answer the following questions.
What does submetacentric
mean?
sub-under; meta-middle; centric- the
centromere. just off center
The letters p and q are used
to designate the two arms or
sides of the centromere. Is
“p” labeling the shorter or
longer arm of the
chromosome?
p designated the shorter arm, which is
traditionally positioned on top- even if the
centromere is considered in the center
Examine the numbering
system and explain the order
that the numbers are in.
the closer to the centromere, the lower the
number. Regions are subdivided by the
second number and the decimal, lower
numbers closer to the centromere
Compare two genes from a
Gene B in band 24.1 is closer to the
different chromosome, #1centromere, the number is lower
Gene “A” is in band q42.1 and
Gene “B” is in band q24.1.
Which of these genes is closer
to the centromere? How do
you know?
Making Sex Cells
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Active Learning Activities
9. Identify these terms associated with chromosome structure and numbers.
Explain the suffix “-ploidy” in your own words
a full set of chromosomes
What type of ploidy are humans (and almost all
animals)?
diploid (2n)
What word describes the relationship of the two homologous
chromosomes that are paired together?
In a human karyotype there are 22 pairs of
chromosomes that do not determine sex- what
term describes these chromosomes?
autosomes
In contrast to animals, plants are often polyploid, having odd or even large numbers of sets of
chromosomes. Some very familiar food crops are 6x, for example bread wheat, sweet potatoes, oats and
plums. Coffee, tobacco, durum wheat, pima and upland cotton are all 4x. There are over 300 varieties of
banana in the world, and they can be 2x, 3x, or 4x; the type of “sweet seedless” banana found in
supermarkets, known as the Cavendish, is 3x. Watermelon can also be 2x, 3x or 4x. The seedless variety
is 3x. A set of chromosomes for watermelon is 11 chromosomes.
Explore ploidy further by answering these questions.
10. How many chromosomes would you find in
a cell of a seedless watermelon?
33 To create seedless watermelon, a tetraploid is
crossed with a diploid (gametes diploid and haploid)
11. There are 14 chromosomes in a garden pea
plant, Pisum sativum. Explain in some detail
how a pea plant gets its 14 chromosomes
(think of Mendel’s experiments!)
Pollen from one plant’s anthers (gamete cells) that
contain 7 chromosomes; the stigma (ovary) of the
other plant has gametes of 7 chromosomes. At
fertilization they combine to created offspring with
14.
Making sex cells is about a type of cell division that will create gametes with the correct number of
chromosomes. Gametes come from precursor cells, in other words mother cells. Those mother cells are
diploid (in animals) and can divide in two different ways.
Before cell division, though, remember that all dividing cells spend a lot of time in Interphase. During
Interphase, the cell is performing its normal functions; but there are also activities that happen to
prepare the cell to divide. It is important that you remember and review what happens to the
chromosomes during Interphase, and some of the terminology used to describe chromosomes.
Making Sex Cells
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Active Learning Activities
12. Answer these questions about single- and double-stranded chromosomes.
Which of these two
chromosomes would be found
in the G1 phase of Interphase?
How do you know?
The green one- it has not gone through
replication yet so there is only one
strand of chromatin
What is the name of the process DNA replication occurs in S phase
that copies DNA so that
chromosomes become doublestranded? When does it
happen?
What term describes the
relationship of the two arms of
the red chromosome?
sister chromatids
An organism, like you, needs to perform mitosis to grow as well as repair damage. Mitosis is just one
type of cell division.
13. Answer these questions about types of cell division.
What are the four stages of mitosis?
prophase, metaphase, anaphase, telophase
In humans, how many chromosomes are in a mother
cell before it goes through mitosis? Are they singlestranded or double-stranded at the start of mitosis?
46 double-stranded chromosomes
How many daughter cells are produced by mitosis?
2 cells
In humans, how many chromosomes are in a daughter 46 single-stranded chromosomes
cell after mitosis? Are they single-stranded or doublestranded?
Another type of cell division is known as binary fission. prokaryotic cells, Bacteria and Archaea
What type of cells divide by binary fission?
