Sex chromosomes

Sex Determination (Dev. Bio)

• Governed by chromosomes

  • XX, XY (sperm content determins sex of embryo)

Male/Female difference

• repro systems

• external phenotype → sexual dimorphism

• behavour → testosterone induced aggression

• Metabolism under hormonal control

• influenced by env → temp, dominance (red deer)

• nutrition (humans)

• toxins and psychological stress (humans)

• mother manipulation via sperm selection

  • genetic profiling

  • sperm surface markers → CD52 proportional to DNA integrity (more = better)

• X vs Y sperm differentiation → morphology, protein expression, microRNA

• X and Y sperm induce sex specific gene expression in female tract

Bi-potential embryonic gonad - have both duct systems

• active gene directed processes determine which system persists

• Wolffian

• Mullerian

Wolffian male or female

Male

(Wolfgang Amadeus Mozart)

SRY (sex-determining region) gene on Y chromosome

• produces TDF (testes determining factor protein) protein

  • activates SOX-9 expression

    • testicular development

Two celll types in testes

expression of SOX9 induces following reaction from testicular cells

Sertoli cells

• produce sf1 (steroidogenic factor 1) → causes mullerian duct regression by upregulating antimullerian hormone

Leydig cells

• produces sf1 → testosterone production

• → wollfian duct → internal repro (epididymis, vas deferns, accessory glands)

• → urethral folds → external repro (penis etc)

Mullerian male or female

Female

• default

• absence of significant testosterone from foetal testes causes mullerian to develop

A DAX1 gene on each X chromosome

• downregulates sf1

• then WNT4a gene expressed in bi-potential gonad

  • stimulates gonad conversion to ovary

    • follicular and theca cells → in follicles → oestrogen production

  • therefore mullerian duct persists and develops

  • oestrogen production → internal female genitalia

    • uterus, oviduct, cervix, upper vagina

Gonadal dysgenesis → XY → female phenotype

• 2 copies of DAX1 in 1 X chromosome

Female internal repro

Presence of dysfunctional testes that cannot produce testosterone