Chapter 4

Question 1

sex chromosomes

Answer 1

a type of chromosome involved in sex determination

Question 2

autosomes

Answer 2

one of the numbered chromosomes, as opposed the sex chromosomes

Question 3

psuedoautosomal regions

Answer 3

small region of the X and Y chromosomes that contain homologous gene sequences

Question 4

lyon hypothesis

Answer 4

proposal by Mary Lyon in 1961 that one X chromosome in each female cell becomes inactivated (a Barr body) and that which of the X chromosomes is inactivated is random and varies from cell to cell

Question 5

Barr body

Answer 5

inactivated X chromosome that appears as a condensed, darkly staining structure in most cells of female placental mammals

Question 6

Turner syndrome

Answer 6

A chromosomal disorder in which a female is born with only one X chromosome

Question 7

klinefelter

Answer 7

a genetic condition in which a male is born with an extra copy of the X chromosome (isn’t inherited but occurs as a result of random genetic error)

Question 8

drosphilia sex determination

Answer 8

achieved by a balance of female determinants on the X chromosomes and male determinants on the autosomes

Question 9

hemizygous

Answer 9

a term that describes a person who has only one copy of a gene rather than the usual two copies

Question 10

reciprocal crosses

Answer 10

a concept of crossing a pair of parents with the sexes reversed

Question 11

non-disjunction

Answer 11

failure of homologous chromosomes or sister chromatids to separate in meiosis or mitosis – usually resulting in an abnormal distribution of chromosomes in the daughter nuclei

Question 12

x-chromosome inactivation (XCl)

Answer 12

is the form of dosage compensation in mammalian female cells to balance x-linked gene expression levels of the two sexes