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Mendel,
Genotypes and
Phenotypes
Punnett
Squares
Pedigrees
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Meiosis
Non-Mendelian
Inheritance
$100 Question: Meiosis
What is crossing over? During which
phase of meiosis does crossing over
take place?
$100 Answer: Meiosis
Crossing over is when homologous
chromosomes swap segments of DNA.
Crossing over occurs during prophase I (or
prometaphase I) of meiosis.
$200 Question: Meiosis
A crayfish cell has 200 total or 100 pairs of chromosomes.
Following mitosis, the daughter cells would each have a
total of ______ chromosomes. After meiosis, the four
daughter cells would have _____ chromosomes.
a. 200, 200
b. 100, 100
c. 100, 200
d. 200, 100
e. 46, 23
$200 Answer: Meiosis
d. 200, 100
$300 Question: Meiosis
Compare and contrast the daughter cells
produced by meiosis to the parent cell in
terms of:
-Number of cells.
-Chromosome number.
-Composition of chromosomes.
-Purpose of cells.
$300 Answer: Meiosis
Parent cell
-1 cell
-2n (diploid), in humans – 46.
-Chromosomes have not gone through crossing over, so maternal and
paternal chromosomes are separate.
- Cells generate sex cells, gametes, sperm or eggs, etc.
Daughter cells
-4 cells
-1n (haploid), in humans – 23.
-Chromosomes have gone through crossing over so maternal and
paternal chromosomes have a mix of DNA; also, chromosomes have
been assorted independently.
-Cells are sex cells, gametes, sperm or eggs, etc.
$400 Question: Meiosis
How are the processes of meiosis and
fertilization shown in Punnett squares?
How do Punnett squares illustrate
Mendel’s laws of independent assortment
and segregation?
$400 Answer: Meiosis
Punnett squares show meiosis through the
separation of alleles (Bb being separated
into B and bs, for instance) – which is
Mendel’s law of segregation – and in alleles
assorting independently of one another
(BbTt forming four kinds of gametes) –
which is Mendel’s law of independent
assortment.
$500 Question: Meiosis
Disorders like Down Syndrome, Trisomy 13
Syndrome, etc. result when the zygote ends up with
aneuploidy – an abnormal number of chromosomes.
Plants sometimes end up polyploid – having a 3n or
4n chromosome number, which can found a new
species of plant.
Given what you know about meiosis, propose how
both aneuploidy and polyploidy result.
$500 Answer: Meiosis
Anueploidy and polyploidy both result from non-disjunction,
when chromosomes fail to divide properly in meiosis.
Aneuploidy generally results when one set of homologous
chromosomes (for instance, chromosome 21 in the case of Down
syndrome) fails to separate in anaphase I of meiosis. The
resulting gametes have an abnormal number (22 or 24) of
chromosomes.
In plants, an entire set or sets of homologous chromosomes fail
to separate, leading to gametes that are 2n or 3n, resulting in 3n
or 4n offspring. (Or two plants can do this, each with 2n
gametes, etc.) This results in plants having high chromosome
numbers and sometimes the formation of a new species.
$100 Question: Mendel,
Genotypes, and Phenotypes
What is the difference between a
genotype and a phenotype?
$100 Answer: Mendel,
Genotypes, and Phenotypes
Genotypes refer to an organism’s internal
genetic code; phenotypes refer to an
organism’s external appearance or behavior.
$200 Question: Mendel,
Genotypes, and Phenotypes
Use the following traits to complete questions on
genotypes, phenotypes and Punnett squares.
Two Antennae (A) vs. One Antennae (a)
Pointy Ears (I) vs. Round Ears (i)
A male has the genotype AA and is heterozygous for
ear shape. His wife is heterozygous for antennae and
ii for ear shape. What will their phenotypes be?
$200 Answer: Mendel,
Genotypes, and Phenotypes
Him: Two antennae, pointy ears.
Her: Two antennae, round ears.
