Gametogenesis Flashcards
what are epigenetic effects (3) main points
- non-DNA changes
- can affect gene expression
- can influence lifetime outcomes
what are the gonads
- ovaries
- testes
where do the gonads develop
at the genital ridge
which migrating cell populations give rise to the gonads. which also multiply?
- primordial germ cells - these also multiply
- germinal epithelial cells
- mesonephric cells
what are gonads
specialised organ that produces the gametes (sperm or oocyte / egg) and sex hormones of organism
where do the cell populations that give rise to gonads go
they migrate to the genital ridge
what determines if testes or ovaries (gonads) develop
what chromosome sperm is carrying
- X chromosome -> ovaries develop
- Y chromosome -> testes develop
why does Y-chromosome carrying sperm result in testes
SRY gene on Y chromosome (sex-determining region of Y chromosome) ‘makes’ a testis
what chromosome is the egg carrying?
X chromosome
what are the gamete precursors
primordial germ cells
what are gametes
- sperm
- oocyte (immature egg cell) or egg
from the cell populations that give rise to gonads which do and don’t contain SRY gene
germinal epithelial cells express SRY
primordial germ cells and mesonephric cells do not express SRY
what do the cell populations that give rise to the gonads contribute to in testis formation
- primordial germ cells -> gamete precursors: give rise to sperm and egg
- germinal epithelial cells -> give rise to primitive sex cords and Sertolli cells that enclose the primordial germ cells (prespermatogonia)
- mesonephric cells -> give rise to the vasculature, Leydig cells, seminiferous tubules
what is spermatogonia
- spermatogonia = germ cells responsible for producing sperm cells (spermatozoa) thru spermatogenesis
what do Leydig cells produce
androgens (male sex hormones; class of steroid hormones) - incl testosterone, DHT
what do the cell populations that give rise to the gonads also contribute to in ovary formation
- primordial germ cells -> gamete precursors: give rise to sperm and egg
- germinal epithelial cells -> cluster around PGCs (oogonia) to form primordial ovarian follicles
- mesonephric cells -> give rise to the vasculature, stroma
what occurs after gonad formation
internal genitalia
how do internal genitalia form
two unipotential primordia (organ/tissue in earliest stage of development) located next to gonads give rise to internal genitalia
- unipotential - ability of primordia to give rise to a specific type of organ or tissue not into multiple types; here: two early developmental structures specialised and predetermined to develop into internal genitalia only
what 2 main hormones to foetal testis (gonads) make & their function
- androgens in Leydig cells -> stimulate Wolffian ducts (male) to make epididymis, vas deferens, prostate
- anti-mullerian inhibitor (AMH) in sertoli cells -> causes mullerian ducts to regress (preventing formation of female internal reproductive structures)
what is the role of the mullerian ducts
- arise during early embryonic development
- paired embryonic structures
- present in both male and female embryos
- crucial role in development of reproductive system, esp in females
what happens to mullerian ducts in females
absence of AMH, mullerian ducts become oviducts, uterus, cervix, upper vagina
what occurs after internal genitalia formation in males
- external genitalia form in presence of androgens
- bipotential precursors become scrotum and penis in
- bipotential precursors: structures in early embryonic development that have potential to differentiate into either of 2 distinct cell types
gametogenesis same but different
- gametogenesis is process of producing gametes
- spermatogenesis in males & oogenesis in females
- meisosis of spermatogonia and oogonia - into mature gametes - sperm or eggs- capable of fertilisation ie/ diploid cell (46) reduced to haploid cell (23)
BUT timing is different
how is gametogenesis different explanation
- sperm produced continuously from puberty until death (decline in sperm quality overtime) ; spermatogenesis occurs at puberty
- oogenesis starts before birth => number of oocytes (potential eggs) fixed at birth. Oocytes suspended at Prophase 1 in meiosis at birth until puberty
- meiosis resumes at ovulation (continues till most oocytes been ovulated or lost to atresia)
- meiosis completed following fertilisation (ovulated oocyte that’s fertilised)
=> 99% oocytes do not ovulate and lost through atresia (oocyte not chosen each menstruation) by time of menopause (~50yrs old)
