3.3 - 3.6

Question 1

Sex-linked inheritance

Answer 1

refers to the hereditary transmission of genes on the sex chromosomes

Question 2

X-linked inheritance

Answer 2

a term identifying the transmission of genes carried on the X chromosome.
(mode of transmission of eye color in Drosophila)

Question 3

hemizygous

Answer 3

a term meaning “half-zygous”, for X-linked genes. Term is used because males have a single X chromosome; therefore, unlike femailes, males cannot be homozygous or heterozygous for X-linked genes. because they have no corresponding gene on their Y chromosome.

Hemizygous males inherit their X chromosome from their mother; moreover, they express any allele on thier X chromosome, since the Y chromosome does not carry genes that are homologous to those on the X chromosome.

Question 4

Sex determination

Answer 4

encompasses the genetic and biological processes that produce the male and female characteristics of a species.

Question 5

X/A ratio

X/autosome ratio

Answer 5

the ratio of X chromosomes to the number of haploid sets of autosomes

Question 6

Z/W system

Answer 6

in many bird species, some reptiles, certain fish, and moths and butterflies, females carry two different sex chromosomes, and males carry two sex chromosomes that are the same. the Z/W system is used to describe the chromosomes of these species to avoid confusion for the XX/XY system

males have two Z sex chromosomes (ZZ)

females have a Z and a W chromosome (ZW)

Question 7

pseudoautosomal region (PAR)

Answer 7

a region on human X and Y chromosomes that have a few genes in common. “regions of homology”.

allows X and Y chromosomes to pair as homologs during meiosis

regions are called PAR1 and PAR2

their pattern of inheritence resembles autosomal transmission making them “pseudoautosomal”

crossing over undergoes there during meiosis between X and Y chromosomes

Question 8

dosage compensation

Answer 8

any mechanism that compensates for differences in the number of copies of genes due to the different chromosome constitutions of males and females is called dosage compensation.

at least three mechanisms that equalize X-linked gene expression between male and female animals.

Question 9

random X inactivation

Answer 9

in approximately half the somatic cells in a female embryo, the maternally dervived X chromosome is inactivated. In the other half, the paternally derived X chromosome is inactivated. This is a mechanism for dosage compensation.

Question 10

Barr body

Answer 10

an inactivated X chromosome