Download Monohybrid Problems .I. Yellow coat color in guinea pigs is

Monohybrid
I.
Problems
. I.
In rabbits the allele for black coat color (B) is dominant over the allele for brown coat color
(b). What is the genotypic ratio and phenotypic ratio be for a cross between an animal
homozygous for black coat color and one homozygous for brown coat color?
2.
In humans hair texture is controlled by incomplete dominance. A curly haired individual and a
straight haired individual have all wavy haired children. If two wavy haired people have
children, what will the phenotypic ratio be?
3.
In Japanese four o'clock flowers, color is inherited by genes that show incomplete
dominance. In such flowers, a cross between a homozygous red flower and a homozygous
white flower will always result in pink flowers.
2. White (JV) hair in sheep is caused by the dominant gene while black (w) hair is recessive. A
heterozygous white male and a black female are parents of a black lamb. What is the
probability that their next lamb will be white? What are the genotypic and phenotypic ratios?
3. Albinism is recessive in humans. An albino man marries a woman who is not albino, but had
an albino father. What is the probability of this couple having a child that is not an
albino? What are the genotypic and phenotypic ratios?
4. Todd and Melissa are college students who are planning to get married. They are currently
taking a genetics course and decided to determine the eye color of any possible children they
might have. Blue eyes are recessive to brown eyes. Todd has brown eyes, like his three
brothers. His mother and grandmother have blue eyes, but his father and all other grandparents
have brown eyes. Brown eyed Melissa has one blue eyed sister and one brown eyed sister and a
mother with blue eyes. Her father and all of her grandparents have brown eyes. Construct an
accurate punnett square to determine the possible eye colors of their yet to be born
children. What are the genotypic and phenotypic ratios?
5. In Teenage Mutant Ninja Turtles, green shells are dominant over brown shells. Leonardo, who
is heterozygous for a green shell, marries the lovely Mona Lisa, who has a brown shell. What
are the genotypic and phenotypic ratios?
6.
In humans, polydactyly (an extra finger on each hand or toe on each foot) is due to a dominant
gene. When one parent is polydactylous, but heterozygous, and the other parent is normal, what
are the genotypic and phenotypic ratios of their children?
Di-hybrid Problems
I.
In human, aniridia, (a type of blindness resulting from absence of an iris) is due to a dominant
gene. Migraine (a sickening headache) is due to a different dominant gene. A man with aniridia,
whose mother was not blind, marries a woman who suffers from migraine. The woman's father
did not sutTer from migraine. In what proportion of their children would both aniridia and
migraine be expected to occur?
a. A cross is made between two pink flowers. What is the probability for each
phenotype?
b. What is the genotypic and phenotypic ratio for a cross between a plant with red
flower and a plant with pink flowers? .
c. A plant breeder wants to produce only pink Japanese four o'clock flowers. Can he
do so by crossing pink Japanese four o'clock flowers with white Japanese four
o'clock plants? Use a punnett square to support your answer.
4. Hair texture in humans is incompletely dominant. Curly hair plus straight hair gives you wavy
hair. Also, having 2 eyebrows is dominant over one eyebrow. If two individuals are
heterozygous for both traits, what is the probability of each phenotype in their future offspring?
5. Remember that hair texture is incompletely dominant. Widow's peak is dominant to not having
a window's peak. If a couple has wavy hair and both do not have a widow's peak, what is the
phenotypic probability of their children?
Co-dominance
I.
In watermelons, solid green color (G) is dominant over striped pattern (g), and short shape (S) is
dominant over long shape (s). What is the probability of each phenotype of possible offspring if
a heterozygous solid, long watermelon cross pollinates with a heterozygous solid, heterozygous
short watermelon?
3. Having two eyebrows is dominant (E) over having one large eyebrow (e). Also having six
fingers (F) is dominant over having five fingers (f). What is the probability of each phenotype if
a man that has one eyebrow and twelve fingers total (heterozygous), has children with a woman
that is heterozygous for both traits?