$300 Question: Mendel,
Genotypes, and Phenotypes
During Mendel’s experiments, he crossed a pea plant with smooth peas
with a pea plant with wrinkled peas. All the plants in the F1
generation had smooth peas. From this information, you can
conclude:
a. The smooth allele is dominant to the wrinkled allele because the
smooth allele hid the presence of the wrinkled allele.
b. The smooth and wrinkled alleles are codominant to each other.
c. The smooth and wrinkled alleles are incompletely dominant to
each other.
d. The wrinkled allele is dominant to the smooth allele because the
wrinkled allele was hidden by the smooth allele.
$300 Answer: Mendel,
Genotypes, and Phenotypes
a.
The smooth allele is dominant to the wrinkled
allele because the smooth allele hid the presence
of the wrinkled allele.
$400 Question: Mendel,
Genotypes, and Phenotypes
An experimenter wants to determine if
a plant with purple flowers is
homozygous dominant or heterozygous
for the trait. Purple flowers are
dominant to white flowers. Design an
experiment that would determine which
genotype the plant has.
$400 Answer: Mendel,
Genotypes, and Phenotypes
Cross the plant with purple flowers with a
plant with white flowers, which are always
homozygous recessive. If half the offspring
are white, the plant is heterozygous. If all the
offspring are purple, then the plant is
homozygous dominant.
$500 Question: Mendel,
Genotypes, and Phenotypes
Both pink and blue hydrangeas have the same genotype
for flower color. Explain how the same genotype can
produce two different flower colors.
$500 Answer: Mendel,
Genotypes, and Phenotypes
The hydrangea’s phenotypes are, in part, determined
by the soil in which they are planted. Pink flowers
result from acidic soils, blue flowers from basic soils
and intermediate (purple) flowers from more neutral
soils.
Just as environment (sunlight, fake tanning) can
influence phenotype in humans, it can also influence
phenotype in plants.
$100 Question: Punnett Squares
Perform the following cross: Ss x Ss.
(S= short fur, s= long fur.) What are the
genotypes and phenotypes of the
offspring?
$100 Answer: Punnett Squares
S
s
S
s
SS
Ss
Ss
ss
Genotypes: 25 percent homozygous dominant; 50 percent
heterozygous; 25 percent homozygous dominant
Phenotype: 75 percent short fur; 25 percent long fur
$200 Question: Punnett Squares
Hair color in humans is NOT sex-linked. Brown hair
(B) is dominant to blond hair (b). A blond-haired
woman has children with a male heterozygous for
hair color. What percentage of their offspring are
likely to have blond hair?
a.
0 percent
b.
25 percent
c.
50 percent
d.
75 percent
e.
100 percent
$200 Answer: Punnett Squares
c.
50 percent
$300 Question: Punnett Squares
Two parents heterozygous for two
traits mate and have children. How
many of their children are likely to be
homozygous dominant for both
traits?
$300 Answer: Punnett Squares
One out of sixteen.
AB
Ab
aB
ab
AB
AABB
AABb
AaBB
AaBb
Ab
AABb
AAbb
AaBb
Aabb
AaBB
AaBb
aaBB
aaBb
AaBb
Aabb
aaBb
aabb
aB
ab
$400 Question: Punnett Squares
An individual homozygous dominant for two traits
(unattached earlobes and brown eyes) has children with
an individual homozygous recessive for two traits
(attached earlobes and blue eyes). WITHOUT
performing a Punnett square, predict what the
genotypes and phenotypes of the offspring will be.
$400 Answer: Punnett Squares
All offspring will be heterozygous for
both traits and have unattached
earlobes and brown eyes.
$500 Question: Punnett Squares
A scientist crosses two plants heterozygous for two traits
and gets the following phenotypic ratios. Explain how
these numbers could be so different from the expected
phenotypic ratios.
$500 Answer: Punnett Squares
These genes are located on the same chromosome,
therefore they do not assort independently of one
another. These are known as “linked” genes. When
phenotypic ratios are significantly different from what
we expect with independent assortment, we can
conclude something else – such as gene linkage – may
be at work. Depending on how frequently genes assort
independently from one another, we can establish how
far away from each other they are on a chromosome.
$100 Question: Pedigrees
Two people in a pedigree are linked like
this:
What is the relationship between them?
$100 Answer: Pedigrees
They are married. You can tell by the
line connecting them.