What is the name of the type of cell division that
creates sex cells?
Meiosis
Where are gametes produced in humans?
eggs in ovaries; and sperm in testes
Making Sex Cells
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Genetics and Meiosis
Active Learning Activities
Cell division to produce gametes is unique, and happens in two phases. To simplify drawing meiosis, let’s
work with a cell that has a diploid number of 8, like the picture here.
14. First answer a few general questions about this cell.
The chromosomes are shown
condensed so you can see them, but
in Interphase they would not be
visible. Is this cell in G1, S, or G2
phase?
G2- the chromosomes are
double stranded
If this cell divides to create sperm,
what is that process called?
spermatogenesis
If this cell divides to create eggs,
what is that process called?
oogenesis
Recall that many things happen in Prophase to get a cell ready to divide. All the steps that happen in
Prophase of mitosis happen in meiosis, but in Prophase I of meiosis, the pairing of the chromosomes is
distinct.
15. Draw our 8-chromosome cell as it would look in Prophase I of Meiosis.
answer- note nuclear membrane breaking down, and chromosomes in tetrads
Besides creating cells with half the number of chromosomes, an important part of meiosis is allowing for
alleles on chromosomes to get mixed up. Prophase I is a very important phase of meiosis- so important
that it is estimated that it occupies 90% of the time that is takes to do meiosis. In Prophase I, the cell is
set up to go through meiosis correctly, condensing the chromosomes pairing up the homologous
chromosomes. In addition, Prophase I is the stage when alleles on chromosomes can change location.
This creates new combinations, which creates variety in the offspring of a species. For example, take a
woman who is heterozygous, or “Aa” for a gene. Say chromosome she got from her mom has the “A;”
from dad, “a.” When her eggs are developing, the “A” and “a” can switch places during Prophase I!
Making Sex Cells
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Genetics and Meiosis
Active Learning Activities
16. Answer these questions about Prophase in Meiosis I.
What is the term for the structure that is formed by
homologous pairs joining together in prophase I?
a tetrad
What events allow the alleles to change locations?
crossing over, or an exchange of chromatid
arms (the cross point is a chiasma)
This photograph is a metaphase spread of a cell that
had its chromatids stained dark or light before
Prophase I. What are the arrows pointing out?
homologous recombination
Dark and light sections on certain chromatids,
which demonstrates that crossing over took
place
Genetic recombination is really important to the overall health of a species because it creates new
combinations of alleles. We will focus in on two of the chromosomes from our 8-chromosome cell. At
each gene location, or locus, the two alleles are shown, one from each chromosome. The colors are
showing the size and boundaries of each gene.
17. Examine these chromosomes and answer these questions.
For which gene(s) is the cell
homozygous dominant?
I
For which gene(s) is the cell recessive? none
For which gene(s) is the cell
heterozygous?
G, H, J, W, X, Y, Z
Draw a single crossover to create a
chromosome that is FghIJ
this can be between the h and
I or between the I and J
What is the allele combination of the FGHIj
OTHER chromosome that is created by
your single crossover?
Now draw a double crossover in the
other chromosome to create wXYz
one line between w and x, the
other between y and z
What is the allele combination of the WxyZ
OTHER chromosome that is created by
your double crossover?
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Genetics and Meiosis
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Did you notice, in your double crossover, you created two chromatids that were the same as the
original? Basically, double crossovers cancel each other out.
18. What terms describe chromosomes after a crossover event?
What term describes a chromosome that has the
same alleles as the parents?
parental
What term describes a chromosome that has a
different allele than the parents?
recombinant
Prophase I deserves a lot of attention because of the important events that take place in that stage.
Continue now through all the stages of meiosis.
At the end of Meiosis I, our 8-chromosome cell will split into two cells that look like this:
What did the cell look like in Metaphase I and Anaphase I before it split into 2 daughter cells?