Problems
In shorthorn cattle, the hybrid between red and white is roan, having red and white hairs
intermingled. If a roan is bred with a white, what will the phenotypic ratio be?
Multiple Allele Problems
I.
2.
Yellow coat color in guinea pigs is produced by the homozygous genotype, YY, and cream
color by the heterozygous genotype, Yy. White is produced by the homozygous genotype,
yy. What genotypic ratios are produced by matings between cream colored guinea
pigs? Describe the phenotypic ratio.
Suppose a man with homozygous A blood marries a woman with AB blood. What blood types
would you expect to find among their children?
2. A man of type AB blood is married to a woman of type 0 and he questions the legitimacy of
her child, who has type 0 blood. What should the legal judgment be?
3. A child has blood type AB, and the mother has blood type A.
a. What are the possible genotypes of the child's father?
b. Could the father be type O? Explain.
Incomplete Domluance Problems
4. Mrs. Doe and Mrs. Jones had babies at the same hospital at the same time. Mrs. Doe took home
a girl and named her Nancy. Mrs. Jones received a boy and named him Richard. However, Mrs.
Jones was sure she had had a girl and brought a law suit against the hospital. Blood tests
showed the Mr. Jones was type O. Mrs. Jones was type AB. Mr. and Mrs. Does were both type
A. Nancy was type B and Richard was type O. Had an exchange occurred? Explain!
5. Mike and Carol Brady are expecting their first child together. Mike, however, has noticed that
Sam the Butcher has been hanging around the house at weird times and often when Alice is not
around. When baby Brady is born, Mike notices that its blood type is B+. Mike is concerned
because he has AB- blood and Carol has 0+ (heterozygous positive). Sam the butcher has A+
(heterozygous positive) blood. Is Mike just being sill and as normal will they have this situation
settled in 30 minutes, or will the show be continued for paternity suits?
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GENETICS PROBLEMS: Include the appropriate Punnett Squares to demonstrate how you
answered each problem or receive no credit. Some of the problems are taken from the end of
chapter exercises or the website.
I. In peas, tall plants are dominant to short plants. Complete a punnett square to show the
genotypes and phenotypes expected for the following cross: heterozygous tall x
heterozygous tall
2. In humans, the gene for brown eyes (b) is dominant to the gene for blue eyes and the gene
for right handedness (r) is dominant to the gene for left handedness. Two individuals
heterozygous for both of these characteristics marry.
A. Complete a punnett square to show the expected genotypes and phenotypes of the
offspring.
B. Summarize the ratio of the phenotypes
3. In chimpanzees, straight fingers are dominant to bent fingers. Complete a punnett square to
show the genotypes and phenotypes expected for the following cross: heterozygous straight
x homozygous bent
4. In four o'clock flowers, red plants are homozygous for the allele (R) of the gene for flower
color. Plants with white flowers are homozygous for the (r) allele of the same gene. Plants
with pink flowers are are heterozygous for these two alleles. Complete a punnett square to
show genotypes and phenotypes that are expected when plants with pink flowers are
intercrossed.
5. The long hair of persian cats is recessive to the short hair of siamese cats, but the black coat
of persians is dominant to the brown and tan coat of siamese. Mating of persians with
siamese cats produces an fI generation heterozygous for both of these characteristics.
Complete a punnett square to show the expected genotypes and phenotypes of the offspring
from the mating of these fl heterozygous cats.
