Name_______________________
Lab 7 – Genetics Problems
The primary difficulty most people have with genetics problems or story problems in general, is that they don’t
approach solving them in an organized fashion. Poor problem solvers can become good problem solvers by
practicing a simple organizational approach. I have set up the first few problems to introduce you to this
approach. WRITE EVERYTHING DOWN! Indulge me! The steps are not just busy work.
1. In peas, yellow flower color is dominant to green. What colors and proportions of offspring would
result from a cross between a heterozygous yellow plant and a homozygous yellow plant?
What color and the proportions of those colors would you get:
2. Cystic fibrosis is a common recessive disorder. What is the probability that two normal parents, both of
whom are heterozygous for cystic fibrosis, will have an affected child?
Probability of having an affected child:________%
3. Huntington’s disease results from the presence of a dominant allele and the disease does not show up
until middle age (40's).
a) How could two unaffected parents in their 20’s have children with Huntington’s? Why or
why not?
b) What is the possible genotypes of parents with Huntington’s: __________________
c) What is the likelihood of a child having Huntington’s if only one parent is diagnosed with the
disease?
Probability of having an affected child:________%
4. In humans, pigmented (brown) eyes are dominant over unpigmented (blue) eyes. A man with blue eyes
has both brown-eyed parents. The man’s wife is brown-eyed; her father was brown-eyed and her
mother was blue-eyed. The man and woman have a blue-eyed child.
a) What is the genotype of the husband:___________________________________
b) What is the genotype of the women’s father:_____________________________
c) What is the genotype of the women’s mother:____________________________
d) What is the genotype of the child’s:____________________________________
e) What is the genotype of the wife:______________________________________
f) Of questions a-d which were needed to figure out e?_______________________
5. In shorthorn cattle, a cross between homozygous red-coated (RR) cattle and homozygous white-coated
(WW) cattle produces roan-coated cattle (a pinkish color) (RW).
a) If a white-coated bull is bred to a red cow, what will be the phenotypes and genotypes of the F1?
b) If two F1 are mated, what will be the phenotypes and proportions of the F2?
Phenotypes and proportions of the F2:_____________________
c) What type of inheritance pattern is this? ________________________________________
6. When chickens with white feathers are crossed with black-feathered birds, their offspring’s feathers are
all slate blue. When blue are crossed among themselves, they produce white, blue, and black offspring
in the ratio of approximately 1:2:1, respectively.
a) What type of inheritance pattern does feather trait follow?_________________________
b) What phenotypes and genotypes would you expect from a cross of a white with a blue chicken?
Phenotypes and proportions:______________________
Genotypes and proportions:_______________________
7. In humans, brown eyes are dominant over blue eyes, and right-handedness is dominant over lefthandedness. A homozygous brown-eyed, homozygous right-handed man marries a blue-eyed, lefthanded woman.
a) What is the genotype of the father?_____________________
b) What is the genotype of the mother?____________________
c) What will be the phenotypes of the F1 generation?
Phenotypes of the F1 generation:__________________
d) Did you need to fill in the entire punnett square to answer this question? Why or why not?
e) If one of the members of the F1 generation marries a person of identical genotype, what will be the
phenotypic ratio of the offspring?
Phenotypic ratio of the offspring:
______________________________
______________________________
f) A brown-eyed, right-handed man marries a blue-eyed, right-handed woman. Their first child is
blue-eyed and left-handed.
What is the genotype of the father:_________________
What is the genotype of the mother:________________
8. In tomatoes, red fruit is dominant over yellow fruit while tall vines are dominant over short vines. A
tomato breeder has pure (homozygous) races of yellow-fruited, tall plants and red-fruited, short plants:
a) If the breeder crosses the two races that he has, what will be the appearance of the F1?
_____________________
b) Will the F1, when crossed, be able to produce a pure red-fruited, tall plant? Why? (you may need a
16 square punnett square for this if you can’t figure out the answer by thinking it through).
9. A freckled, blue-eyed man marries a brown-eyed woman without freckles. They have six children:
Two were blue-eyed without freckles, one blue-eyed with freckles, two brown-eyed with freckles, and
one brown-eyed without freckles. What are the genotypes of the parents and children (assume having
freckles is dominant)?
a) What are the possible genotype(s) of the blue-eyed without freckles children: ________________
b) What are the possible genotype(s) of the blue-eyed without freckles child: ___________________
c) What are the possible genotype(s) of the brown-eyed with freckles children: _________________
d) What are the possible genotype(s) of the brown-eyed without freckles child: _________________
e) What are the possible genotypes of the father: ________________________________
f) What are the possible genotypes of the mother: _______________________________
g) Now that you know all the possible genotypes go through and determine the children’s genotypes
now that you know the possible genotypes from the parents:
What is the genotype of the blue-eyed without freckles children: ________________
What is the genotype of the blue-eyed without freckles child: ___________________
What is the genotype of the brown-eyed with freckles children: _________________
What is the genotype of the brown-eyed without freckles child: _________________
10. A certain type of deaf-mutism is recessive. Assuming right-handedness is dominant to left-handedness:
a) A man and women who are both able to hear and are right-handed have a child who is a left-handed
deaf-mute.
What is the phenotype of the father:_____________________
What is the phenotype of the mother:____________________
b) What are the chances that their next child will be left-handed and normal?
Chances of their next child being left-handed and normal:
__________________
11. Human skin color is determined by the influence of at least three genes. The lightest possible skin color
is represented by all recessive alleles (aabbcc); the darkest skin color is represented by all dominant
alleles (AABBCC). Varying degrees of skin color are represented by all other genotypes. If a woman
of lightest skin color (aabbcc) marries a man with an intermediate skin color (AaBbCc):
a) Could they have a child that has darker skin than either parent? Explain.
b) Could they have a child that has lighter skin than either parent? Explain.
12. In humans, red/green color blindness is a sex-linked, recessive trait carried on the X chromosome. If a
normal vision man marries a heterozygous normal vision woman:
a) Since this is an X-linked trait how many copies of this allele does a man have:__________
b) How many copies of this allele does a man have:__________
c) What percentage of the couples boys would be expected to be color blind:__________
d) What percentage of girls would be expected to be color blind:___________________
e) What percentage of the girls would you expect to be carriers:___________________
13. John is the only member of his family with hemophilia (sex-linked recessive disorder carried on the X
chromosome).
a) What is John’s mother’s genotype:________________________
b) What is John’s father’s genotype:_________________________
c) What are the chances that a newborn brother will also be hemophilic? Explain.
14. Male cats may be black or yellow, while female cats may be black, yellow, or tortoise-shell (black and
yellow patches). The coat color in cats is sex-linked on the X chromosome. You cross a yellow female
and black male.
a) What are the phenotype(s) expected of the offspring male offspring:________________________
b) What are the phenotype(s) expected of the offspring female offspring:______________________
15. You have rabbits with three different color types: black, gray and white. You make the following
crosses and obtain the following results:
Cross
Gray x white
Gray x black
Black x white
Offspring
20 gray and 16 white
20 gray and 25 black
22 gray
Total # of Offspring
36
45
22
a) What are the phenotypes and percentages of the offspring when you cross two black rabbits:
______________________________________________________
b) What are the phenotypes and percentages of the offspring when you cross two white rabbits:
______________________________________________________
c) What are the phenotypes and percentages of the offspring when you cross two gray rabbits:
______________________________________________________
d) Compare your predictions to the gray x gray cross results actually obtained:
98 black
201 gray
103 white
Do your predictions come close to the observed results (do your percentages from c predict the results
from d)? If so, you understand the pattern of inheritance illustrated here!!