19. Draw them, and be sure to include all chromosomes and spindle fibers.
METAPHASE I
ANAPHASE I
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Genetics and Meiosis
Active Learning Activities
20. Summarize Meiosis I by answering these questions.
In the first division, Meiosis I, what is pulled apart- homologous chromosomes
chromatids or chromosomes?
Meiosis I is sometimes called the ‘reduction
they are haploid
division.’ At the end of Meiosis I what is the ploidy
of each daughter cell?
At the end of Meiosis I, how many chromosomes
does each daughter cell have? Chromatids?
4 chromosomes, 8 chromatids
At the end of Meiosis II, the 2 daughter cells will become 4 cells that look like this:
21. Draw one of the daughter cells from Meiosis I as it would look in Metaphase II and Anaphase II.
METAPHASE II
ANAPHASE II
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Genetics and Meiosis
Active Learning Activities
22. Summarize Meiosis I by answering these questions.
In the second division, Meiosis II, what is pulled apart- chromatids
chromatids or chromosomes?
At the end of Meiosis II what is the ploidy of each
daughter cell?
they are haploid
At the end of Meiosis II, how many chromosomes does 4 chromosomes, single stranded
each daughter cell have? Are they single-stranded or
double-stranded?
Unfortunately, meiosis doesn’t always work perfectly. One of the problems that can happen during
Meiosis is that the chromosomes, while they are in a tetrad, will not let go of each other and will get
broken unevenly. If this happens, the chromosomes can end up with missing pieces or pieces that get
stuck onto the wrong chromosome. These are known as translocations- a piece of a chromosome has
incorrectly changed locations. They are often visible in the banding pattern in a karyotype.
In a form of leukemia known as
CML, chromosomes 14 and 22
break and reattach to each other.
This puts two genes, BCR and ABL,
next together on the fused
chromosome which is sometimes
called the “Philadelphia
chromosome,” because it was first
described in patients in that city.
The BCR-ABL genes together make
a fusion protein that causes
cancer (CML).
This depiction of banded
chromosomes shows a
translocation where chromosome
14 has an extra chromosome 21
attached. The extra piece of DNA
was identified because its banding
pattern matched that of
chromosome 21. This patient
(whether a boy or girl) would have
Down syndrome.
Making Sex Cells
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Genetics and Meiosis
Active Learning Activities
Besides translocations, it is possible that, during either phase of Meiosis, the chromosomes do not get
pulled apart correctly.
23. Define these terms related to mistakes in meiosis.
What term describes a mistake during
meiosis that causes two chromosomes to be
pulled apart incorrectly?
nondisjunction
What is the term for a karyotype that shows
one extra or one missing chromosome?
aneuploid
What does the term trisomy mean?
three copies of an individual chromosome
Researchers believe that the frequency of mistakes in meiosis is significant, and many miscarriages early
in pregnancy are due to the embryo having the wrong number of chromosomes. Most trisomies,
therefore, are fatal. But there are a few that can survive at least to birth.
24. Answer these questions about trisomy
What trisomy causes the disorder known as Down Trisomy 21
syndrome?
Down syndrome is one of the only trisomies to
chromosome 21 is very small, contains less
survive to birth. Hypothesize why Down syndrome “critical” genes that can be in triplicate without
is a less severe disorder than other trisomies,
causing much harm.
including trisomy 13 or 18.
Explain why the patient in the banded karyotype
shown above, with a 14:21 translocation, would
have Down syndrome.
The patient has 2 normal #21s plus the
translocated section, so they have 3 copies of #21.
This is known as translocation Down syndrome.
Why do you think the frequency of infants born
with Down syndrome increases as parents get
older (especially over 40)?
The frequency of mistakes in Meiosis increases,
perhaps because the machinery of meiosis is older
and enzymes or microtubules don’t work as well.
Making Sex Cells
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Genetics and Meiosis
Active Learning Activities
Aneuploidy in the sex chromosomes is not fatal, but does cause some symptoms in certain cases.
Patients with only one X (XO) are females but have short stature, can have heart defects, and are
infertile. This is also known as Turner syndrome. The disorder known as Klinefelter syndrome is caused
by a person inheriting XXY. Their outer features are male at birth, but when they hit puberty they
develop breasts, wide hips, and very little facial hair. Some people with Klinefelter syndrome go
undiagnosed.