6. As in labrador retrievers, fur color in mice is governed by genes concerned with producing
and distributing melanin. At one gene location, a dominant allele (b) specifies dark brown
and a recessive gene (b) specifies a tan coat. At another gene location, a dominant allele
permits melanin production and a recessive allele (c) shuts it down, resulting in the
production of an albino mouse. Complete a punnett square to show the expected phenotypes
and genotypes resulting from crossing a true breeding brown mouse with an albino mouse
that is homozygous recessive for both genes. (5 points)
7. Complete a punnett square to show expected the phenotypes and genotypes resulting from
interbreeding the the offspring produced in the above experiment (5 points)
8. The x-linked barred locus in fruit flies controls the pattern of the wings, with the alleles (b)
for barred pattern and (b) for no bars. A male with barred wings is mated to a non-barred
female. Complete a punnet square to show the expected genotypes and phenotypes of the
offspring
9. Muscular dystrophy is a sex-li~ked recessive disorder. A man with muscular dystrophy
marries a woman who does not have this disease. Half of their daughters and half oftheir
sons develop this disease. What is the genotype of the father? The mother? Document how
you arrived at your answer or receive no credit
10. Colorblindness is a sex-linked recessive character. A color blind woman marries a male with
normal color vision (c).
A. What are the genotypes of each?
B. Complete a punnett square to show what the expected average phenotypes and
genotypes of their offspring will be .
II. In radishes, two incompletely dominant genes control color and shape. Red and white
radishes are homozygous, whereas the hybrid is purple. Long and round radishes are
homozygous and if crossed will produce an oval hybrid. Complete a punnet square to show
the genotypes and phenotypes produced by crossing pure breeding red long radishes with
white round radishes.
12. Suppose you identify a new gene in mice. One of its alleles specifies white fur color. A
second allele specifies brown fur color. You want to determine whether the relationship
between the alleles is simple dominance (and if so which color is dominant) or incomplete
dominance. What sorts of genetic crosses would give you the answer? On what types of
observations would you base your answers?
o Hint: Cross true breeding brown and white mice and and then interbreed their
offspring. TO OBTAIN CREDIT YOU MUST draw the Punnett-squares for the FI
and F2 generations of each of the three different possibilities.
13. A women with type A blood has a child with type 0 blood. She is suing a man with type B
blood for child support, because she claims that man is the father of her child. How would
you respond to the following statements.
The attorney for the alleged father claims "The mother's blood is type A, so the
child's type 0 blood must have come from the father. Because my client has type B
blood, he can not be the father." Justify your answer with appropriate Punnettsquare(s) or receive 0 points!
A. The attorney for the mother claims "Because further tests prove he is heterozygous,
he must be the father."
14. Suppose expression of one allele of a Y-linked gene results in nonhairy ears in males.
Expession of another allele results in rather long hairs, a condition known as hairy pinnae.
Why would you NOT expect females to have hairy pinnae. Justify your answer with
appropriate Punnett-square(s) or receive 0 points!
A. A son of a hairy-eared male will also be hairy-eared. Explain why. Justify your
answer with appropriate Punnett-square(s) or receive 0 points!
15. In the figure (a pedigree diagram similar to figure 12.11), does the phenotype indicated by
the dark circles and squares follow autosomal dominant, autosomal recessive or sex-linked
(X recessive) inheritance? Explain fully why or why not for each of the three. Include the
appropriate Punnett Squares to demonstrate the inheritance pattern expected for each of the
three.
16. Use Punnett-squares to show genotypes and phenotypes or receive 0 points!
Kernel color in wheat plants is determined by two pairs of genes. Alleles of one pair
show incomplete dominance over the other pair.
A. For the gene pair at one locus on the chromosome, allele Al imparts one dose of red
color to the kernel, whereas allele A2 does not. At the second locus allele B 1 gives
one dose of red color to the kernel, whereas 82 does not. One kernel with genotype
AIAI81BI is dark red. A different kernel with genotype A2A28282is white. All other
genotypes have kernel colors in between the two extremes.
B. Suppose you cross a plant grown from a dark red kernel with a plant grown from a
white kernel. What g6notype8 and phenotypes would you expect among the
offspring?
C. If a plant with genotype AIA28182selffertilizes, what genotypes and phenotypes
would you expect among the offspring? In what proportions?
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