Sexual reproduction in mammals Flashcards
Germ cell
diploid cells which give rise to gametes through meiosis
Polar body
a small haploid cell that is formed at the same time as an egg cell during oogenesis, but generally does not have ability to be fertilised
Germinal epithelium
a single layer of cells that undergoes regular mitosis, producing other cells
Gametogenesis
process of gamete production
- the female and male gametes are produced in organs called gonads
what is the female gonads called ?
ovaries - produces ova
what is the male gonads called ?
testes - produces spermatozoa
Spermatogenesis
- germ cells divide several times by mitosis to form spermatogonia
- spermatogonia grow without further division to form primary spermatocytes
- primary spermatocytes undergo the first meiotic division to form secondary spermatocytes
- secondary spermatocytes undergo the second meiotic division to form spermatids
- spermatids differentiate and grow to form mature spermatozoa
Oogenesis
- germ cells divide several times by mitosis to form oogonia
- only one oogonium continues to grow to form a primary oocyte
- the first meiotic division forms one secondary oocyte and one polar body
- the second meiotic division of the secondary oocyte forms one haploid ootid and one polar body - than forms two more polar bodies
- degenerate and die as the ootid develops
what does the ovum contain ?
- zona pellucida
- haploid nucleus
- cortical granules
- follicle cells
Zona pellucida
protective coating that the sperm have to penetrate in order for fertilisation to occur
main purpose: to prevent polyspermy
Haploid nucleus - ovum
full set of chromosomes is restored at fertilisation
Cortical granules
release substances which cause the zona pellucida to harden, forming a tough fertilisation membrane
Follicle cells
forms protective coating around the egg
Spermatozoa - key features
- mitochondria
- acrosome
- haploid nucleus
Mitochondria
provide energy for rotation of the flagellum which enables the cell to move
Acrosomes
contain digestive enzymes which break down the zona pellucida and allow sperm to penetrate the egg
Haploid nucleus - spermatozoa
allows the restoration of the full set of chromosomes at fertilisation
Process of fertilisation
- the sperm head contacts the zona pellucida and the acrosome reaction occurs
- the sperm head fuses with the cell membrane of the egg cell, thus allowing the sperm nucleus to enter the egg cell
- the cortical reaction occurs
- nuclei fuse and a full set of chromosomes is restores, thus forming a diploid zygote
Acrosome reaction
- acrosome swells and fuses with membrane of secondary oocyte
- releases hydrolytic enzymes which hydrolyse the zona pellucida
Cortical reaction
- head of sperm is engulfed and this causes by microvilli to increase in calcium ions
- cortical granules fuse with the membrane
- hardens - prevents polyspermy
Following fertilisation…
- the zygote is moved down the oviduct by ciliary action
- the zygote will undergo several mitotic divisions to transform a single zygote to form a solid ball of cells - cleavage
- At day 3, cleavage has transformed a single zygote to form a solid ball cells called morula
- At day 4, the solid ball of called morula have now transformed into a blastocyst
Blastocyst
- inner cell mass called blastomeres
- surrounding outer layer called the trophoblast
- a fluid filled cavity called the blastocoele
