Chap 6: Matters of Sex

Question 1

Sexual Development

Answer 1

All embryos develop unspecialized gonads and reproductive ducts during the 5th week of prenatal development.
Sex is based on the absence or presence of the Y chromosome, specifically the SRY gene which is the sea determine region of the Y chromosome.

Question 2

Sex Chromosomes Determine Gender

Answer 2

Human males are Heterogametic sex because they have an X and a Y chromosome.

Human females are homogametic because they have tow X chromosomes (XX).

Question 3

Probability of sex in humans

Answer 3

50/50 chance of female or male

             X           X

X XX XX

Y XY XY

Question 4

X chromosome

Answer 4

Contains more than 15,000 genes

Is larger than the Y chromosome

Question 5

Y chromosome

Answer 5

Contains 231 genes

2/3 is heterochromatin

Question 6

SRY gene

Answer 6

Encodes a transcription factor that controls the expression of the genes and stimulates male development.

Question 7

Anit-Mullerian

Answer 7

Secreted from the developing testes and destroys female structures.

Question 8

DHT (testosterone and dihydrotesterone)

Answer 8

Secreted to stimulate the development of male structures.

Question 9

Pseudohermaphroditism

Answer 9

Androgen insensitivity syndrome is the lack of androgen receptors and is chromosomal XY.

Male structures on the inside, looks like a girl on the outside.

Normal Y chromosome, wild type SRY gene.

Question 10

Y Linked Traits

Answer 10

Genes on the Y chromosome are Y-Linked
These traits are transmitted from male to male but are rear.

Females are not affected because they do have a Y chromosome.

Involve infertility and are not transmitted.

Question 11

X-Linked Traits in Males

Answer 11

Only one copy needed to show expression on a male because they only have one X chromosome.

Question 12

X-Linked Traits in Females

Answer 12

In female two copies are required for expression of recessive allele, one copy for dominant allele.

Passed from mother to son.

The affected female has an affected father and a mother who is affected or a heterozygote.

Question 13

X-Linked Dominant Inheritance in Females

Answer 13

Expressed in one copy.

High rates of miscarriage due to early lethality in males.

Question 14

X-Linked Dominant Inheritance in Males

Answer 14

More severe in males because he has no other allele to mask the affect.

Passed from male to daughters but no sons because a son’s X chromosome comes from his mother.

Question 15

X-Linked Recessive Trait

Answer 15

Affected males have a carrier mother.

Unaffected females with a carrier brother have a 50% chance of being a carrier.

An affected female has a carrier or affected mother AND an affected father.

A carrier female has a carrier mother or an affected father.

Question 16

X-Linked Dominant Traits

Answer 16

Rare.

There might not be any affected males because they die early.

An affected female has an affected mother.

Question 17

Sex Limited Traits

Answer 17

Traits which affect a structure or function occurring only in one sex.

Sex Linked or autosomal.

0% penetrance in one sex (usually female).
Example:
Beard growth a woman won’t have heavy beard growth but can pass those heavy growth genes to her sons.

Question 18

Sex- Influenced Traits

Answer 18

Autosomal traits in which the phenotype expressed by a heterozygote is influence by sex.

The allele is dominant in one sex but recessive in the other.

Example:
In pattern baldness is the heterozygous man is bald but the woman is not.

Question 19

Bar Body

Answer 19

X chromosome inactivation

Can alter the phenotype but not the genotype.

Question 20

Genomic imprinting

Answer 20

Male genome controls placenta development

Female genome controls embryo development

Prader Willi Syndrome: from father (chromosome 15 deletion)

Angelman Syndrome: from mother (chromosome 15 deletion)

Question 21

Genomic Imprinting

Answer 21

Methyl (CH3) groups cover a gene or several liked genes and prevent them from being accessed to synthesize protein.