Download APPLYING THE

OHAPTER
33
APPLYING THE PRINCIPLES
OF GENETICS
33-1 Laboratory lnvestigation: Using Poker Chips
to Understand Hybrid Grosses
33-2 A Programmed lntroduction to Genetics
33-3 lntroduction to Solving Hybrid Cross Problems
33-4 A Review of Hybrid Cross Problems
33-5 Hybrid Gross Problem Set
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fuplying the Principles of Genetics
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Cfropter 33
gppfuin7 tfte gincipfes af Qenetiu
Wett dmu is fietter tfian weff soi[.
Ben
Franklin
33-1 Laboratory tnvestigation
Using Poker Ghips to
Understand Hybrid Crosses
Objective
By the end of this lab, you should be able to diagram a hybrid cross using the
appropriate symbols for gene formulas.
Manipulating the poker chips will help you understand how the genes are
distributed to offspring lrom the parents.
Work in groups of 2 at your table during that part of the lab when the poker chips
are required. Then work individually on the programmed part of the lab. You may be
given a quiz at the completion of the activity.
You will find two containers on your table, one marked male, the other marked
female. t I Each poker chip in the male container (14 colored, 14 white) represents a
sperm cell. Each poker chip in the female container (14 colored, 14 white) represents
.an egg cell.
I I
One person at the table should do
Thoroughly mix up the chips in each container.
pull
out
a chip from each container at
the following: Without looking in the containers,
the same time, and place them side-by-side on the table as a pair. Arrange the poker
chips in pairs as shown on the next page. Keep doing this until all of the poker chips
have been drawn from the containers.'
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Applying the Principles of Geneiics
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@@
@
etc.
1. What does each chip in the female container represent?
1. An egg
2. The placing together of a poker
chip from each container represents what process in
(Remember what each chip represents.)
living animals?
2.
fertilization
3. Each pair of chips represents which of the following? a. sperm
c. a zygote d. egg cells e. egg shells f. a winning bet '
3. c.
cells b. an embryo
a zygote (or a new individual) or a iertilized
egg.
1
4. Let C represent a colored chip and c represent a white chip. (You will see the reason
for this shortly) Each container had 14 C's and.14 c's.
What was your chance of drawing a C from eithei container? Express your answer
as a fraction.
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Applying the Principles ol
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4.
1tz
5. What was your chance
5.
6.
of drawing a c from either container?
1t2
What was your chance of drawing a G irom the male container and a C from the
female container at the same time?
6.
1i+ (Second law
of Probability'
12X1rz
=1r4\
is the chance of drawing a c from the male container and a c from the female
container at the same time?
7. What
' 7. 114 (tnxlrz= v+) This is the chance of ge,tting an
offspring with the gene formula cc.
)
L What is the chance of getting a C from the male container and a c from the female
container at the same time?
8. 1t4 (tzchance of getting cxtn=tn)
9. What
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is the chance of getting the pair Cc in any manner what-so-ever?
Applying the Principles ol Genetics
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9. 112eX112c=114Cc
1l2cX1l2C=1l4cC
114
Cc +
114
cC =
112
Cc
Create a chart like the one below and fill in the columns based upon the results you
obtained with the chips. Also place your data on the board for your table.
Possible pair
combinations
Use symbols
Number of
times each
combination
occurred at
your table
What frac-tion of total
pairs is this?
What percentage?
Percentage
expected but
probably not
obtained
Check to see if your calculations for "/" are correct. The following is
a review on
%
calculation:
Example: What percent is 8 out of a total of 30? This can be expressed as 8/30. To
obtain o/" lrom a fraction, divide the denominator into the numerator. Then
multiply by 100. ( I + 30 = .266, .266 X 100 = 26.6 %) Did you calculate all
percent values in the chart in similar manner?
10. Place your team's results in the class results chart on the chalk board.
t-l
After all
teams have placed their data on the chalk board, answer the next question. (While
waiting, you might need to go on reading and come back to this question.)
What is the average "/" lor each category for your class?
'10. The percentages will vary with each class.
Copy them from the board for #10.
'11. Which set of percentages, the class averages or your team's data, comes closest to
25"/" lor each category?
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Applying the Principles of Genetics
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11. The class average l" dala usually comes
closer lo 25h for each category. On rarer
occasions, the team data is closer.
12. Why is the class average data usually closer than the team data is to the expected
25Y" lor each category?