There is a sort of shorthand to summarize findings from a karyotype. A normal male would be
designated 46, XY. He has 46 chromosomes, and is male. A trisomy 13 female would be 47, XX, +13.
25. Write the notation for these types of karyotypes
How would you designate a male Down syndrome karyotype?
47, XY, +21
How would you designate a Klinefelter syndrome karyotype?
47, XXY
How would you designate a Turner syndrome karyotype?
45, X
Making Sex Cells
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Genetics and Meiosis
Active Learning Activities
Section 9.3 Outgrowing Mendel
Directions for
the Student:
Objectives:
This lesson is designed for you to complete, on your own or in your study group. Use
your notes and follow along in the text, as you find necessary.
1. Review the patterns of inheritance that differ from Mendel’s dominant/recessive
traits.
2. Practice Punnett squares with different patterns of inheritance.
3. Compare and contrast the different patterns of inheritance.
Simple dominant/recessive traits are a starting point to understand basic concepts, but in this section
you will learn about some of the nuances of inheritance.
1. Recall the simple dominant/recessive inheritance trait pattern Mendel studied:
How many phenotypes are seen in the F1 generation in a 1 phenotype
trait that has simple dominant/recessive inheritance?
What phenotype is seen in heterozygotes in a
dominant/recessive trait?
the dominant phenotype
How many phenotypes are seen in the F2 generation in a 2
trait that has simple dominant/recessive inheritance?
In a carnation or tulip, the pattern of inheritance is different. In the cross Red x White, the F1 are all
PINK. Crossing pink x pink gives F2 that are Red, Pink, and White.
2. What type of inheritance produces an intermediate,
or blending of the two phenotypes?
incomplete dominance
Dogs show many color patterns, but the pattern called “merle” is caused by a gene that causes a dilution
of color that gives the dog a mottled appearance. Border collies are one breed that exhibits this trait.
standard black and white
color
merle color, heterozygote, sometimes
have eyes of different colors
double merle homozygote,
dog often is blind and deaf
Outgrowing Mendel
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Genetics and Meiosis
Active Learning Activities
Because the merle phenotype is intermediate between the strongest and weakest color, it is considered
an example of incomplete dominance. Merle dogs are very popular with people seeking a border collie
puppy. A responsible breeder will try to avoid creating the double merle dog, which is mostly white,
because they often have major health issues including blindness and deafness
3. Use the letter ‘M’ to represent standard (darkest) color and ‘m’ to represent the most diluted color
(mostly white).
What phenotypes do you need to cross to produce dark x white MM x mm
a litter of all merle pups? What is the genotype of F1 are all Mm
the F1?
What type of coloration and in what ratio would
Mm x Mm
you get in pups from parents that are both merle? ¼ standard; ½ merle; ¼ double merle
What type of coloration and in what ratio would
you get in pups from a cross between a parents
that is merle and a parent that is standard (dark)?
Mm x MM
½ standard; ½ merle
Now let’s consider a different scenario for flower colors. Some flowers,
such as a petunia, have a different pattern of color inheritance that
neither simple dominant/recessive nor incomplete dominance:
Solid Red flowers x solid white flowers (P) produces F1 that are red and
white, with blotches of each. F1 x F1 (red/white together) produce F2
that are Red, White, and red/white together. Since both alleles are
contributing equally, this type of inheritance is known as co-dominant.
Both traits are in their original form, and visible.
4. For the petunias, that have red/white mixed together in the F1, answer these questions.
If 100 F2 petunias grow, how many of them would
you expect to be red/white (heterozygotes)?
50
If you mated a F1 red/white petunia plant with a
white petunia plant, what phenotypes would you
see in the F2?
This is Rr x rr. The F2 would be Rr or rr, so
red/white or white (no solid red)
A gardener wants to produce only white petunias. This is RR x Rr, only solid red and red/white can be
If he crosses a solid red petunia with a red/white produced.
petunia, can he get white flowers? Why or why
not?
