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Problem 1
 In garden peas, an allele T for axial flowers (positioned along the stem) is dominant to
an allele t for terminal flowers (positioned at the tips of the branches).
a) In the F2, generation of a monohybrid cross, what is the expected ratio of
axial: terminal?
b) Among the F2, progeny, what proportion are heterozygous?
c) Among the F2 progeny with axial flowers, what proportion are heterozygous?
d) In a test cross of the F1, progeny of a monohybrid cross, what is the
expected ratio of axial : terminal?
Problem 2
 Complete the chart below
by placing a 0, 1/4, 1/2, or 1
in each box, corresponding
to the proportion of each
genotype ofoffspring
expected from each type of
mating
Problem 3
 A round pea seed is germinated and the mature plant self-fertilized. It produces some
wrinkled seeds. What was the genotype of the original seed? What is the expected
proportion of wrinkled seeds produced by the mature plant?
Problem 4
 The recurrence risk of a genetic disorder is the probability that the next child born into
a sibship will be affected, given that one or more previous children is affected. What
isthe recurrence risk for:
– a) A dominant trait in which one parent is affected?
b) A recessive trait in which neither parent is affected?
– c) A recessive trait in which one parent is affected?
Problem 5
With independent assortment, how many different types of gametes are possible from the
genotype Aa Bb Cc, and in what proportions are they expected?
Problem 6
 The pedigree shows individual II-2 affected with a recessive trait. Let A and a
represent the dominant and recessive alleles

– a) What is the genotype of II-2 ?
– b) What are the genotypes of I-1 and
I-2?
– c) What are the possible genotypes of
II-1 and II-3?
– d) What is the probability that II-3 is a
heterozygous "carrier" of the a allele?
Problem 7
 Huntinhton disease is a rare degenerative human disease determined by a dominant
allele, HD. The disorder is usually manifested after the age of 45. A young man has
learned that his father has developed the disease.
– a) What is the probability that the young man will later develop the disorder?
– b) What is the probability that a child of the young man carries the HD allele?
Problem 8
 Assume that the trait in the accompanying pedigree is due to simple Mendelian
inheritance.
– a) Is it likely to be due to a dominant allele or a recessive allele? Explain.
– b) What is the the meaning of the double horizontal line connecting III-1 with
III-2?
– c) What is the biological relationship between III-1 and III-2?
– d) If the allele responsible for the condition is rare, what are the most likely
genotypes of all of the persons in the pedigree in generations I, II, III?
Problem 9
 A recessive mutation of an X-linked gene in human beings results in hemophilia,
marked by a prolonged increase in the time needed for blood clotting. Suppose that a
phenotypically normal couple produces two normal daughters and a son affected with
hemophilia.
– a) What is the probability that both of the daughters are heterozygous carriers?
– b) If one of the daughters and a normal man produce a son, what is the
probability that the son will be affected?
Problem 10
 Duchenne-type muscular dystrophy is an inherited disease of muscle due to a mutant
form of a protein called dystrophin. The pattern of inheritance of the disease has these
characteristics: (1) affected males have unaffected children,
(2) the unaffected sisters of affected males often have affected sons,
(3) the unaffected brothers of affected males have unaffected children.
What type of inheritance do these findings suggest? Explain your reasoning