2- sexual reproduction in mammals Flashcards
order of oogenesis
oogonia -> primary oocytes -> first meiotic division -> second meiotic division -> completion of meiosis -> polar bodies
oogenesis- oogonia
primordial germ cells divide by mitosis to form oogonia during the foetal period
oogenesis- primary oocytes
- each oogonium grows and becomes a primary oocyte
- the primary oocyte enters prophase of the first meiotic division but halts
- at birth, all primary oocytes are in a state of arrested development until puberty
oogenesis- first meiotic division
at the start of each menstrual cycle, one primary oocyte resumes its first meiotic division to form a secondary oocyte and a small polar body
oogenesis- second meiotic division
- the secondary oocyte enters metaphase of the second meiotic division but halts
- the secondary oocyte is released at ovulation
oogenesis- competition of meiosis
- when fertilisation occurs, the secondary oocyte resumes its second meiotic division to form the ovum and another polar body
oogenesis- polar bodies
- they are small cells that eventually degenerate
- they serve to discard the extra set of chromosomes
spermatogenesis- spermatogonia
primordial germ cells divide by mitosis to form spermatogonia
spermatogenesis- primary spermatocytes
spermatogonia grow and become primary spermatocytes
spermatogenesis- first meiotic division
primary spermatocytes enter the first meiotic division to form secondary spermatocytes
spermatogenesis- second meiotic division
- secondary spermatocytes enter the second meiotic division to form spermatids
spermatogenesis- maturation
- spermatids differentiate and grow to form mature spermatozoa
polar body
- small cells that bud off from an oocyte which eventually degenerate
- they serve to discard the extra set of chromosomes
gonad
the organ that produces gametes
germinal epithelium
an epithelium consisting of a single layer of primordial germ cells that undergoes mitosis to produce other cells
primordial germ cells
the primary undifferentiated germ cell type that differentiates into germ cells and give rise to gametes through meiosis
oogenesis diagram
spermatogenesis diagram
events of fertilisation order
initial contact -> acrosome reaction -> enzyme release -> membrane fusion -> entry of sperm nucleus -> cortical reaction -> competition of meiosis II -> nuclear fusion
fertilisation- initial contact
glycoproteins on the sperms cell membrane and the eggs zona pellucida interact
fertilisation- acrosome reaction
the acrosome reaction is triggered. it fuses with the sperms cell membrane
fertilisation- enzyme release
the acrosome releases hydrolytic enzymes, which help digest the zona pellucide
fertilisation- membrane fusion
the sperms cell membrane and the eggs cell membrane fuse together
fertilisation- entry of sperm nucleus
the sperm nucleus enters the egg
fertilisation- cortical reaction
the cortical reaction is triggered, cortical granules in the egg fuse with the cell membrane and release enzymes that harden the zona pellucida to prevent polyspermy
fertilisation- competition of meiosis II
the egg completes the second meiotic division
fertilisation- nuclear fusion
the haploid nuclei of the sperm and ovum to form a diploid nucleus- a zygote
egg diagram
sperm diagram
corona radiata
follicle cells that form a protective coating around the oocyte
zona pellucida
- protective coating that the sperm has to penetrate through for fertilisation to occur
- prevents polyspermy
cortical granules
releases substances which causes the zona pellucida to harden, forming a rough fertilisation membrane
nucleus - egg
haploid so a full set of chromosomes is restored at fertilisation
acrosome
contains digestive enzymes which break down the zona pellucida and allow sperm to penetrate the egg
nucleus- sperm
haploid, so a full set of chromosomes is restored at fertilisation
mitochondria
provide energy for rotation of the flagella allowing the cell to move
centriole
the centriole is contributed to the zygote to allow it to undergo cell division
flagella
allows the sperm to swim towards the oocyte
early development of the embryo to blastocyst stage
1) the zygote undergoes mitosis as it moves through the fallopian tube towards the uterus
2) blastomere cells are formed
3) by day 3-4, a morula (solid ball of 16 blastomeres) is formed, it reaches the uterus
4) by day 5-9 a blastocyst (ball is filled with fluid) is formed, cell differentiation begins.
5) the trophoblasts (outer layer of cells) form the amnion, placenta and extraembryonic tissues
6) the inner cell mass (blastomeres) form the embryo
