homework#7 (tut 15-16)

Question 1

Part complete

In humans, what determines the sex of offspring and why?

Answer 1

The male gamete determines sex because each male gamete can contribute either an X or a Y chromosome.

Question 2

SRY is best described in which of the following ways?

Answer 2

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

Question 3

Duchenne muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human X chromosome. The patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein. They rarely live past their 20s. How likely is it for a woman to have this condition?

Answer 3

Very rarely: it is rare that an affected male would mate with a carrier female.

Question 4

All female mammals have one active X chromosome per cell instead of two. What causes this?

Answer 4

activation of the XIST gene on the X chromosome that will become the Barr body

Question 5

In general, the frequency with which crossing over occurs between two linked genes depends on what?

Answer 5

how far apart they are on the chromosome

Question 6

What is the reason that closely linked genes are typically inherited together?

Answer 6

They are located close together on the same chromosome.

Question 7

In Drosophila, two genes on the fourth chromosome, bent wings (b) and shaven bristles (s) are completely linked. If a fly with the genotype bbss is crossed to a fly with the genotype BbSs, what type(s) of gametes will their offspring produce.

Answer 7

BS and bs