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Genetics Practice Problems
1. For each genotype below, indicate whether it is heterozygous (He) or homozygous (Ho)
AA _____
aa ______
Pp ______
pp ______
Aa ______
BB ______
2. For each of the genotypes below determine what phenotypes would be possible.
Red eyes are dominant to white, Tall plants are dominant to short.
RR ______
Rr ______
rr ______
TT ______
Tt ______
tt ______
3. For each phenotype below, list all of the possible genotypes (remember to use the letter of the
dominant trait)
Brown fur is dominant to white, purple flowers are dominant to white.
Brown fur _________________
White fur ________________
Purple flowers ___________________
White flowers ___________________
Use a Punnett Square to solve the following problems:
4. A guinea pig with short hair (SS) is bred to a guinea pig with long hair (ss). How many of the
offspring will have short hair? Show your work.
5. In pea plants purple flowers are dominant to white. Two heterozygous, purple flowered pea
plants are crossed. What is the genotypic ratio? Show your work.
6. Round peas are dominant to wrinkled in pea plants. You have a plant that produces round peas,
but you do not know the genotype. You perform a testcross and get 50% round and 50% wrinkled
peas. What is the genotype of the round-seeded parent? Show the testcross.
7. Two purple flowered pea plants are crossed together. Out of 100 offspring, 25 are white. What
are the genotypes of the parents? Show your work.
The following problems deal with two traits – use the 16-square Punnett Square!
In rabbits, grey hair is dominant to white hair.
Also in rabbits, black eyes are dominant to red eyes.
KEY:
GG = gray hair
Gg = gray hair
gg = white hair
BB = black eyes
Bb = black eyes
bb = red eyes
8. What are the phenotypes (descriptions) of rabbits that have the following genotypes:
Ggbb ____________________ ggBB ________________________
ggbb ____________________ GgBb _________________________
9. A male rabbit with the genotype GGbb is crossed with a female rabbit with the
genotype ggBb The square is set up below. Fill it out and determine the phenotypes and
proportions in the offspring.
How many out of 16 have grey fur and black
eyes? ______
How many out of 16 have grey fur and red
eyes? ________
How many out of 16 have white fur and
black eyes? ______
How many out of 16 have white fur and red
eyes? _______
10. A male rabbit with the genotype GGBb . Determine the types of gametes produced by
this rabbit (the sperm would have these combinations of alleles) Hint there are 4
combinations.
11. A female rabbit has the genotype GgBb. Determine the types of gametes (eggs)
produced by this rabbit.
12. Use the gametes from #10 and #11 to set up the Punnett square below. Put the male's
gametes on the top and the female's gametes down the side. Then fill out the square and
determine what kind of offspring would be produced from this cross and in what
proportion.
13. An aquatic arthropod called a Cyclops has antennae that are either smooth or barbed.
The allele for barbs is dominant. In the same organism, resistance to pesticides is a
recessive trait. Make a "key" to show all the possible genotypes (and phenotypes) of this
organism. Use the rabbit key to help you if you're lost.
Key:
14. A Cyclops that is resistant to pesticides and has smooth antennae is crossed with one
that is heterozygous for both traits. Show the genotypes of the parents.
______________ x _______________
15. Set up a Punnett square for the cross.
16. What are the phenotypic ratios of the offspring?
Use the following list of traits for ball pythons for the next set of questions:
Albino is a recessive mutation (a)
Piebald is a recessive mutation (p)
Pinstripe is a dominant mutation (S)
17. An albino heterozygous for piebald is crossed with a piebald heterozygous for albino.
What are the genotypes of the parents?
18. Show the cross:
19. A pinstripe het for albino is bred to a normal patterned albino. The offspring are all
pinstriped. What are the genotypes of the parents?
20. Show the Punnett Square and ratio of phenotypes that result from this cross.
Extra Credit: If you cross a heterozygous pinstripe heterozygous for both albino and
piebald and a normal pattern albino het for piebald, what is the probability of getting a
hatchling that shows all three traits?