12. The greater the sample size, (number of cases)
the greater the accuracy of the data and the greater
the chance is for the data to come closer to the
expected results.
13. Review:
Each container of chips represented a parent. One is female and one is male.
Each parent has two kinds of genes.
PlCcXCc
Each parent can contribute one kind of gene or the other. NOT BOTH. What is the
This is illustrated by picking a poker
chance that the male will contribute a C?
chip out of the container marked male. What was the chance that the female could
Placing the two poker chips together as a pair on the table
contribute a C?
represents fertilization and the formation of a new individual with the gene
combination of CC (gene formula) The chance of obtaining this offspring is 1/4.
-
13. 1t2,
112
14. An alternate way to show what happens is to use a method called the
Punnett
placed
The
at
of
chart.
the
top
the
are
female
Square. The eggs possible from the
possible sperm cells are placed along the side of the chart. Next the eggs and
sperm.are combined in the 4 boxes to show the 4 different possible offspring and
the fractions of each according the Second Law of Probability. This is done as
follows:
\-t-,.Ch
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Applying the Principles of Genetics
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Parents (P 1
)
X
Cc (male)
Cc (female)
lf C represents a factor for colored fur in mice and c represents a factor for white fur, what
fraction of the offspring from parents Cc X Cc would you expect to have colored fur?
14.
114 CC + 1/2 Cc = 3/4 with colored fur. (C is
dominant over c)
15. What fraction of the offspring in cross Cc x Cc would you expect to have white fur?
15.
114
cc with white fur
16. lf we would expect offspring with gene pairs determined above
and 1/4 cc), then why did you not get 25"/" CC', 50% Cb and
CC, 1t2 Cc
25Y" cc with your
poker chips?
16. Your poker chip percentages were not quite
25V", sOV", 25Y" because the percentages are
only. Experimental results usually
come close but are not exactly those
EXPECTED
percentages. The actual experimental results
are affected by chance and will usually vary from
of
examples are used, the expected comes closer
to the actual results obtained:
the EXPECTED. When large numbers
Please return the poker chips to the appropriate
containers. Put 14 colored and 14 white in each
container.
1
t
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Applying the Principles of Genetics
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(1/4
17. lf you have understood the previous example for a genetic cross when poker chips
were used to visualize the distribution and recombination of genes, then you should
be able to solve the following sample test question:
ln certain dogs, dark color (D) is dominant to light color (d).
Ddx
What color is each of the parents in the above cross?
17.
18.
Both are dark in color.
Determine the gene formulas, appearances and the fractions of each for the
offspring using a Punnett Square.
18.
1/4DD + 1l2Dd +
3/4 dark + 1/4 light
ll4dd
19. This next sample question is a little different. One parent is light and the other
dark.
:tDdxdd
Determine the gene formulas, appearances of otfspring andthe fractions of each.
19.
Parents (P 1
)
Dd (male)
or llzDd + 1l2dd
(1/2dark+ 1/2 light)
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Applying the Principles ol Genetics
2A
X
dd (female)
is
20. ln the following crosses, C = colored fur and c = white fur. List allthe possible gene
formulas and appearances for offspring for the following crosses. What fraction of
each appearance is obtained?
Cross
CC Xcc
Cross
CcXcc
ccXcc
Cc XCc
Cross
Cross
Check the resuhs wilh the others at your table.
21. ln pea plants, tall plant genes are dominant to short plant genes. Cross a tall pea
plant (carrying a gene for shortness) with a short plant. What fraction of the
offspring will be tall and what fraction short?
Check the results with the others at your table.
33-2 A Programmed lntroduction to Genetics
Obiective
On a quiz that follows this program, you should be able to diagram a hybrid cross
using the appropriate symbols for gene formulas. Also be able to state definitions
for dominant, recessive, genotype, phenotype, homozygous and heterozygous.
Animals and plants possess a great variety of traits. Humans have various hair and eye
color, size, etc. Plants can be tall or short, have red, yellow or white flowers, etc. A
guinea pig can have white or brown fur which can be long, short or curly. All of these
TRAITS express how the individual looks or appears to you. GENETICS is the study of
how these hereditary traits are passed on from one generation to another. lt is a
fascinating study and one that will enable you to understand how you may have
inherited certain hereditary characteristics you possess. You will also understand how
traits you have would be passed on to your offspring and future generations.
