Ch 4: Sex Determination and Sex Related Traits (Bio 375 - Genetics)

Question 1

sex chromosome

Answer 1

chromosome involved in sex determination; X and Y chromosomes in humans

Question 2

autosomal chromosome (autosome)

Answer 2

chromosome which is not a sex chromosome

Question 3

sex determination by sex chromosomes: XX-XY

Answer 3

for humans – XY = males = heterogametic sex, XX = females = homogametic sex

Question 4

heterogametic sex

Answer 4

two different sex chromosomes

Question 5

homogametic sex

Answer 5

two identical sex chromosomes

Question 6

sex determination by sex chromosomes: ZZ-ZW

Answer 6

for birds – ZZ = male = homogametic, ZW = females = heterogametic

Question 7

sex determination by sex chromosomes: XX-XO

Answer 7

for grasshoppers, no “male” chromosome… the O represents a lacking sex chromosome

Question 8

crossing over involves

Answer 8

the exchange of similar genetic material in equal amounts

Question 9

primary/secondary pseudoautosomal regions on sex chromosomes

Answer 9

where crossing over can occur during spermatogenesis

Question 10

hermaphroditism

Answer 10

both sexes are present in same organism

Question 11

monoecious

Answer 11

organisms with both male and female reproductive structures

Question 12

dioecious

Answer 12

organism has either male or female reproductive structures; sex may be determined chromosomally/genetically/environmentally

Question 13

X chromosome

Answer 13

at least one copy required for human development; abnormal copies beyond normal number result in developmental disorders

Question 14

Y chromosome

Answer 14

single copy of this chromosome is all that is required for male development due to SRY gene

Question 15

SRY gene

Answer 15

gene causes gonads to develop into testes which secrete: testosterone (inducing development of male characteristics) and mullerian inhibiting substance (degenerates female reproductive ducts)

Question 16

turner syndrome

Answer 16

XO; only a single X chromosome; sterile female with underdeveloped secondary sex characteristics

Question 17

klinefelter syndrome

Answer 17

XXY; feminized male phenotype; multiple X chromosomes and/or 1+ Y chromosomes

Question 18

dosage compensation

Answer 18

equalizes amount of protein produced by X-linked genes in two sexes; one X chromosome is inactivated in female cells to become a Barr body; this results in only one active X chromosome in each cell, or one “dose” of X-linked genes

Question 19

lyon hypothesis

Answer 19

during early development one X chromosome is inactivated in each cell during dosage compensation -> X to inactivate is determined at random in each cell and the inactivation is permanent (inactivated X remains inactivated in all descendant cells)

Question 20

mosaics

Answer 20

an individual consisting of cells of more than one chromosomal composition; of differing genetic composition; expression of X-linked genes is different in different cells; some cells express maternal X and others express paternal X (heterozygotes, tortoiseshell cats)

Question 21

sex linked traits

Answer 21

determined by genes located on sex chromosomes; first described by Thomas Hunt Morgan (using fruit fly genetics and winning the nobel prize in 1933 for his work)

Question 22

hemizygous

Answer 22

males having only one single allele for X-linked loci

Question 23

+ symbol on a gene

Answer 23

wild type, not mutated

Question 24

reciprocal cross

Answer 24

used to determine if a trait is influenced by the sex of the parent/is sex linked

Question 25

sex limited traits

Answer 25

autosomal traits that are only expressed in one sex even though the genes are present in both sexes; tend to be hormonally regulated (ex: milk production, egg production, multiple ovulation/twinning allele)

Question 26

sex influenced traits

Answer 26

autosomal traits which are due to genes whose expression depends on hormonal background; exhibits a different expression pattern in different sexes – an allele may be dominant in one sex and recessive in another (ex: pattern baldness is dominant in males but recessive in females, longer index finger length is dominant in females but recessive in males)

Question 27

completely dominant allele

Answer 27

what is expressed phenotypically in heterozygotes