In humans there are several examples of co-dominance. Many diseases, like Tay Sachs disease, are
caused by enzyme deficiencies. Homozygous recessive individuals have two copies of the deficient gene,
therefore no working enzyme, and develop the disease. In heterozygotes, there is a copy of the normal
Outgrowing Mendel
26
Genetics and Meiosis
Active Learning Activities
allele, and a copy of the defective allele. A simple blood test shows that both versions of the enzyme are
expressed in a heterozygote, event though the defective enzyme is not helping the individual at all. It
seems that having half the amount of functioning enzyme is enough to keep you from developing the
disease!
Some genes have more than two alleles. Human A, B, AB, and O blood types are an example- the alleles
are designated as a superscript (IA, IB, and i). In rabbits, coat color saturation shows at least three
phenotypes. The full color phenotype is dominant (C), but there are 3 recessive alleles, cch, ch and c.
phenotype
genotypes
full color
CC, C_
chinchilla (diluted coloring)
cch, cch or cch, c
himalayan (black ears, nose & feet)
ch ch or chc
albino
cc
Scenario: A full color male rabbit whose mother was albino is mated to a chinchilla-colored female
whose father was albino.
5. Draw a Punnett square for the scenario and include labels.
full color male
chinchilla female
C
c
cch
C cch
c cch
c
Cc
cc
6. If the resulting litter has 8 rabbits in it, how many of each of the following would be expected?
full color
4 rabbits (50%)
chinchilla-colored
2 rabbits (25%)
himalayan
0 – the allele is not in either parent
albino
2 rabbits (25%)
Multiple allele inheritance is due to there being several alleles, or version of a gene. Some traits show so
much variety across a species that the pattern of inheritance is very hard to determine. In many cases
the trait can be quantified, from least prominent to most prominent, and everything in between.
Outgrowing Mendel
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Genetics and Meiosis
Active Learning Activities
7. Answer these questions with respect to a trait that can be represented by a bell curve:
What type of distribution is seen in a bell curve?
continuous distribution
What type of inheritance pattern is this called?
multiple genes, or polygenic
Name three human traits that follow this pattern
weight, height, skin color
What is the name for the type of inheritance that
also is affected by the environment, such as a
person’s diet or sun exposure?
multifactorial
8. Explore this type of inheritance a little more in depth with these questions:
Assume that human height is determined by
3 genes. If two individuals are tall (defined
as 4 or more dominant alleles) could they
have a very short child (defined as 4 or more
recessive alleles)? Write out the genotypes
of the parents and children to support your
answer.
Answers can vary but all should indicate YES, they could
have a short child.
Identical twins live in opposite sides of the
world- one on a Caribbean island and the
other in Sweden. Since they have identical
genetics, will their skin tones be the same?
Why or why not?
Their skin tone will be different due to environmental
factors, namely exposure to UV rays.
Example phenotypes: AaBbCC and AaBbCC could
produce a child that is aabbCC
If they moved to be together in the same environment,
their skin tone would be closer to the same
Compare and contrast polygenic inheritance Both types of inheritance produce a variety of
and multiple allele inheritance.
phenotypes, 3 or more depending on how many alleles
there are. However, in multiple alleles all of the
variation is due to one gene that has many alleles, or
different versions (technically different sequences). In
polygenic traits, several genes produce proteins that
effect that trait, so that a gradient of phenotypes can
be observed.
So far we have been focusing on genes that do not discriminate between whether they come from the
mother or the father. These genes are known as autosomal, because they are found on chromosomes
that are in every individual regardless of sex. But in many animal species, the sex of an individual is
determined by the inheritance of different chromosomes. There can be hundreds of genes on sex
chromosomes, so the inheritance pattern of these genes differs based on whether the offspring are
male or female, and which sex chromosome they get from the father or mother.
Outgrowing Mendel
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Genetics and Meiosis
Active Learning Activities
9. Answer these questions about genetic inheritance of sex in humans:
What chromosomes are inherited in humans to
produce a male? A female?
