Chapter 2.5: Overview of Sex Chromosomes and X/Y Linked Traits

primordial gonad

structure that eventually becomes ovaries or testes

cortex

potential to be an ovary

medulla

potential to be a testis

Sry gene

gene that determines sex

Sry protein

the Sry gene triggers the synthesis of the…

ovary

if no sry protein, the cortex becomes an _____

wolffian system and mullerian system

both sexes begin with two sets of reproductive ducts…

wolffian system

reproductive duct that develops into the male reproductive system: seminal vesicles, vas deferens

mullerian system

reproductive duct that develops into the female reproductive system: uterus, vagina, fallopian tubes

third (3rd) prenatal month

when does the differentiation of ducts happen?

testosterone and mullerian inhibiting substance; the wollfian system to develop, mullerian degenerate, & testes descend

if a testes has been created, they will produce… causing…

no testicular hormones; mullerian system to develop and wolffian degenerate

if there are no testes… causing …

bipotential precursor

external reproductive structures (genitalia) develop from one _______

2nd month

when does differentiation of the external reproductive organs occur?

testosterone

what determines whether the external reproductive organs become male or female?

puberty

when is fertility achieved?

puberty

when do the secondary sex characteristics develop?

secondary sex characteristics

features unrelated to reproduction that distinguish sexually mature men and women

GH, Gonadotropic hormone (FSH, LH), adrenocorticotropic hormone (ACTH)

puberty increases the release of anterior pituitary hormones such as…

growth hormone

this hormone acts on bone and muscles

gonadotropic hormone

this hormone helps with the growth of the gonads

androgens and estrogens

relative levels of _____ & ______ determine whether male or female features develop in puberty

androstenedione

an androgen that is necessary for the growth of axillary and pubic hair in females

female

this sex’s brain has stronger side to side connections and is optimized for intuitive thinking

male

this sex’s brain has stronger front to back connections and is optimized for motor skills

True

True or False: whether you are male or female can determine how various diseases/disorders effect you as the brains are structured somewhat differently. 

Pfeiffer; 1936

who first discovered a sex difference in mammalian brain function? What year?

neonatal rats

what did Pfeiffer use for his gonad research?

male

pfeiffer found that perinatal androgens lead to ___ pattern

estradiol

evidence suggests that ____ masculinizes the brain, at least in rodents

cholesterol

sex steroids are all derived from _______ and are readily converted from one to the other

• neonatal injections of estradiol masculinize

• dihydrotesterone can’t be converted to estradiol and doesn’t masculinize

• preventing testosterone from converting to estradiol interferes with its masculinizing effects

Why do we think estradiol causes masculinization of the brain?

Alpha fetoprotein in the blood during the perinatal period binds to circulating estradiol to prevent it from entering the brain

how does estradiol not masculinize female brains?

no single mechanism can account for the development of sexual dimorphisms of mammalian brains

what is the modern perspective on sexual differentiation of the mammalian brain?

True

True or False: female brain development may not automatically occur in absence of estrogens

masculinize

promoting male behavior

defeminize

preventing female behavior

masculinizes and defeminizes

perinatal testosterone in rats…

feminizes and demasculinizes

neonatal castration of male rats does what?

endocrine disruptors

will mimmic or mask the way that hormones affect gene transcription; can prevent genes from being transcribed

X chromosome

which chromosome is bigger? X or Y?

X chromosome

X vs. Y chromosome…which one is this?

is a sex chromosome that occurs paired in the female and single in the male

X chromosome

X vs. Y chromosome…which one is this?

contains genes for female sex determination

x chromosome

X vs. Y chromosome…which one is this?

has about 155 million base pairs

x chromosome

X vs. Y chromosome…which one is this?

represents 5% of the entire human genome

x chromosome

X vs. Y chromosome…which one is this?

contains more genes (about 1000)

y chromosome

X vs. Y chromosome…which one is this?

a sex chromosome which is normally present only in male cells

y chromosome

X vs. Y chromosome…which one is this?

contain genes for male sex determination

y chromosome

X vs. Y chromosome…which one is this?

has about 59 million base pairs)

y chromosome

X vs. Y chromosome…which one is this?

represents 2% of the entire human genome

y chromosome

X vs. Y chromosome…which one is this?

contains fewer genes (about 70)

y chromosome

X vs. Y chromosome…which one is this?

contains the SYR gene, which is involved in the development of the testes

males

are the heterogametic sex

females

are the homogametic sex

False; it is the opposite in birds and snakes

True or False: which sex is heterogametic vs homogametic is the same in all species

at the tip and bottom of both chromosomes

where are the shared psuedoautosomal regions?

pseudo autosomal regions

regions that have similar genes between the X and Y chromosome

center of the chromosome

where are they x and y linked genes on the chromome?

