Chapter 15 q &a

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1

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?

tortoiseshell females; black males

2

Calico cats are female because

a male inherits only one of the two X-linked genes controlling hair color.

3

Women (and all female mammals) have one active X chromosome per cell instead of two. What causes this?

modification of the XIST gene so that it is active only on one X chromosome, which then becomes inactive

4

Which of the following statements is true of linkage?

The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.

5

What does a frequency of recombination of 50% indicate?

The two genes are likely to be located on different chromosomes.

6

What is the reason that linked genes are inherited together?

They are located close together on the same chromosome.

7

Recombination between linked genes comes about for what reason?

Crossovers between these genes result in chromosomal exchange.

8

Why does recombination between linked genes continue to occur?

New allele combinations are acted upon by natural selection.

9

If nondisjunction occurs in meiosis II during gametogenesis, what will be the result at the completion of meiosis?

1/4 of the gametes will be n + 1, 1/4 will be n - 1, and 1/2 will be n.

10

Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?

47, +21

11

What is the source of the extra chromosome 21

nondisjunction or translocation in either parent

12

At which phase(s) is it preferable to obtain chromosomes to prepare a karyotype

late prophase or metaphase

13

Which of the following produces a Mendelian pattern of inheritance?

a trait acted upon by many genes