XY- male
What are some genes that are found on the X
chromosome?
red-green color blindness, hemophilia, Duchenne
muscular dystrophy
How is a trait that is sex-linked represented, so
that the gene can be tracked on a sex
chromosome?
superscript on the X,
XX- female
XA or Xa
Scenario: A woman whose father was colorblind marries a man that is colorblind. Red/green
colorblindness is a recessive sex-linked trait.
10. Draw a Punnett square to represent this mating (choose a letter to represent the colorblind gene).
father
mother
Xb
Y
XB
X B Xb
XBY
Xb
X b Xb
XbY
11. Answer these questions based on the scenario:
Can the couple have a colorblind son? A colorblind yes to both
daughter?
If a son is born with normal vision, from whom did his mother
he get the “normal” allele?
If a daughter is born with normal vision, could she she only can be a heterozygote (carrier) because
be a homozygote? A heterozygote? Why or why
she has to get the recessive allele from her dad
not?
Many of the genetic traits on the X-chromosome can be called sex-linked, but it is more accurate to call
them X-linked. The Y chromosome also carries genes, known as holandric genes, but many less than the
X chromosome. One notable gene on the Y chromosome is responsible for producing male genitals.
Other genes contribute to secondary sex characteristics and affect spermatogenesis. No truly Y-linked
disorders have been identified in humans.
Outgrowing Mendel
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Genetics and Meiosis
Active Learning Activities
Watch Out For Lethal genes
Achondroplasia, or dwarfism, is a trait that is a dominant condition. It usually shows up as a
spontaneous mutation, where parents that are average height have a dwarf child due to a change in the
sequence of the gene in one of the parent’s gametes. Persons who are average height are homozygous
recessive, a person with achondroplasia is a heterozygote. Homozygous dominant infants are stillborn or
die shortly after birth. This is known as a lethal disorder; one of the possible genotypes is not viable and
this changes the probabilities when interpreting a Punnett square.
12. Use the letter “D” to represent the gene for achondroplasia, and autosomal dominant trait. Fill in
the genotypes below
Phenotype
average height
Genotype
achondroplasia
dd
Dd
stillborn homozygote
DD
13. Now, draw a Punnett square for a mating between 2 dwarf adults.
Parent 1 Gametes
Parent 2
Gametes
D
d
D
DD
Dd
d
Dd
dd
14. Given the Punnett square you just made, answer these questions for a mating between two adults
with achondroplasia. Note-one of the possibilities is lethal, so there are 3 possible outcomes
instead of 4.
Which square of your Punnett square can
the DD square
you cross out, or eliminate from calculations,
since the fetus will not be viable?
What are the chances that these parents will 2 out of 3 or 66%
raise a child that is dwarf like them?
What are the chances that these parents will 1 out of 3 or 33%
raise a child that is of average height?
If they can have a child that is average
height, can that child pass the dwarf trait on
to his children? Why or why not?
no chance of passing on the trait, the average-height
child is dd therefore does not carry the gene for
achondroplasia (unless of course he/she also has a
spontaneous mutation!)
Outgrowing Mendel
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Genetics and Meiosis
Active Learning Activities
Section 9.4 Growing Outside the Box
Directions for
the Student:
Objectives:
This lesson is designed for you to complete, on your own or in your study group. Use
your notes and follow along in the text, as you find necessary.
1. Define linkage and homologous recombination
2. Draw chromosome maps based on recombination frequencies
3. Explain transposons and their possible roles in disease and forensics
4. Discuss the findings and significance of the Human Genome Project
Mendel’s Law of Independent Assortment explains how two traits on different chromosomes can be
combined in different ways. Diploid organisms, like humans, have pairs of chromosomes. We know that,
during cell division, assortment of traits happens because chromosomes get pulled apart.
1. Answer these questions to refresh what you have learned about chromosomes and meiosis.
What term describes the relationship between the two
chromosomes in a pair?
homologous
What is the term for a pair of double-stranded chromosomes tetrad
that are joined together during prophase of meiosis I?
