Sex determination and differentiation

what is sex determination

• development decision that directs an uncommitted gonad to develop as testis or ovary

which chromosome contains sex-determining gene in mammals

• Y chromosome

what gene on the Y chromosome controls sex determination?

• SRY gene

which animals’ gender is affected by the environment?

• reptiles

• fish

• amphibians

which hormones do the testes produce

• testosterone

• inhibin

what hormones do the ovaries produce?

• oestrogens

• progesterone

• inhibin

what’s a genotype

• the genetic make-up of an organism

what is a phenotype

• the observable characteristics of an organism

where do germ cells migrate to in the pregondal phase?

• yolk sac

what is primary sexual differentiation

• differentiation of reproductive tissues, reflecting nature of gonads

what is secondary sexual differentiation

• development of secondary sexual characteristics

  • marks sexes phenotypically distinct

what are the 3 levels of sexual dimorphism

• genetic

• gonadal

• phenotypic

what are the 3 phenotypic sexual dimorphisms?

1. external features

2. internal sex organs

3. sexual differentiation of the brain

what are the 2 sexual differentiations as a result of the brain causing sexual dimorphism?

• sexual behaviour

• pituitary gonadotrophin secretion

what feature in neutrophils is caused by XX chromosomes?

• Barr body

what gene on the male Y chromosome guides testicular development?

• SRY gene

outline the pathway of female tract development, starting with No SRY protein

1. ovaries develop

2. no AMH

3. paramesonephric ducts → oviducts, uterus, cervix + part of vagina

what is the SRY gene known as?

• testes determining factor

what is the pathway of male development from the TDF (testes determining factor

1. testes develop

2. sertoli cells secrete AMH

• AMH → Leydig cell diferentiation →

  • testosterone → male ducts develop

  • dihydrotestosterone → penis, scrotum + accessory glands develop

• PMN ducts degenerate

how does the surge centre in the female brain develop?

• alpha-fetoprotein binds to oestradiol produced in the ovaries

• can’t cross BBB

• surge centre develops

what does the binding of alpha-fetoprotein to oestradiol protect the female brain from?

• the masculinising effects of oestradiol

how is the brain development affected in the male?

• testosterone passes through the BBB

• converted to oestradiol and dihydrotestosterone by aromatase

• this inhibits surge centre development

• oestradiol masculinises the brain

what is AMH?

• anti-mullerian hormones

what is AMH produced by?

• sertoli cells

what does AMH cause?

• regression of paramesonephric ducts

how does the affect of AMH compare in females vs males

• females = no AMH → PMN develop

• males = AMH → suppresses PMN ducts → MN carry on developing

what are the clinical uses of detecting blood AMH?

1. ovarian remnant syndrome

2. cryptorchidism

3. sertoli cell tumour

4. granulose cell tumour

5. sex reversal

6. intact vs castrated males

what methods can we use to detect cryptorchidism in animals?

• AMH test

• hCG test

• oestrogen levels

• testosterone levels

• ultrasonography

what happens if the male embryo fails to produce AMH?

• PMDS

• female reproductive organs are present with male external genitalia

what is PMDS?

• persistent-mullerin deficiency syndrome

what role does testosterone have in the formation of external genitalia?

• it maintains the mesonephric ducts and induces formation of male external genitalia

what happens if male embryo fails to make enough testosterone?

• foetal testosterone deficiency - disrupt normal development of reproductive tissues

which hormone induces female external genitalia development?

• oestrogen

where do germ cells migrate from and to?

1. epiblast

2. yolk sac

3. hindgut

4. dorsal mesentery

5. genital ridges

6. gonads

which cells in the body determine gender?

• germ cells

what is the proliferation of XY germ cells up until birth (3)?

• mitosis during migration

• growth arrests at the gonad

• remain in G0 in the testes until after birth

what happens to the G0 XY germ cells in the testes after birth?

• resume cell cycle

• meiosis forming haploid spermatozoa

• sertoli cells nuture them and spermatogenesis is complete at puberty

what induces the G0 phase in XY germ cells?

• meiosis inhibitory factor produced by sertoli/myoid cells

what is the proliferation pathway of XX germ cells up until birth

1. mitosis as they migrate to female genital ridge

2. enter ovary

3. initial stages of meiosis I and arrest at prophase I by birth

4. surrounded by single layer of granulosa cells → primordial follicles

what happens to XX germ cells after birth and until puberty/

• follicle development continues

• oocytes remain arrested

what are thecal cells??

• ovarian cells that synthesise androgens

what are follicular cells

• essential cells in the development and maturation of oocysts