Biology
Lacks
Name___________________________________
Period ____________
Genetics In-Class Worksheet #3
Pedigree for family with Albinism
1. Albinism is an autosomal (not sex-linked) recessive genetic disorder that results in the lack of
melanin pigment in the body. The pedigree below follows a family that has been affected by this
disorder. Refer to the legend below to remind you of the symbols used in a pedigree.
On the line below each person in the family, write their genotype. If the genotype cannot be
determined, write all possible genotypes. For this trait, use M to represent normal melanin pigment,
and m to represent albinism (lack of melanin). If there are any individuals who are certain to be
carriers, shade in half of their circle or square to represent this.
2. Create your own pedigree showing a man and a woman who have 3 children. The man and the
woman are both carriers for albinism. One of their children is a male carrier, one is a male who has
albinism and one is a female who is totally normal. Write genotypes below all shapes.
On all problems below, SHOW YOUR WORK. Show all crosses, using Punnett Squares. Use P to
designate your parents (or P1 and P2 for 2 generations of parents), F1 for your first generation of
offspring, and F2 if you have a second generation of offspring. Report all of the expected phenotypes
of offspring using fractions, ratios or percents.
Sex Linkage
3. In humans, red-green color blindness is an x-linked recessive trait; the normal condition is
dominant. A woman who is homozygous normal marries a man who is color blind. What is the
probability that they would have a child who is normal? Explain using a Punnett Square. Use XR to
represent normal red-green vision, and Xr to represent color blindness.
4. In fruit flies, white eyes is an x-linked recessive trait (red eyes is dominant). Show the expected
offspring from crossing a red-eyed male fly with a white-eyed female fly. Use XR and Xr as your
alleles.
Blood Type (Codominance and Multiple Alleles)
5. Betty is heterozygous and has type A blood, and Bob is heterozygous and has type B blood. Use a
Punnett Square to show the likelihood that their first child will get each of the 4 blood types (A, B, AB,
O). Remember, the alleles for blood type are IA, IB, and i.
6. Mary has the blood type O. As an adult she finds out her parents both have the blood type AB.
What does this tell Mary about herself? Explain using a Punnett Square. Remember, the alleles for
blood type are IA, IB, and i.
Worksheet #3: CHALLENGE (Optional, for extra credit) – Choose 2 of these problems to do for
extra credit points, or if you’re bored, do them all just for practice!
Mystery Pedigree
1. Examine the pedigree chart below. This chart shows the inheritance of a certain disorder.
Individuals affected by this disorder are shown shaded in black.
Determine which of these patterns of inheritance are followed by this disorder, and circle the correct
one.
autosomal recessive
autosomal dominant
sex-linked recessive
sex-linked dominant
Trial and error is the best way to figure this out. Once you think you have determined the appropriate
pattern, fill in the blanks with the possible genotypes for each individual. Use the letters A and a to
represent the alleles for this trait. (or Xa and XA if it’s sex-linked)
Sex Linkage
2. In fruit flies, remember that white eyes is an x-linked recessive trait (red eyes is dominant). If the
offspring of a cross between 2 flies results in 25% red-eyed females, 25% white-eyed females, 25%
red-eyed males, and 25% white-eyed males, what would the genotypes of the parents be? Show with a
Punnett Square.
3. In addition to the white-eyed trait from above, there is also an autosomal recessive disorder called
Eyeless, which results in baby fruitflies being born with no eyes at all. What will be the distribution of
offspring if you follow a dihybrid cross between a white-eyed male fly that is heterozygous for the
eyeless trait with a homozygous red-eyed female fly that is eyeless? (Remember, if a fly is eyeless, it
doesn’t matter what color their eyes are!)
A trait that affects the expression of another trait is called epistatic. Which trait in the above problem
is epistatic? Explain your answer.
Blood Type
4. John and Jill have 6 children together. Half of their children have the blood type A, and half have
the blood type B. What are the genotypes of the parents? Explain using a Punnett Square.
5. Remember that in humans the gene for hanging earlobes is dominant over the gene for attached
earlobes. Follow a dihybrid cross between a parent who has type AB blood and attached earlobes
with a parent who has type AB blood and is heterozygous for hanging earlobes.