Genetics: Sex Determination

How does sex determination happen?

by specific genes

What is a homogametic sex?

Produces like chromosomes (XX)

What is heterogametic sex?

produces unlike chromosomes (XY)

What is phenotypic dimorphism?

visually determining sexual differentiation

-characteristics specific to each gender

What are autosomal chromosomes?

general body chromosomes

What is differentiation within embryogenesis?

the process where a group of unspecialized cells develop into a functional, recognizable group of cells that have a common function

Do embryos start out as hermaphroditic?

yes

What are the terms for the ducts of each sex?

Mullerian/ Paramesonephric= female

Wolffian/Mesonephric = male

What substance determines if a fetus is male?

SRY protein

-Without SRY/TDF, female reproductive tract forms

When will sexual differentiation be determined?

Around week 12 in fetal development

-during this time, oocytes are dormant in female fetus

What is the pseudoautosomal regions (PARs)?

Present on both ends of Y chromosome

Share homology with regions on X chromosome

Synapse and recombine with X during meiosis

What is the MSY?

Nonrecombining region of Y chromosome

What protein does SRY encode?

the Testis-determining factor (TDF)

What does TDF function as?

Functions as a transcription factor

-DNA binding proteins that stimulates its expression

What does SOX-9 do?

works to form the seminiferous tubules

What is the default sex?

female

What happens if DMRT1 is increased in birds?

has a “masculine” effect and decreases femininity

What is a gynandromorph chicken?

Rare, naturally occurring phenomena in which one side of the animal appears male and the other side female

What is a chimaera?

combination of two different cell lines creating one organism

What do Klinefelter and Turner syndrome result from?

nondisjunction: Failure of X chromosomes to segregate during meiosis

What are the characteristics of Klinefelter syndrome

-1/660 males

-They have male genitalia and internal ducts are rudimentary testes fail to produce sperm

-Feminine development not suppressed

Klinefelter syndrome can result in gynecomastia, what is that?

development of breasts

What are the characteristics of Turner syndrome

-1/2000 females

-Phenotypically female, but ovaries underdeveloped

-Cognitive impairment

What is the purpose of dosage compensation

Prevents excessive expression of X-linked genes in humans and other mammals by balancing doses of X chromosome expression

What are Barr bodies?

Highly condensed structure that lies against the nuclear envelope

Inactivated X chromosome

What is X-inactivation?

Explains dosage compensation

Follows N − 1 rule

Why does X-inactivation not affect Turner or Klinefelter syndrome?

Chromosome inactivation not in early stages of development for cells destined for gonadal tissue

-has 15% escape inactivation

What is the Lyon hypothesis?

-Inactivation of X chromosome is random

-Occurs in somatic cells at early stage of embryonic development

-All descendant cells have same X-inactivation

What is an example of the Lyon hypothesis?

Calico cats

What is temperature-dependent sex determination

Controls sex determination in reptiles

Three different patterns of temperature sex determination in reptiles

(EX: increasing temp results in more females)