Additional problems for lectures 1, 2, and 3. Most of these are from past years exams. They will be representative of the kinds of problems that will appear on the Spring 2001 exams.

1) A plant heterozygous for four independently assorting pairs of genes (Aa, Bb, Cc, Dd) and homozygous for a fifth (EE) is crossed to a second plant heterozygous for all five genes (Aa, Bb, Cc, Dd, Ee).

a) Determine the expected frequency of the following genotypes in the progeny of such a plant:

i) aa bb cc dd EE

ii) aa bb Cc Dd Ee

iii) Aa Bb Cc Dd Ee

b) Determine the expected frequency of the parental phenotype among the progeny.


2) With which of the following modes of inheritance are the following pedigrees inconsistent: autosomal recessive, autosomal dominant, X-linked dominant, X-linked recessive? Provide a BRIEF justification for each answer.

Pedigree (a)


Pedigree (b)


Pedigree (c)


Pedigree (d)

3) Suppose you were on a jury to decide the following case: The Jones family claims that baby Jane, given to them at Chicago Hope, does not belong to them and that baby Sara, who was presented to the Smith family, really be longs to the Jones family. The Jones allege that the babies were exchanged soon after birth as part of "Sweeps Week" plot to improve ratings. The Smiths deny the allegation. Blood group determinations show the following results:

Ms. Jones, AB

Mr. Jones, O

Mrs. Smith, A

Mr. Smith, O

Baby Jane, A

Baby Sara, O

Which baby belongs to which family?



4) In sheep white fleece (W) is dominant over black fleece (w). Horned (H) is dominant over hornless (h) in males, but is recessive in females.

a) If a homozygous white horned male is bred to a homozygous hornless black ewe, what will the appearance of the F1? What about the F2?


b) A horned white ram was bred to the following four ewes with the following results:



Ewe A hornless, black

1 horned white female

Ewe B hornless, white

1 hornless black female

Ewe C horned, black

1 horned, white female

Ewe D hornless, white

1 hornless, black male + 1 Horned white female

What are the genotypes of the five parents?


5) In mammals X chromosome dosage compensation is achieved via the inactivation of one of the two Xs present in females. In eutherian mammals (mice, orangutans, undergraduates) the inactivation process is random: Individual cells inactivate eith er the paternally-derived or the maternally-derived X chromosome with equal probability. In contrast, in marsupials (opossums, kangaroos, Tasmanian devils) all cells inactivate the same X chromosome. Furthermore, the inactive X is always derived from the same parent.

(a) Given the following pedigree for an X-linked trait in kangaroos, can you determine whether it is the paternal X or the maternal X that is inactivated in marsupials? If so, state your reasons. If you cannot tell, explain why, and describe a s imple cross, or set of crosses, that will allow you to distinguish the possibilities.


(b) Based on your answer to part (a): What can you say about the phenotypes and genotypes of the grandparents? If there are ambiguities briefly explain why.


6) Mary and her brother Paul are both healthy adults. Mary and her live-in boyfriend Mike have a healthy baby girl and Mary is pregnant again. They learn that Mary and Paul's mother has just had a baby by a second marriage, and the baby has Duchenne muscular dystrophy. (DMD is a rare X-linked recessive disorder.)

a. Draw the pedigree of the individuals described and their relevant relatives.

b. Do Mary and Mike have to worry about their new baby having DMD? Explain.

c. If so, what is the probability the baby will have DMD?

d. Why didn't Mary and Paul and the first baby get DMD?



7) What is the MAXIMUM number of phenotypes that could result from the mating of F1 progeny from a cross of AA BB males and aa bb females (A and B are unlinked)? How could this come about?