Sex Determination

What do testes produce?

Sperm and androgen

Where does sperm develop?

Seminiferous tubules

What do ovaries produce?

Haploid oocytes and estrogens

Where do oocytes mature?

Inside ovarian follicles

Fusion of oocyte and sperm to form a zygote

Fertilization

Supports fetus during pregnancy

Trophoblasts

Forms the fetus

Inner cell mass

Which parent determines the offspring’s sex?

Father

Environmental temperature influences sex development in some species?

Temperature dependent sex determination

Chromosomal sex established at fertilization

Genotypic sex

What are the three stages of sexual differentiation?

Chromosomal sex, gonadal sex, phenotypic sex

Whether undifferentiated gonads develop into testes or ovaries

Gonadal sex

Development of external reproductive structures

Phenotypic sex

Initiates testis development from undifferentiated gonads

SRY gene

What are the two major hormones secreted by the developing testes?

Testosterone and anti-Mullerian hormone (AMH)

Stimulates Wolffian ducts to develop into the male duct system

Testosterone

Stimulates development of external male structures

Dihydrotestosterone

Causes regression of the Mullerian ducts

AMH

Develops into ovaries

Undifferentiated gonads in an XX fetus without SRY

What happens to the Wolffian and Mullerian ducts without testosterone and AMH?

Wolffian ducts regress; Mullerian ducts develop into female structures

How can chromosomal sex differ from phenotypic sex?

Mutations can alter gonadal development or hormone responses

What causes complete androgen insensitivity syndrome (AIS)?

A mutation in the androgen receptor gene

How does complete AIS affect an XY individual?

They cannot respond androgens and develop a phenotypically female appearance

Inefficient testosterone and DHT production in a chromosomally male individual; male development may occur at puberty

Gonadal intersexuality

Equalization of X-linked gene product levels between sexes

Dosage compensation

Only one X chromosome is active in each female mammalian cell

Lyon hypothesis

Is X chromosome inactivation random or nonrandom?

Random

When does X chromosome inactivation occur?

Early embryonic development

Is X chromosome inactivation permanent?

Yes, except in germ cells

An inactivated X chromosome

Barr body

How many Barr bodies are in a typical XX cell?

One

Different cell populations express different X-linked alleles because different X chromosomes are inactivated

Mosaic X chromosome expression

Why can female cats be calico?

Random X inactivation creates patches expressing orange or black coat color alleles

Coats an X chromosome and helps inactivate it

XIST RNA

Why can identical twin females differ in an X-linked trait?

Random X inactivation can produce different patterns of gene expression

A trait expressed in both sexes but differently; it can be dominant in one sex and recessive in the other

Sex influenced trait

A trait whose genes are inherited by both sexes but expressed in only one sex

Sex limited trait