DEVELOPMENT OF GONADS

Presented by

Prachee Rajput

DEPT OF ZOOLOGY AND APPLIED AQUACULTURE BU BHOPAL

M.SC 4TH SEM

SYNOPSIS

• INTRODUCTION• CHROMOSOMAL ORGANIZATION• DEVELOPMENT OF BIPOTENTIAL GONADS• MOLECULAR BASIS OF GONADIAL DEVELOPMENT• CONCLUSION• REFRENCES

INTRODUCTION

Sex is determined genetically by two chromosomes,called the sex chromosomes.In humans and many other mammals,the sex chromosomes are called X and Y chromosomes.The Y chromosomes is necessary and sufficient for the production of testis.In both sexes,the gonads have dual function:the production of germ cells and the secretion of sex hormones.The testes secrete large amount of androgens,principally testosterone,but they also secrete small amounts of estrogen.The ovaries secrete large amount of estrogens and small amounts of androgen.The ovaries also secrete progestrone which helps the uterus for pregnancy.

CHROMOSOME ORGANIZATION

X and Y chromosomes determine the sex of humans and many other mammals.The Y chromosomes is necessary for the production of testis,and the testis determining gene product is called ,SRY(for sex determining region of the Y chromosome).SRY is a DNA binding regulatory protein.Male cells contain X and Y chromosomes (XY pattern) where as famale cells contain two X chromosomes (XX pattern).Each normal ovum contains a single X chromosome,but half the sperm contain a X chromosome and half contain Y chromosome.When a sperm fertilizes an ovum,an XY pattern results into genetic male.And when fertilization occurs with an X containing spem,an XX pattern results in to genetic female.

DEVELOPMENT OF BIPOTENTIAL GONADS

On each side of the embryo ,a primitive gonad arisesfrom a genetial ridge,a condensation of tissue near the adrenal gland.The gonad develops a cortex and a medulla.Untill the sixth week of development ,these structures are identical in both sexes.In genital males the medulla develops during seventh and eight weeks into testis,and the cortex regresses.Leydig and sertoli cells appear and testosterone and mullarian inhibiting substances are released.In genetic females the cortex develops into ovary and the medulla regresses.In normal female fetus ,mullerian duct system develops into uterine tubes and a uterus.In male fetus wolffian duct system develops into external genetalia.

MOLECULAR BASIS OF GONADIAL DEVELOPMENT

On the shorter arm of Y chromosome special gene is present k/a SRYgene which contains a protein called TDF(testicular determining factor) which help in development of testis.When there are functional testis in the embryo male internal and external genitalia develop.Sertoli cells secrete MIS which cause regression of the mullarian ducts.Due to development of wolffian duct male external genitelia develops.On the other hand in XX chromosome,no SRY gene is present that means no TDF protein and there fore no secretion of MIS.Thus mullarian duct develops into female genitelia.

XY XX

SRY

TDF

MEDULLA

MIF

TESTOSTERONE

TESTIS

MALE BRAIN

SRY absent

no TDF

MD

CORTEX

OVARY

ESTROGEN

FEMALE BRAIN

CONCLUSION

Thus from the discussion we came to know that TDF is produced by a gene on the Y chromosome.TDF induses the medulla of gonads to develop the testes,which produces testosterone that initiates the development of male sexual characters.And in the absence of Y chromosome no TDF is produced.The lack of TDF allows the cortex of embryonic gonads to develop in to ovaries and in the absence of testosterone embryo develops female characters .

REFRENCES

• Review of medical physiology by william F.Ganog• Endrocrinology by Hedly• Internet sources

THANK YOU