Chapter 10

Sickle-cell anemia is an inherited chronic blood disease caused by an autosomal recessive allele. Suppose a man who is homozygous recessive for the sickle-cell gene fathers a child by a woman who is a carrier for sickle-cell. What are the chances their children will exhibit the disease? (Note: A Punnett square may be useful.)

50%

All humans are capable of producing gametes containing different sex chromosomes.

False

Males with a recessive X-linked allele that causes a disorder do not always show symptoms because they can also carry a dominant allele on their Y chromosome.

False

Which of the following statements about crossing-over is true?

It disrupts the linkage between genes.

Sex-linked genes are found on either the X chromosome or the Y chromosome but not both.

True

Down syndrome in humans is an example of

a change in the overall number of chromosomes.

Which of the following genetic changes would not be heritable?

a mutation in a skin cell

Most inherited human disorders are the result of

recessive mutations of genes located on autosomes.

The probability that two genes will be separated by crossing-over is related to:

the distance between the two genes on the chromosome.

On chromosomes, a pair of linked genes will be found only on

the same chromosome