When you have completed this program you will understand the meanings of basic
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Applying the Principles ol Genetics
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genetics terms and the ways in which plants, animals or people are symbolized to show
their genetic make-up.
Write your answers on a separate sheet of paper. Use the paper to cover the answers
as you progress through the program.
1. Write the definition for GENETICS presented earlier without looking back.
1. GENETICS is the study of how hereditary traits are
passed from one generation to the next.
2. List each of the traits mentioned in the first paragraph in this topic.
2.
Hair, eye color and size for humans; tall, short, red
flowers, yellow flowers, white flowers for plants; white or
brown fur, long, short or curly fur for guinea pigs.
3. List some specific genetic traits that you possess.
3.
.
Answers will vary (you might have listed specific hair
and eye color, straight or curly hair, size, complexion or
race, facial and body features.
4. BASIC CONCEPT NUMBER ONE:
EACH ONE TRAIT is determined by TWO GENES. The genes are on chromosomes
inside of the nucleus of each one of your cells. You will learn more about this later. lf
a person has blue eyes, how many genes would be needed to produce blue eyes?
4. Two
5. lf a geranium plant was a special short variety and produced only red flowers, how many
genes would that plant possess for those two traits?
5. Four (2tor height and2forflowercolor)
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6. A person has blond curly hair and blue eyes. How many genes would be needed to
produce these traits?
6. Six genes (2 lor hair color, 2 tor hair curliness and 2 for eye color)
7. ln order to figure out how traits are passed from generation to generation, it's
convenient to use symbols to represent traits. For example, tallness in plants is
represented with a T, red flowers with an R and brown eyes with a B. The gene for
shortness is represented by a t and not an S or s. The gene for white flowers is r and
blue eyes is b. Fill in the symbols for the traits below:
Height Flower Color
Tall
Red
Short White
7.
T
Eye Color
Brown
Blue
r
t
R
B
White
Brown
Blue b
Red
Short
that the first letter of the dominant gene is always
used and is made the capital letter. lf short is dominant
over tall, short would be symbolized as S and tall as s.
Tall
*Note
8. Since each trait is represented by 2 genes, a tall plant would be represented as TT
and a short plant as tt. The observed appearance of a trait is called its
PHENOTYPE. The symbolized form. or gene formula for that trait is called its
GENOTYPE. Write the genotype and phenotype for a tall plant.
8. TT
tall
or
Tt
tall
9. What is the genotype of a brown eyed person?
What is the phenotype of a short plant?
What is the genotype of a short plant?
9. A brown eyed
person could be BB or Bb
The phenotype of a short plant = short
The genotype of a short plant = tt
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10. When a tall pea plant is crossed with a short pea plant, all the offspring are always
tall. This means that tallness is DOMINANT over shortness. Shortness is said to
be a RECESSIVE trait. This is the reason geneticist use capital letters to represent
DOMINANT traits and lower case letters to represent RECESSIVE traits. Which is
the dominant flower color, red or white? Which eye color, blue or brown, is the
dominant trait? Which eye color is RECESSIVE?
10. Red,
Brown,
Blue
11. Are dominant traits symbolized with capital or lower case letters? Are recessive
traits symbolized by capital or lower case letters? The letter selected as the symbol
always comes from which trait - dominant or recessive?
11. Capital,
lower case,
dominant
...
TT x tt
all the offsprings are tall. Remembering that each parent contributes genetic
material to the offspring, what would you predict to be the genotype of these tall
12.11a tall plant is crossed with a short plant
offspring?
12. Tt
13. Note that this new plant has a gene for tallness and a gene for shortness. The fact
that the plant is tall illustrates the principle of dominance. The t gene for shortness
is dominated by the presence of the T gene for tallness and shortness is not
expressed. lf a brown eyed person BB is crossed with a blue eyed person bb, what
would the genotype of the offspring be? What would the phenotype be?
13.
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Bb,
brown
Applying the Principles ol Genetics
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14. Crosses are often diagrammed as follows:
X
Red flowered
pea plant
(male)
Both genes
dominant
White llowered
pea plant
(female)
t
Offspring
What are the genotypes for the 2 parent plants above?
RR
14.
(male), rr (female)
15. What would the genotype and phenotype of the ofispring from the above cross be?
15.
Rr,
red
16. Two terms are routinely used by geneticists to distinguish between the 2 ditferent
types of genotypes. Notice that a genotype can have the same genes in the pair:
TT, tt, or RR, rr. This kind of genotype is called a HOMOZYGOUS genotype.
