Download Punnett Square (and Pedigree) Practice

Punnett Square (and Pedigree) Practice
1. In seals, the gene for the length of the whiskers has two alleles. Long whiskers are
dominant, short whiskers are recessive. We use the letter “w” to describe whisker length.
a. Write the homozygous dominant genotype. __________
b. What is the phenotype for the genotype above (#a)? ___________
c. Write the heterozygous genotype. ______
d. What is the phenotype for the genotype above (#c)?________________
e. Write the homozygous recessive genotype.________
f. What is the phenotype for the genotype above (#e)?________________
g. In a cross between a homozygous dominant papa seal with a homozygous recessive mama seal, what
percentage of the offspring would be expected to have long whiskers?
h. In a cross of two heterozygous parent seals, what percentage of the offspring would be expected to
have short whiskers?
2. In purple people eaters, one-horn is dominant and no horns are recessive. A homozygous
dominant purple people eater mates with a no-horned purple people eater.
a. What are the genotype probabilities of the offspring? ________________
b. What are the phenotype probabilities of the offspring? _______________
3. In Gateway gators, blue is the dominant skin color (B), red is recessive (b). But a cross
between a blue gator & a red gator produces a purple gator (Bb).
a. What pattern of inheritance does this illustrate? ____________________
b. If a purple gator is crossed with a blue gator, what is the chance the baby will be red? ___________
4. In the ABO blood type system, there are three alleles - A and B are dominant, O is
recessive.
a. What pattern of inheritance does this show? _____________________
b. A woman with Type O blood and a man who is Type AB have are expecting a child. What are the
possible blood types of the kid? ________________________
c. A baby has type AB blood. His mom has type B blood. What are the possible genotypes of his
father? ______________________________
5. Hemophilia is a sex-linked, recessive trait, meaning that the allele is carried on the X
chromosome and people with a recessive genotype get the disease. A woman who is
heterozygous for the trait has a child with a man who does not have hemophilia.
a. What is the mom’s genotype? ______________
b. What is the dad’s genotype? __________
c. What is the mom’s phenotype? ___________________
d. What is the dad’s phenotype? ________________
e. What is the chance that the child will have hemophilia?
f. Assuming the couple has a son, what is the chance he will have hemophilia?
6. Huntington’s disease is a dominant disease. Individuals who are homozygous dominant and
heterozygous get the disease, but individuals who are homozygous recessive do not get the disease.
a. What are the genotypes of people who get Huntington’s disease? _________________________
b. Both parents are heterozygous for the Huntington’s allele. What is the chance that their child will not
have Huntington’s disease? _______________________________
c. What does this scenario suggest to you about the relationship between the dominant alleles and most
common alleles? (Hint – how many people do you know with Huntington’s) _______________________
7. Cystic Fibrosis is a recessive disease. Individual’s who are homozygous recessive build up fluid in
their lungs and struggle to breathe. Homozygous dominant and heterozygous individuals have no
symptoms of the disease.
a. People with this disease often don’t live long enough to reproduce and pass the allele on to their
offspring. Why does the allele still exist in the population? Why doesn’t it disappear? ______________
______________________________________________________________________________
b. Jack and Diane want to have a baby, but both have a history of cystic fibrosis in their families. Draw a
pedigree based on the following information.
- Jack has a brother with cystic fibrosis.
- Jack had a child in a previous marriage that was born with the disease.
- Jack’s parents and sister are all healthy
- Diane is an only child. Her parents are both healthy.
- Diane’s uncle (her mother’s brother) died of cystic fibrosis when he was 3 yrs old
c. Add genotypes of as many people as possible to the pedigree.
d. You are the genetic counselor that Jack and Diane go to see. What would you tell them about the
chances that their child would have cystic fibrosis? Would you suggest that they try and have a baby?
Or do you think the risks are too high? ________________________________________________
______________________________________________________________________________
8. In an imaginary world, far, far away, live some very strange creatures called sporks. Sporks
have two very unique recessive traits. Sporks who are homozygous recessive for the F/f allele
breathe fire. Sporks who are homozygous recessive for the G/g allele have very bad gas. Once in
a while a baby snork is born that takes its first breath and immediately combusts (due to the bad
combination of fire and gas).
a. Write the genotype for a spork who can breathe fire and has bad gas. ___________
b. Write the genotype for a spork who can breath fire and it homozygous for not having bad gas.
______________
c. Write the genotype for a spork who is heterozygous for both alleles. ____________
 A male spork is heterozygous for both traits. His mate, a female spork, is heterozygous for the
gas trait and homozygous recessive for the fire breathing.
a. What is the male spork’s genotype? ______________
b. What are the possible alleles that the male spork could pass along?
c. What is the female spork’s genotype? ___________
d. What are the possible alleles that the female spork could pass along?
e. Draw the dihybrid Punnett square for this cross.
f. What are all the genotype probabilities for this cross? _____________________
g. What are all the phenotype probabilities for this cross? ____________________
h. What is the chance that a baby of this cross would spontaneously combust at birth (ie be gassy and
fire breathing) ____________________________________