homework page 2

2.01 Mendel's analysis of dihybrid crosses led to the principle of independent assortment, a very important idea related to the idea that genes act as particles.

(a) Using your own words, explain what is meant by independent assortment. You can look up the definition first in the textbook glossary, but be sure you can state what these terms mean in language that you understand.

(b) Why is it necessary to use a dihybrid cross to demonstrate independent assortment?

2.02 Two of the traits Mendel studied in peas were flower position and pod color. From monohybrid crosses, he determined that axial flowers (A) is dominant to terminal (a), and green pods (P) is dominant to yellow (p). Suppose that you pollinate the flowers of a plant with axial flowers and green pods with pollen taken from a plant with terminal flowers and yellow pods. Both of these parent plants are known to be true-breeding. F1 plants are then allowed to self pollinate to produce the F2 generation.

(a) What are the genotypes and phenotypes of the parents (P generation)?

(b) What genotypes and phenotypes are possible in the F1 plants?

(c) Using a Punnett square, determine which genotypes and phenotypes are possible in the F2 generation and calculate the expected ratio of each.

(d) Would you expect the results of this cross to be different if, in the P generation, the pollen had come from the axial/green plant and the terminal/yellow plant was used as the female? Explain.

2.03 A cross was made between fruit flies of genotypes AAbb and aaBB.

(a) Show the Punnett square for the expected F2 progeny types.

(b) What proportions of A-B-, A-bb, aaB-, and aabb progeny do you expect in the F2?

2.04 In a particular cross, one parent has genotype RrYy.

(a) What is the probability of this parent producing each of the following types of gametes: RY, Ry, rY, and ry?

(b) If the other parent has genotype rryy, what is the probability that an offspring will be RrYy? Rryy? RRYy?

2.05 Consider the following crosses in Drosophila. The two traits being investigated involve eye color and the presence or absence of wing crossveins. The outcomes of four crosses are shown below.

(a) Which eye color is dominant and which is recessive?

(b) Which wing vein type is dominant and which is recessive?

(c) What is the most likely genotype of each parent for each of the four crosses?

2.06 Consider the following cross: Aa Cc FF Yy Rr NN x AA CC Ff Yy Rr nn.

(a) List all possible different types of gametes the each parent can produce.

(b) What size (how many boxes) would the Punnett square have to be in order to analyze the progeny of this cross?

2.07 Some very complicated crosses are being done involving 32 different genes in mice. Calculate the total number of different gametes that could be produced by each of the following:

(a) How many different sperm could a male produce that is homozygous for all 32 genes?

(b) How many different eggs could a female produce that is heterozygous for 3 genes and homozygous for the other 29 genes?

(c) How many different eggs could a female produce that is heterozygous for 10 genes and homozygous for the other 22 genes?

(d) How many different sperm could a male produce that is heterozygous for all 32 genes?

2.08 There are two genes in fruit flies that determine eye color and wing shape. Red eyes is dominant to sepia (brown) eyes, and normal wings is dominant to vestigial (shriveled) wings. Describe a procedure you could use to determine the genotype of a fly that has red eyes and normal wings. This fly may be homozygous or heterozygous for either gene.