Sex determination

What determines the sex of an animal

Its ability to produce a specific gamete (sperm or oocyte) and associated traits

what is sex determination

process where embryonic gonads develop into testes or ovaries

what is sexual dimorphism

distinct, non-overlapping traits between males and females (size, color)

What is environmental sex determination

sex determined by environmental factors (temperature)

What system do mammals use

XY system → males XY, females XX

What systems do birds use

ZW system → males ZZ, females ZW

What is XO system

Males XO, females XX (some insects)

What is a bipotential gonad

undifferentiated gonad that can become testes or ovaries

where does the gonadal ridge form

near embryonic kidneys (mesonephros)

what are PGCs

cells that give rise to gametes

where do PGCs originate

yolk sac and allantois

what happens if PGCs don’t reach gonadal ridge

They die

what gene determines male development

SRY gene on Y chromosome

What does SRY produce

Testis- determining factor (TDF)

What happens without SRY

ovaries develop

What hormones drives male internal/external genitalia

Testosterone → converted to DHT

What does DHT do

develops male external genitalia

What do Wolffian ducts become

Male reproductive tract

What do Müllerian ducts become

females reproductive tract

What causes Müllerian duct regression in males

Anti-Müllerian hormone (AMH)

What happens without testosterone

• Müllerian ducts develop

• prevents reversal and maintains gonad identity

what controls sex in ESD species

temperature, stress, environment

what regulates this at molecular level

epigenetic changes (methylation)

What are DSDs

Abnormal sex development (genitalia, gonads, fertility issues)

What is Turner’s syndrome

XO → female with underdeveloped reproductive organs

What is Klinefelter’s syndrome

XXY → phenotypic male with impaired spermatogenesis

What are intersex individuals

individuals with mixed male/female traits

examples of sex reversal condition

polled intersex syndrome (goats)

what is parthenogenesis

development of embryo from unfertilized egg

does parthenogenesis occur in mammals

No (due to genomic imprinting)