PAR1

which is bigger…PAR1 or PAR2?

~50% ratio

what is the ratio for male to female on a punnet square?

y-linked

traits or genes that are specific to the Y chromosome

less genes on the Y chromosome

why are y-linked traits less common?

1923

when was the y chromosome first seen?

psuedoautosomal regions (PAR1 and PAR2)

which part of the sex chromosomes cross over?

non-recombinant region

region of the chromosome that has all the Y (or X) linked traits

5%

the PAR regions make up about __% of the chromosome

63

how many pseudoautosomal genes are there that can cross over with the X chromosome?

False

True or False: Y linked traits can affect females

MSY

male specific region of Y chromosome

True

True or False: all sons of an affected father are affected by a Y-linked trait

SRY gene

gene on the y-chromosome that determines maleness

6 weeks

it is male sex switch which triggers developmental process toward maleness after __________ (amount of time) pregnancy

short stature & infertility issues

what were two traits passed on by the Y chromosome that he mentioned out loud in the lecture?

hemizygous wild type male

what does X⁺Y mean in relation to x-linked traits?

hemizygous mutant male

what does X^mY mean in relation to x-linked traits?

homozygous wild type female

what does X⁺X⁺ mean in relation to x-linked traits?

heterozygous female carrier

what does X⁺X^m mean in relation to x-linked traits?

homoxygious mutant female

what does X^mX^m mean in relation to x-linked traits?

males

most individuals who are affected with the trait or condition in question with x-linked traits are _____ (sex)

two; one

the basis for X-linked inheritance is that females have ___ X chromosomes and males have only ___ X chromosome

carriers; carriers or no gene

mothers of the affected males are ____ and the sisters of affected males are _____ (x-linked traits)

True

True or False: x-linked recessive traits are always expressed by hemizygous males

yes; no

will homozygote females show a recessive x-linked trait? will heterozygote females?

affected or heterozygous mother

who do affected males get an x-linked recessive trait from?

affected fathers and affected or heterozygous mothers

who do affected females get an x-linked recessive trait from?

x-linked recessive trait

is hemophilia recessive or dominant? x or y linked?

hemophilia

inability to clot blood (disorder)

A and B

two types of Hemophilia

unaffected son, carrier son, carrier daughter, unaffected daughter

a father without hemophilia and a carrier mother would result in what phenotypes? (2 males 2 female)

2 unaffected sons and 2 carrier daughters

a father with hemophilia and a mother who is not a carrier would result in what phenotypes (2 males 2 females)

x-linked recessive disorder

is color blindness X or Y linked? recessive or dominant?

ok

information about red-green color vision deficiency…I don’t think he’s gonna ask about this but just in case..

the visible spectrum is divided into two parts; a red segment and a blue segment, separated by grey or indistinct areas. The amount of grey or indistinct areas varies according to the severity of the deficiency. (if using writing mode just type ok).

men

what sex is mostly affected by color blindness?

color blind; carrier

for a women to be color deficient, her father must be ______ and her monther must be _____

carrier mother

a color blind male always inherits it from his ______ (specify whether usually carrier or affected)

duchenne muscular dystrophy

involves the wasting away of the muscle tissue; muscle cells become engorged with fat and they eventually waste away; most individuals suffer from respiratory failure in their early 20s.

x linked recessive disorder

is duchenne muscular dystrophy x or y linked? dominant or recessive?

50%

in duchenne msucular dystrophy inheritance, the son of a carrier mother has a __% chance of inheriting the defective gene from his mother

50%

in duchenne msucular dystrophy inheritance, the daughter of a carrier mother has a __% chance of being a carrier OR having two normal copies of the gene

one

x linked dominant traits are expressed with ___ copy