Ch 4 Sex-Determination and Sex-Linked Characteristics

Question 1

Describe the XX-XY Sex Determination System

Answer 1

female cells have two x chromosomes, while males have one x and one y chromosome

Question 2

how can X and Y chromosomes pair up in meiosis?

Answer 2

X and Y chromosomes contain pseudoautosomal regions, which are small regions of the chromosome that are homologous to each other

Question 3

is sex determined by individual genes or by the sex chromosomes?

Answer 3

sex is determined by individual genes

Question 4

what does an X:A ratio of 1.0 produce?

Answer 4

female

Question 5

what does an X:A ratio of 0.5 produce?

Answer 5

male

Question 5

what does an X:A ratio between 0.5 and 1.0 produce?

Answer 5

intersex

Question 6

what does an X:A ratio less than 0.5 or greater than 1.0 produce?

Answer 6

metamale or metafemale

Question 7

what is Turner syndrome? what are some characteristics of it?

Answer 7

XO; females only have one X chromosome
sterile, short, underdeveloped sex characteristics

Question 8

what is Klinefelter syndrome? what are some characteristics of it?

Answer 8

multiple X chromosomes in male (XXY)
small testes, reduced facial/pubic hair, taller, sterile

Question 9

what is Triple-X syndrome and what are some characteristics of it?

Answer 9

females with XXX; tend to be tall and thin and slight intellectual disability

Question 10

what is XYY syndrome and what are some characteristics of it?

Answer 10

males with extra Y chromosome; no distinctive physical characteristics besides being taller and some learning disabilities

Question 11

what determines maleness in humans?

Answer 11

SRY gene on the Y chromosome

Question 12

what is the phenotype if the SRY gene is absent?

Answer 12

female phenotype

Question 13

describe androgen-insensitivity syndrome?

Answer 13

prevents testosterone from binding to androgen receptors, therefore resulting in female characteristics, despite SRY gene being present
however testes are still present and female fails to menstruate due to sexual organs being absent

Question 14

what are the 5 inferences about the roles of sex chromosomes?

Answer 14

1. X chromosome contains genetic information for both sexes, therefore at least one X chromosome is required for human development
2. Presence of SRY gene determines maleness
3. Absence of Y chromosome usually results in female phenotype
4. Fertility genes located on both X and Y chromosomes; at least 2 X chromosomes needed to be fertile
5. More than 2 X chromosomes results in abnormal development

Question 15

traits determined by genes located on sex chromosomes

Answer 15

sex-linked characteristics

Question 16

traits determined by genes on X chromosomes

Answer 16

X-linked characteristics

Question 17

traits determined by genes on Y chromosomes

Answer 17

Y-linked characteristics

Question 18

phenomenon when two chromosomes fail to separate in anaphase I of meiosis

Answer 18

nondisjunction

Question 19

what would occur from a nondisjunction of two X chromosomes

Answer 19

one gamete has two x chromosomes, while the other has none; when fertilized, the zygote with no x chromosomes will die

Question 20

mechanisms that equalize the amounts of protein produced

Answer 20

dosage compensation

Question 21

how is dosage compensation demonstrated in sex chromosomes

Answer 21

only one X chromosome is expressed; other X chromosomes are inactivated into Barr bodies

Question 22

what are Barr bodies

Answer 22

inactive X chromosomes

Question 23

how can females be mosaic for X-linked traits

Answer 23

due to females forming Barr bodies, half of the cells may express one allele from one X chromosome, while the other half of the cells may express the allele from the other X chromosome

Question 24

how can females be mosaic for X-linked traits

Answer 24

due to females forming Barr bodies, half of the cells may express one allele from one X chromosome, while the other half of the cells may express the allele from the other X chromosome