How and when can allele combinations be shuffled during
meiosis?
You may immediately recognize
these figures as chromosomes.
Each colored area represents a
gene. As we are learning in
genetics, an individual can be
homozygous recessive,
homozygous dominant, or
heterozygous for each gene.
Suppose this individual has the
following genetic makeup:
•
Homozygous recessive for
genes C and P
•
Homozygous dominant for
genes B, E
•
Heterozygous for genes
A,D,Q,R, and S
prophase of meiosis I, when they are in
a tetrad there can be cross-over events,
known as homologous recombination
A
a
B
B
c
c
D
E
p
p
Q
q
R
r
S
s
d
E
2. Write in the missing allele in
each box that is provided.
Growing Outside the Box
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Genetics and Meiosis
Active Learning Activities
The two chromosomes show a group of alleles that are together on a chromosome. The larger
chromosome has the alleles ABcDE and the smaller chromosome has the alleles pQRS. (you filled in the
homologous chromosomes’ alleles). Notice that genes can be different lengths, depending on the RNA
that they code for.
3. Look closely at the chromosomes and answer these questions.
Do these drawings represent chromosomes in a
cell before or after S phase? How do you know?
before; each is single stranded
What is the darkly-shaded area on each
chromosome?
the centromere
Will genes A and Q assort independently? Why or yes, they are on different chromosomes
why not?
Will genes D and E assort independently? Why or
why not?
no, they are closely linked
Genetic linkage is a mathematical concept, related to how often two alleles will stay together in the
offspring. In your genetic studies you have learned many ratios for expected outcomes of genetic
crosses. For example, in a monohybrid cross for a simple dominant/recessive trait, where the F1 are
heterozygotes, the F2 will have a phenotype ratio of 3:1 (dominant:recessive).
4. Answer the questions related to ratios in dihybrid crosses of two simple dominant/recessive traits.
What ratio of phenotypes is expected in the F2 if the two
genes are on different chromosomes?
9:3:3:1
What ratio of phenotypes is expected in the F2 if the two
genes are very tightly linked (no recombination at all)?
3:1
What ratio of phenotypes did Bateson and Punnett
observe when the two pea plant genes that they crossed
were flower color and seed shape?
11:1:1:3, note that the order does matter!
Can two genes that are on the same chromosome assort
independently? Support your answer.
Yes, if they are very far apart, because the
chance of a double cross-over in between
them is very high.
Genetic maps are a representation of relationships between genes on a chromosome, based on the
frequency of phenotypes that are due to recombination. In our chromosome drawings, the larger
chromosome has the alleles ABcDE and the smaller chromosome has the alleles pQRS. These are the
Growing Outside the Box
32
Genetics and Meiosis
Active Learning Activities
parental chromosomes; if there is no crossing over the offspring will inherit the same group of alleles.
But if crossing over occurs, the alleles can switch places.
5. Answer these questions about crossing over in the drawn chromosomes
If a single crossover occurs in the area from the p gene to the q gene, what pqrs and pQRS
will the new allele combinations be on the two recombinant chromosomes?
If a single crossover occurs in the area from the C gene to the D gene, what ABcdE and aBcDE
will the new allele combinations be on the two recombinant chromosomes?
Assume that a double crossover happens. Where would the two crossovers among/between the A and
need to occur to create two chromosomes with the alleles ABcDE and
B genes and the C and D
aBcDE?
genes
Rank these gene pairs according to how often they can be recombined
A/B
(assume the length of each gene is to scale). 1= most likely to recombine; 5=
B/D
least likely to recombine.
5
B/E
2
A/E
1
D/E
4
3
Challenge question: A pair of parental chromosomes in a mouse have the alleles FGhiJ and fgHij. The
recombinant chromosome found in an offspring of this mouse has the alleles FGhij. Where did the
crossover take place on the parental chromosome to create the new recombinant chromosome?
between the H and I or between the I and J (more likely between the farther apart genes, but we don’t
have that information).
