University:
Amherst College
Course:
BIOL 220 | Developmental Biology
Academic year:

2022
Views:

80

Pages:

12
Author:

Kaeden Hicks

Sex Determination • Most animal species are dioecious – 2 sexes with different gonads • Females: produce eggs in ovaries • Males: produce sperm in testes • Exception • Hermaphrodites: have both types of gonads • Many animals also differ in secondary traits What Determines Sex? • Individual differentiates into male or female • Causes – Genetic factors (sex chromosomes) – occur at fertilization – Environmental factors – occur after fertilization How Do Vertebrate Gonads Develop? • Gonad differentiation – first morphological difference between males and females • Gonads develop from intermediate mesoderm • Paired structures What is a Bipotential Gonad? • Indifferent gonad develops – 4-6 wks in human = “bipotential stage” – genital ridge forms next to developing kidney (mesonephric ridge) Structure of the Indifferent Gonad • Sex cords form – Columns of epithelial cells penetrate mesenchyme – Primordial germ cells migrate from posterior endoderm – Become surrounded by sex cords What is the Fate of the Sex Cords? • Initially in central area (medulla, medullary) – Will develop in male – Proliferate • In outer area (cortex, cortical) – Develop in female • Normally binary choice Differentiation of the Gonad • Into testes or ovaries – primary sex determination – does not involve hormones network of internal sex cords (at puberty: --> seminiferous tubules, Sertoli cells new cortical sex cords cluster around each germ cell Male Differentiation • Male sex cords or testis cords proliferate and cortex becomes thick layer of extracellular matrix • Male germ cells inhibited from entering meiosis • Secrete factors causing cord cells to become Sertoli cells Female Differentiation • Female germ cells in cortex enter meiosis • New sex cords form there and form clusters • Germ cell becomes egg • Cord cells become granulosa cells • Surrounnding mesenchyme cells become thecal cells • Thecal + granulosa = follicle Male Ducts • Provide exit for gametes – In males remnants of mesonephric kidney called Wolffian ducts – Differentiates into vas deferens and epididymis • Supported by testosterone – Made by Leydig cells – Leydig cells come from mesenchyme Female Ducts • Also provide exit for gametes – In females, Mullerian duct part of gonad – Differentiates into uterus, oviducts and upper vagina • Supported by estrogen – Destroyed in males by anti-Mullerian duct hormone kidney hormones vas deferens Secondary sex determination oviduct

Sex Determination Part 1

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