First Check #7 (tut 15-16)

Question 1

If a male affected by a recessive sex-linked trait reproduces with a female who is homozygous wild type for that trait, what is the chance that any of their offspring will have the trait?

Answer 1

0

Question 2

Pull out a piece of paper and pencil because this question will take some thought. First, work out the predicted offspring of a mating between a white-eyed female and a red-eyed male Drosophila. Next, work out the predicted offspring of a heterozygous red-eyed female and a white-eyed male. What is the result of both crosses?

Answer 2

In the first case, all females will have red eyes and all males will have white eyes. In the second case, there will be equal numbers of white and red eyes.

Question 3

You are working for a fly geneticist who sends you to a produce market to find new mutations. You rummage through the dumpsters and capture 100 flies. You note that 100% of the flies have red eyes and 90% have long body bristles (10% have short body bristles). Based on these results, you can conclude that __________________

Answer 3

in this produce market, red eyes and long bristles are wild-type traits

Question 4

Males are more often affected by sex-linked traits than females because

Answer 4

males are hemizygous for the X chromosome

Question 5

SRY is best described as

Answer 5

a gene region present on the Y chromosome that triggers male development

Question 6

In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?

Answer 6

tortoiseshell females; black males

Question 7

Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?

Answer 7

XNXn and XNY

Question 8

Of the following statements, which is/are usually true if the genes for two different characters are linked?

Answer 8

The genes are on the same chromosome and do not assort independently.

Question 9

When genes on a particular chromosome do not assort independently in genetic crosses, the genes are _______________.

Answer 9

linked

Question 10

What ratio of F1 generation phenotypes would be expected from a test cross of flies differing in two characters (females are heterozygous for both genes, and males are homozygous recessive for both genes) if the two genes assort independently of each other?

Answer 10

1:1:1:1

Question 11

You are studying two genes that are located on the same chromosome. They are located 55 map units apart. How will the alleles of these genes behave in a dihybrid cross?

Answer 11

They will appear to segregate independently, as if they are located on different chromosomes.

Question 12

How do the events of meiosis I promote the production of new combinations of alleles?

Answer 12

via both crossing over between homologous chromosomes and independent assortment

Question 13

If the recombination frequency between P and O is 7.4, and between N and O it is 7.9, what is the likely order of these genes on the chromosome if the distance between N and P is 15.7?

Answer 13

Either P-O-N or N-O-P

Question 14

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel’s law of independent assortment?

Answer 14

The arrangement of each pair of homologous chromosomes on the metaphase plate during metaphase I is random with respect to the arrangements of other pairs.

Question 15

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel’s law of segregation?

Answer 15

The two alleles for each gene separate as homologous chromosomes move apart during anaphase I.