Download Punnett Worksheet

Punnett Worksheet
1. Let’s say that in seals, the gene for the length of the whiskers has two alleles. The
dominant allele (W) codes for long whiskers & the recessive allele (w) codes for short
whiskers.
(a) What percentage of offspring would be expected to have short whiskers
from the cross of two long-whiskered seals, one that is homozygous dominant and one
that is heterozygous?
(b) If one parent seal is pure long-whiskered and the other is
short-whiskered, what percent of offspring would have short whiskers?
2. In purple people eaters, one-horn is dominant and no horns is recessive. Draw a
punnett square showing the cross of a purple people eater that is hybrid for horns with
a purple people eater that does not have horns. Summarize the genotypes &
phenotypes of the possible offspring.
3. Mendel found that crossing wrinkle-seeded plants with pure round-seeded plants
produced only round-seeded plants. What genotypic & phenotypic ratios can be
expected from a cross of a wrinkle-seeded plant & a plant heterozygous for this trait?
4. A brown coat is dominant to a white coat in cattle. A farmer has a brown bull. How
would you determine whether the bull is a heterozygote for the dominant allele?
5. In humans, curly hair is dominant over straight hair. A woman heterozygous for hair
curl marries a man with straight hair and they have four children.
a) Show the parental cross and the possible gametes produced.
b) Use a punnett square to find the possible genotypes for the F1 generation.
c) What are the phenotypic and genotypic ratios of the F1?
d) What is the probability that the first child will have curly hair? What is the
probability that the third child will have curly hair?
6. a) Show the cross between a woman who is homozygous normal for vision and a man
who is homozygous for glaucoma. Glaucoma is dominant to normal vision.
b) If there are four grandchildren (F2 generation) all having parents (F1) with the
same genotype, how many of these children will have glaucoma?
c) What is the probability of each grandchild having glaucoma? What is the
probability of each child having normal vision?
7. Give the genotypic and phenotypic ratios of the possible offspring produced when a
heterozygous brown-eyed man marries a heterozygous brown-eyed woman. Brown
eyes are dominant over blue eyes which are recessive.
8. Two brown-eyed parents have two children with blue eyes. Give the genotypes of
each member of the family.
9. Albinism (lack of pigment) in humans is caused by a recessive gene. If normal
parents have an albino child, what is the probability that their next child will be
normal for pigment?
10. a) Free ear lobes are dominant to attached ear lobes in humans. If a homozygous,
recessive male marries a homozygous dominant female, what will be the
phenotypic and genotypic ratios of their offspring?
b) If one of these female children were to marry a man with her genotype, what would
be the phenotypic ratio of their children?
11. A homozygous, dominant individual for long eyelashes is crossed with a
heterozygous individual. What is the probability that they will produce offspring
without long eyelashes? Long lashes are dominant; short lashes are recessive.
12. The ability to taste the drug phenyl-thio carbamide (P.T.C.) is due to a dominant
gene. A non-taster man marries a taster woman whose father was a non-taster.
a) What will be the expected genotypes of their four children?
b) What would be the expected phenotypes for ten children?
c) What is the probability that their first child has the heterozygous genotype?
d) What could have been the genotype of this woman’s father?
13. Polled (hornless) condition in cattle is dominant over horned condition. A polled
bull is bred to three cows with the following results:
Cow A (horned) = polled calf
Cow B (horned) = horned calf
Cow C (polled ) = horned calf
a) What are the genotypes of the four parent animals?
b) What further offspring would you expect these matings might have produced?
14. In a certain strain of mice, black coat (B) is dominant over white coat (b). Describe
what you would do to determine the genotype of a male with a black coat.
DIHYBRID
In fruit flies (Drosophila), long wings (L) is dominant over short wings (l), and gray body
color (G) is dominant over ebony body color (g). Two long-winged, gray-bodied flies
mate with each other. Both flies are dihybrids – they are heterozygous for both traits.
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What is the genotype of the female fly?
What is the genotype of the male fly?
What are the possible gametes from these flies?
Draw the punnett square, and combine the gametes to produce offspring.
How many long-winged, gray-bodied offspring are there?
How many long-winged, ebony-bodied offspring are there?
How many short-winged, gray-bodied offspring are there?
How many short-winged, ebony-bodied offspring are there?
What is the phenotypic ratio of these offspring?