$200 Question: Pedigrees
In the above pedigree, people with brachodactylia, a dominant trait,
are shaded in while people with a recessive trait are left blank.
Use a B for brachodactylia and a b for normal fingers. What are
the genotypes of II-8 and II-2? How do you know?
$200 Answer: Pedigrees
II-8 - bb, because the person is
homozygous recessive since his square
is unshaded
II-2 - Bb. The person must be
heterozygous, since her parents are Bb
and bb. To be shaded, she must have
the dominant trait and cannot be BB.
$300 Question: Pedigrees
The following pedigree shows the inheritance of a recssive
trait in a family. Those with the recessive trait are shaded in
red. What are the genotypes of I-1 and II-2? How do you
know?
$300 Answer: Pedigrees
I-1 is homozygous recessive he shows
the recessive trait. II-2 is heterozygous
because half her children are
homozygous recessive and half are
heterozygous.
$400 Question: Pedigrees
How would a pedigree of a sexlinked recessive trait differ from
a pedigree of a non-sex-linked
recessive trait?
$400 Answer: Pedigrees
A pedigree of a sex-linked recessive trait
would show more males that display the trait
than females. A pedigree of an autosomal
trait would show an equal number of males
and females with the trait.
$500 Question: Pedigrees
For the above pedigree, people with a trait have been shaded in. Is
this trait: Autosomal or sex-linked? Dominant or recessive? HOW
DO YOU KNOW?
$500 Answer: Pedigrees
The trait is dominant and can either be sex linked or
non-sex-linked. If it’s dominant, both parents are
heterozygous and the affected offspring are either
homozygous dominant or heterozygous.
If the trait is sex-linked, then the parents are XAY
and XAXa. The affected females are either
homozygous dominant or heterozygous for the trait.
The affected males are XAY.
$100 Question: Non-Mendelian
Inheritance
A red flower is crossed with a white
flower. The resulting offspring are all
pink. What kind of inheritance are these
flowers showing?
$100 Answer: Non-Mendelian
Inheritance
This is incomplete dominance because the
offspring resemble and intermediate of the
two parents.
$200 Question: Non-Mendelian
Inheritance
A rabbit with black and white hair breeds
with a rabbit with black and white hair.
25 percent of the resulting rabbits have
black hair, 50 percent have black and
white hair, and 25 percent have white
hair. What kind of inheritance is
displayed here? How do you know?
$200 Answer: Non-Mendelian
Inheritance
These rabbits are displaying
codominant inheritance. We know
because the rabbits can display two
dominant traits (black and white fur)
simultaneously.
$300 Question: Non-Mendelian
Inheritance
A woman with type A blood is married to
a man with type B blood. One of their
children has type A blood. The man
suspects that the child is not his
(genetically). Can the child be his?
SHOW YOUR WORK!
$300 Answer: Non-Mendelian
Inheritance
IAIA or IAi x IBi.
IA
IB
i
IAIB
IAi
IA
IAIB
IAi
IA
IB
i
I AIB
I Ai
i
IBi
ii
$400 Question: Non-Mendelian
Inheritance
The following pedigree shows the inheritance of color blindness
in a family. Color blindness is an X-linked recessive trait
represented by the symbol Xr. People who are colorblind are
represented by shaded boxes. Those who are not colorblind have
blank boxes. What are the genotypes for II-4 and III-4? How do
know?
$400 Answer: Non-Mendelian
Inheritance
II-4 is XRXr - We know because her son
is colorblind (XrY) and males receive
their X chromosome from their mother.
III-4 is XrY because he is male and
colorblind.
$500 Question: Non-Mendelian
Inheritance
People with red hair and pale skin often
experience more dental pain than people of
different hair colors and skin tones. Explain
what could make this correlation possible,
in terms of non-Mendelian genetics.
$500 Answer: Non-Mendelian Inheritance
Sometimes single genes can have multiple
effects. A mutation in the MCR1 gene can
lead to lack of brown pigmentation (red
hair comes from the red pigments showing
through). A mutation in the same gene can
increase likelihood of experiencing dental
pain. This kind of inheritance – one gene
with many effects – is called pleiotropy.