Homo means "same" and zygous means "in the zygote", therefore HOMOZYGOUS
means the 2 genes in the zygote are the same. Also note that the 2 genes in the
This condition is called
zygote can be different, as with Tt, Rr, or
HETEROZYGOUS. Hetero means different. lndicate whether each of the
following genotypes are homozygous or heterozygous: FB, Hr, rr, Aa, YY, DD
Bb.
16. homozygous
heterozygous
homozygous
heterozygous
homozygous
homozygous
"Also note that a brown eyed person can be either BB or Bb
17. ln review, and without looking back, see if you can define the 6 terms presented in
HETEROZYGOUS
this program. GENOTYPE PHENOTYPE HOMOZYGOUS
DOMINANT RECESSIVE
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Applying the Principles of Genetics
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17. GENOTYPE - The gene formula of an individual
PHENOTYPE - The observed appearance of an individual
HOMOZYGOUS - When both genes of a genotype are the
same
HETEROZYGOUS - When lhe 2 genes of a genotype are
different
DOMINANT - The gene of the pair that dominates over the
other and its trait is expressed. (Symbolized with
capital letter)
RECESSIVE - The gene that does not express itself when
paired with a dominant gene. (Symbolized with
lower case letter)
R
EVI EW
18. See if you can apply these definitions to the following statements: When we notice a
person's blue eyes, we are noticing his (genotype or phenotype).
How is a blue eyed person symbolized?
When one symbolizes a trait, what it is called?
This genotype for blue eyes is (homozygous or heterozygous)?
The symbols show which eye color is dominant and which eye color is recessive.
18.
Phenotype,
bb,
genotype, homozYgous,
brown, blue
1g. See if you can assign symbols for genotypes according to the principles learned'
When an animal with curly hair is crossed with an animal with straight hair, all the
offspring are curly haired. The curly-haired parent would appropriately be
The
symboliied as _ and the straight-haired parent would be symbolized as
hair. Which
and would have
oifspring would be symbolized as
-. trait is
dominant?
-
19. CC, cc, Cc, curlY, curlY
20. On the quiz that follows, you should be able to apply these definitions to questions
on the quiz. Review to prepare for the quiz on this programmed topic.
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Applying the Principles of Genetics
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33-3 lntroduction to Solving Hybrid Cross Problems
Ob
jective
You will be expected to be able to solve hybrid cross genetics problems by
using the "Punnett Square."
Place all answers on your own paper. Cover the answers as you go.
1. Two parents have brown eyes and also
carry genes for blue eyes. Brown eyes (B)
are usually dominant over blue (b) eyes. What is the genotype of a person that is
homozygous for brown eyes? What is the genotype of a person who is homozygous
for blue eyes? What is the genotype of a person who is heterozygous for brown eyes
but carries a gene of blue eyes?
1. BB, bb,
Bb
2. Now examine a cross between two parents who are heterozygous for brown eyes.
The cross can be written as follows:
BbXBbPl
The P1 indicates the "1st parents." The "first offspring" are referred to as the F1
generation. The "second offspring" or grandchildren of the P1 are called the F2
generation.
eggs
To determine the F1 offspring, a box called the
Punnett Square can be used. lt's one of
the simplest ways to solve this type
b
of
B
problem.
square,
To determine the offspring square by
one simply moves the gene found above and the
one found to the left of the square into the box to
create pairs of genes.
sperm
b
When this is done for the left side, the sQuare will appear as follows:
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Applying the Principles of Genetics
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eggs
Copy this square onto your own
paper and fill in the right side of
the square using the same technique.
sperm
eggs
BI
2.
BB
Bb
Bb
bb
Now indicate what eye color each
of the four offspring will have.
sperm
b
2.
3.
BB =
112
What fraction of the
blue eyes?
4.
Ch
Bb
- Brown,
bb = blue
Remember that when sperm cells are formed, only one gene of the pair can go into a
sperm cell. According to the laws of chance that you demonstrated with coins, cards
and dice, What fraction of the sperm will carry the B gene? What fraction will carry
the b gene?
3.
4.
Brown,
33
Fl
B and 112 b
offspring would have brown eyes? What fraction would have
3/4 brown eyes and 1/4 blue
These are called the PhenotYPe
fractions or ratios.
Applying the Principles o{ Genetics
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5. What are the fractions lor each genotype?