The frequency of recombination can give us an estimate of the relative position and distance of a set of
linked genes.
6. Draw a chromosome map (gene order and distances) of these 4 genes based on this data:
Gene
combination
Frequency of
recombination
L>O
10
N>O
2
M>N
21
L>M
13
Chromosome map
Growing Outside the Box
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Genetics and Meiosis
Active Learning Activities
Everything you have worked on in this section, so far, has involved genes that have a permanent place
on a chromosome. Surprisingly, though, not all genes stay in their place.
7. Genes that do not stay in place are called “jumping genes,” answer the following questions about
them.
What is the technical term for genes that can
“jump” from one location to another?
transposon
What is unique about the structure of a
“jumping gene?”
they have a short sequence on each end that allows
them to loop out of the DNA and they can force
themselves to be inserted into a different region
In human cells, a 300 base pair-long section of DNA, known as an Alu sequence, is repeated
approximately 1 million times. An Alu sequence does not code for a protein, so until recently it was
thought to be “junk” DNA. But an Alu sequence can move around the human genome, and goes through
an intermediate step of having the mRNA sequence for the Alu sequence copied back into a DNA
molecule.
8. What is the name for Alu sequences and
other transposons that can be converted
from RNA into DNA?
retrotransposon
Alu sequences give scientists an interesting tool to study how mutations and evolution occur. They also
are a marker in forensics to identify people, based on differences in their DNA. In some cases, an Alu
sequence can “jump” into the middle of a normal gene, causing a spontaneous mutation in a gamete.
This type of mutation is not just the change of a single nucleotide, but rather an interruption in the gene
that causes a big change in the protein. In some cases, DNA testing has shown that Alu insertions have
caused diseases such as neurofibromatosis, hemophilia, familial hypercholesterolemia, and diabetes
type II.
Since the 1990s, modern technologies have changed the way we study inheritance. Mendel and many
since him spent a lot of time tracking traits, alleles, and genes. This is definitely useful, but a “one gene
at a time” approach is not very useful when a human has over 20,000 genes.
9. Answer these questions related to modern genomics:
What project determined the complete
sequence of a human’s DNA and when was it
completed?
Human Genome Project completed in 2003
Growing Outside the Box
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Genetics and Meiosis
Active Learning Activities
What types of things can scientist learn from
comparing genomes such as human’s to a
chimpanzee’s?
what genes we have in common, evolutionary
changes, changes in gene linkages, etc.
Think back to the genes L, M, N and O that you
mapped based on their recombination
frequencies. How has the study of genomes
changed how we would determine how far
apart each gene is on a chromosome?
Assuming each gene could be located to an exact start
and stop point on the chromosome, then the exact
number of base pairs between each gene could be
determined
Since the human DNA sequence was published, genes that control “hidden” phenotypes, such as
whether you can digest lactose, or if you have fast or slow metabolism, have been discovered. A new
medical field, pharmacogenomics, has emerged. In pharmacogenomics, the medicine or treatment that
is best for a person is based on their DNA sequence. For example, until recently, a patient with
depression is prescribed a medication for them to “try” for a couple of months. If it doesn’t work, they
try a different one, and so on. As it turns out, some people have enzymes that will break down a
medication before it has a chance to work. Now, genetic tests can determine which antidepressant is
right for a person, based on the DNA sequence of a few key genes! Cancer and other diseases are now
treated more effectively using pharmacogenomics methods.
Keeping track of, and being able to search through, all the data generated by studying whole genomes is
an enormous undertaking.
10. If you wanted to have a major in college
that prepared you to work with the
massive amounts of data that Genomics
produces, what would it be?
BioInformatics (or Information Technology if a
university didn’t specifically have BioInformatics)
Clearly, the study of Genetics has come a long way since Gregor Mendel. There are many career paths
you can follow if you enjoy Genetics- agriculture and horticulture management, genomic study of
evolution, genetic studies to clarify classification and taxonomy relationships, forensics, tracking
diseases, developing new medicines and treatments, computer database management, genetic
counseling, and so on!
Growing Outside the Box
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