Download Monohybrid and Dihybrid Key

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Genetics Problem Pack
The following problems deal with many different
Some will be easy others may be very difficult.
of genetics problems to solve each problem.
real-world
genetics situations.
Remember to follow the basic rules
Follow these steps for EVERY
problem:
1. Define alleles
2. Define phenotypes associated
3. Write
with genotypes
out cross
4. Produce gametes
5. Perform cross (Punnett square)
6. Determine
genotypic and phenotypic
ratios of offspring
7. Use the above to answer the problem
Each Problem
=
5 pts.
All work shown and correct
3
=
=
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2
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5
4
All work shown, easy to follow and correct
All work shown and incorrect
1 = Only incorrect
o = Problem
answer given
answer given
not solved
Monohybrid Crosses:
1. Assume that white color is dominant over yellow color in squash. If pollen from the anthers
of a heterozygous white-fruited plant is placed on the pistil of a yellow-fruited plant, what
would be the ratios among the genotypes and among the phenotypes of plants grown from
the resulting seeds?
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2. In human beings, brown eyes are usually dominant over blue eyes. Suppose a blue-eyed man
marries a brown-eyed woman whose father had blue eyes. What proportion of their children
would you predict will have blue eyes? Note: The use of eye color as a simple Mendelian
inheritance is a simplification. For a better description of eye color inheritance see this link:
http://www.ncbi.nlm.nih.gov/omim/
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3. Ifa brown-eyed man marries a blue-eyed woman and they have 10 children, all with brown
eyes, can you be certain that the man is homozygous for eye color? If the eleventh child has
blue eyes, will that prove what the father's genotype is? Why?
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4. Sickle cell anemia is an autosomal recessive disorder caused by changing a single amino
acid in the protein hemoglobin. This hemoglobin becomes "sticky" when oxygen is low in
the blood and causes red blood cells to form a sickle shape and get stopped up in blood
vessels. It is most prevalent in African Americans. One in six hundred African Americans is
born with sickle cell anemia and 1112blacks carry the allele. An African American couple
comes in for genetic counseling, they are both carriers of sickle cell anemia (heterozygotes)
and they want to know the likelihood that their child could have sickle cell anemia. What do
you tell them? Support your answer by showing a cross. What is the likelihood that their
child would be a carrier? What is the probability that a child would not have the sickle cell
allele?
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5. Cystic brosis (CF) is a disorder that causes abnormal body secretions. Of particular concern
is heavy mucous in the lungs that makes the individual more susceptible to pneumonias and
other lung diseases. CF is the most common genetic disorder of whites of Northern
European ancestry, with about 1125carrying the allele for CF and 1/3000 white babies
having the disease. A normal couple has their first baby and it has CF. What is the
likelihood that a second baby born to this couple would have CF? Show all work below.
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Dihybrid Crosses:
1. In the fruit fly Drosophila melanogaster, vestigial wings and hairy body are produced by two
recessive alleles carried on different chromosomes. The normal alleles, long wings and
hairless body, are dominant. If a vestigial-winged, hairy male is crossed with a female
homozygous for both of the normal traits, what would be the phenotypes and genotypes of
their progeny? If the F I generation was allowed to mate randomly among themselves, what
phenotypes and genotypes would be expected among the F2'S, and in what proportions?
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2. If a hairy female heterozygous for vestigial wing is crossed with a vestigial-winged male
heterozygous for hairy body, what will be the characteristics of the FI generation?
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3. In peas, a gene for long stems (L) is dominant over its allele for short stems (I). The gene for
smooth seeds (W) is dominant over the allele for wrinkled seeds (w). Calculate the
genotypic and the phenotypic ratios that would be expected among the progeny of the
following crosses:
a) LLWW x llww
b) A F 1 cross from above
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for solid color. Another gene produces a fusion of the two hooves on each foot, a condition
known as syndactyly. The syndactyl allele is dominant over the allele that produces normal
hooves. If a solid-colored hog homozygous for syndactyly is mated with a normal-footed hog
homozygous for the belted character, what would be the genotypes and phenotypes of the
progeny? If the progeny are allowed to breed freely among themselves, what genotypes and
phenotypes would you predict among their offspring, and in what proportions?
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5. In watermelons, the genes for green color and for short shape are dominant over their alleles
for striped color and for long shape. If a plant producing long, striped fruit is crossed with a
plant that is heterozygous for both these characters, what would be the phenotypes of plants
grown from the resulting seeds, and in what ratios?
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6. A dominant gene, A, causes yellow color in rats. In another, independent gene, the dominant
form (R) produces a black coat color. When the two dominants occur together (A_R _), they
interact to produce grey. Rats with the genotype aarr are cream-colored. If a grey male and a
yellow female, when mated, produce a litter of five consisting of3/5 grey~
and 1/5 black individuals, what are the genotypes of the parents?
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