5. 114 BB, 1l2Bb, l14bb
(These are called the genotypic ratios)
6. Determine the offspring for the following cross using the Punnett Square method:
BbXbbPl
6.bb
'l "_1" | "
ol un
lon
I
7. What are the phenotypic and genotypic ratios for the F1 offspring?
.
7. Phenotypic ratios = 112 brown + 1/2 blue eyed
Genotypic ratios =112 Bb + 1l2bb
8. Apply what you have learned to this next problem. ln pea plants, tall plants (T) are
dominant over short plants {t). Cross the following to determine the F1 offspring:
(Give the phenotypes, genotypes & lractions of each.)
fixttP1
8.
all
Tt
(100% tall)
9. Now cross the F1 with itself. (Tt X Tt ) This is called an F1 cross. (Give the
phenotypes, genotypes & fractions of each for the F2.)
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9.314 tall + 1/4 short
114Tl + 112 Tt + 1/4
tt
10. lf 40 seeds were planted from the above cross, how many tall plants would grow?
How many short plants?
10. 30 tall and 10 short Plants
11. ln pea plants, round seeds are dominant over wrinkled seeds. Cross a
heterozygous round seeded plant with wrinkled seeded plant. Assign the symbols
and determine the genotype and phenotypes of the F1 offspring.
11. The cross would be: Br X rr
The F1 offspring would be 112
round (Rr) and 1/2 wrinkled (rr)
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33-4
A Review of Hybrid Cross Problems
Objectlve
You will be expected to apply the principles of solving hybrid crosses to the
problems that follow.
Work out the following problems on your own paper. Show all your work for each
problem. Circle the final answer or answers. No late papers will be accepted after the
answers have been given in class...
1. Usually, but not always, human
eye color is inherited as if brown eyes were dominant
and blue eyes were recessive. Assume that this is correct for this problem and any
others in this unit. (B= brown, b=blue)
A blue-eyed mother bb is married to a brown-eyed man (heterozygous Bb). What is
the chance that their lirst child will be blue-eyed? Brown-eyed? (Use the Punnett
square method you learned in topic 33-3)
2. A tall pea plant (Tt) is crossed with a short pea plant (tt). What fraction of their
offspring would you expect to be tall? Note that tall is dominant and shortness is
recessive. (Use the square method)
3. Cross a white guinea pig Ww with another white guinea pig Ww. Both parents carry
a gene for blackness (w) which is not expressed. ln other words, both are
heterozygous. Use the square method and answer the following:
3 a. What fraction of the F1 offspring will be white? What % white?
3 b. What fraction will be black? What %?
3 c. What fraction of each genotype will you get? What % of each genotype?
3 d. What fraction of each phenotype wilt you get?
4. ln shorthorn cattle, some are red, some are white and others are roan. Roan is close
to pink in color. Neither red nor white is dominant. For this reason, the symbols
used to represent these animals are generally different. Use the following
genotypes to work out the problems that follow:
Neither red nor white is dominant. Cross a red cow
with a white bull. Give the fraction and each color of
offspring possible from this mating.
5. Cross a roan bull with a white cow. Give the colors and fractions for all possible
otfspring.
Before handing in your work, re-read the instructions at the beginning of this topic and
be sure you followed them exactly. Be sure you circled all of your answers.
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Applying the Principles of Genetics
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33-5 Hybrid Cross Problem Set
Objectlve
You will be expected to apply the principles of solving hybrid crosses to the
problems that follow.
Answer the following on your own paper. Show your work or give an explanation for
your answer. Present all work NEATLY.
1.
Show all the possible genotypes from the following crosses: (indicate the fractions of
each genotype)
Gg XGg
Gg xgg
2. lf G in the above problem is green apples
and
g is red apples, what would
the
fractions of each phenotype be in the two crosses in the above problem?
3. A brown-eyed mother and a blue-eyed
father found that their first child was blueeyed. What is the genotype of the mother? (The exact genotype)
4. What is the 7" chance that the couple in problem #3 would have a second child that
has brown eyes?
5. ln cats, assume that a spotted coat is dominant to a white coat. A white mother cat
gives birth to two white kittens and two spotted kittens. What are the genotypes and
phenotypes of the father cat?
6. A man with blue eyes marries
a brown-eyed woman whose mother had blue eyes.
What portion of the children would be expected to have blue eyes? Show the
genotypes of all people involved.
CIRCLE
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all answers on your paper.
Applying the Principles of Genetics
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