Topic 4: Sex Linkage and Pedigrees

Question 1

females are _______

Answer 1

homogametic

Question 2

males are ______

Answer 2

heterogametic

Question 3

_______ are in most of our chromosomes

Answer 3

autosomes

Question 4

______ chromosomes are differently represented in sexes

Answer 4

sex

Question 5

wildtype (most common phenotype of a population) is denoted with a _____

Answer 5

+

Question 6

males and females have different phenotypic ratios in F1/F2
reciprocal crosses give different results
“criss-cross inheritance”

these are all indicators of…

Answer 6

sex-linked inheritance

Question 7

Thomas Hunt Morgan studied…

Answer 7

drosophila flies (fruit flies!)

Question 8

______: transmission of recessive allele on the X chromosome

Answer 8

X-linked recessive

Question 9

______: transmission of dominant allele on the X chromosome

Answer 9

X-linked dominant

Question 10

______: transmission of recessive allele on autosomes (ex: aa)

Answer 10

autosomal recessive

Question 11

______: transmission of dominant allele on autosomes (ex: AA, Aa)

Answer 11

autosomal dominant

Question 12

______-______ traits: alleles are carried in both sexes but the phenotype only shows up in one sex

Answer 12

sex-limited

Question 13

______-______ traits: inheritance patterns vary between the sexes even if the genotype is the same, usually influenced by hormone levels

Answer 13

sex-influenced

Question 14

how does sex determination work in drosophila flies?

Answer 14

X:A (X:autosome) ratio

Question 15

if X/A = 1, _______
if X/A <0.5, _________
if X/A 0.5-1, __________

Answer 15

1. female
2. male
3. intersex

Question 16

sex determination in mammals depends on…

Answer 16

presence of Y chromosome

Question 17

sex determination in birds, some reptiles, certain fish, moths, and butterflies uses the ______ system

Answer 17

Z/W system

Question 18

in the Z/W sex determination system, how are females defined?

Answer 18

ZW, heterogametic and hemizygous

Question 19

in the Z/W sex determination system, how are males defined?

Answer 19

ZZ, homogametic

Question 20

in the Z/W sex determination system, does Z or does W behave like X-linked genes in mammals?

Answer 20

Z-linked genes behave like X-linked genes

Question 21

W-linked genes are _____ (only occur in females)

Answer 21

matrilineal

Question 22

in roundworms and nematodes, they use X:A ratio to determine sex, a roundworm with the genotype XX would be _________

Answer 22

hermaphrodite, usually self-fertilizes

Question 23

in roundworms and nematodes, they use X:A ratio to determine sex, a roundworm with the genotype X0 would behave as _________

Answer 23

male, and produce “super-sperm” that can outcompete sperm from hermaphrodites, which increases genetic variation!

Question 24

true/false: you can’t have multiple sets of sex chromosomes involved in sex determination

Answer 24

false, platypus have 5 pairs of sex chromosomes! (X1Y1X2Y2X3Y3X4Y4X5Y5 = male)

Question 25

true/false: some reptiles and certain fish depend on environmental factors for sex determination

Answer 25

true! clownfish change sex depending on the temperature of water they’re in!

Question 26

_____________ balance the expression of X-linked genes

Answer 26

dosage compensation mechanisms

Question 27

______: one X chromosome is randomly inactivated in each female somatic cell

Answer 27

X-inactivation

Question 28

an inactivated X-chromosome in females becomes…

Answer 28

a Barr body (localized to a specific region of the wall of the nuclear envelope)

Question 29

Since X-inactivation is random… 1/2 somatic cells inactivate ______ and 1/2 somatic cells inactivate

Answer 29

1. maternal chromosome/alleles
2. paternal chromosome/alleles

Question 30

since mom and dad’s chromosomes may not be the same in X-inactivation, the daughter is heterozygous! which consequently results in…

Answer 30

a mosaic of 2 kinds of cells (we get individual cell phenotypic expression!)

Question 31

what’s an example of X-inactivation that results in a mosaic?

Answer 31

female calico cats!