Download Simple Mendelian Genetics Problems

Name ________________________________________ Date __________
lAP Biology Genetics Problem Set
Simple Mendelian Genetics Problems
In peas, seeds may be round (R) or wrinkled (r).
1. What proportion of the offspring in the following crosses would probably
be wrinkled?

RR x rr

Rr x Rr

Rr x rr
2. In mice, the ability to run normally is a dominant trait. Mice with this trait
are called running mice (R). The recessive trait causes mice to run in
circles only. Mice with this trait are called waltzing mice (r). Hair color is
also inherited in mice. Black hair (B) is dominant over brown hair (b).
 Cross a heterozygous running, heterozygous black mouse with a
homozygous running, homozygous black mouse. List the parental
genotypes and the possible offspring genotypes with percentages.
3. Explain the difference between incomplete dominance and codominance.
AP Genetics Problem Set
1
Name ________________________________________ Date __________
Codominance
4. In some chickens, the gene for feather color is controlled by codominance.
The allele for black is B and the allele for white is W. The heterozygous
phenotype is known as erminette. (Erminette fowls have mostly light-colored
feathers with an occasional black one, giving a flecked appearance –both black and white
are on the feathers.)



What is the genotype for black chickens? ____
What is the genotype for white chickens? ____
What is the genotype for erminette chickens? ____
5. If two erminette chickens were crossed, what is the probability that:
 They would have a black chick? ____%
 They would have a white chick? ____%
6. In a maternity ward, four babies become accidentally mixed up. The ABO
types of the four babies are known to be O, A, B, and AB. The ABO types
of the four sets of parents are determined. Indicate which baby belongs to
each set of parents: (a) AB × O, (b) A × O, (c) A × AB, (d) O × O.
Incomplete Dominance
7. In humans straight hair (SS) and curly hair (CC) are traits, that result in
hybrids who have wavy hair (SC). Cross a curly hair female with a wavy
haired male. List the genotypes and phenotypes of the offspring.
AP Genetics Problem Set
2
Name ________________________________________ Date __________
8. In snapdragons, flower color is controlled by incomplete dominance. The two
alleles are red (R) and white (W). The heterozygous genotype is expressed as
pink.
 What is the phenotype of a plant with the genotype RR? ________
 What is the phenotype of a plant with the genotype WW? ________
 What is the phenotype of a plant with the genotype RW? ________
 Cross a RW X WW and list the genotypes and phenotypes.
Sex Influenced
9. Baldness in humans is a dominant, sex-influenced trait. This gene is on
the autosomes, not the sex chromosomes. A man who is BB or Bb will be
bald and will be normal only if he is bb. A woman will only be bald if she is
BB and normal if she is Bb or bb (it’s almost like B is dominant in males
and b is dominant in females). If two parents are heterozygous for
baldness, what are the chances of their children being bald? Use a
Punnett square to illustrate this. Note: because the sex of a person does
make a difference in how the gene is expressed, you need to set this up
as a dihybrid cross to account for the sex of the children (XX and XY).
Male BB & Bb = Bald
bb = not bald
Female BB = bald Bb & bb = not
Sex-Linked
AP Genetics Problem Set
3
Name ________________________________________ Date __________
10. The inheritance of color blindness in humans is due to a recessive gene
located on the X chromosome (X linked).
X+ (normal) or Xc (color blind)

If a color-blind boy is born to parents both of whom have normal
vision, what are the genotypes of the three individuals? HINT: You are
using X and Y chromosomes with superscripts on the X because sex of the
individual makes a difference.
Multiple Alleles
11. Another type of non-Mendelian trait is multiple alleles. Human hair color is
controlled by one gene with four alleles (with some incomplete
dominance):
HBr = brown HBd = blonde hR = red hbk = black
The possible genotypes and phenotypes:
 HBdHBd or HBdhbk = blonde
 HBdHBr = mousy brown
 HBdhR = strawberry blonde
 HBrHBr or HBr hbk = brown
 HBrhR = auburn hRhR or hRhbk = red hbkhbk = black

If someone with auburn hair has children with someone with red hair (but whose
mother had black hair), what are the genotype and phenotype probabilities for
their children?
AP Genetics Problem Set
4