- PAR
- Psuedo-Autosomal Region
- Region on the XY chromos that have a lot of homology - at telomeres.
- Sex tetrad may recombine at the PAR
-
- SRY gene - male determining gene - may get swept up in the recombination and blur gender.
-
- The SRY gene is very close to, but not in the autosomal region.
- Transcription Factor
- ?
Gametogenesis
Male
- Spermatogenesis
- Spermatogonium -sperm them cells (2n)
- Primary spermatocyte (2n)
- Secondary spermatocyte (meiosis 1, 1n)
- Spermatids (immature sperm) (meiosis 2, 1n)
-
- Sperm are mature
- Female Oogenesis
- Oogonium - stem cells in fetus, 2n
- Primary oocyte (2n)
- Meiosis 1 stops when female baby.
- Secondary oocyte completes during ovulation (generates dud first polar body).
- Stops in metaphase II
- Ovum, 1n completes upon fertilization (generated 2 duds, second polar body).
- Polar Body
- Unviable gametes, not enough cytoplasm.
- Only 1/4 gametes are viable.
- Primary Oocytes
- Still 2n, pause for up to 50 years ??
- Trisomy 21 is viable, chance increases as maternal age reaches 35.
- Fertilization
- Joining of sperm and ovum.
- Meiosis II
- Not complete in egg until fertilization.
- Egg has mechanisms to prevent polyspermy. - multiple sperm that fertilize the same egg - zona polusala.
- In vitro fertilization - or genotype the polar body
- Human embryo grows in culture for awhile.
- Can take a single cell from the 8-cell stage embryo to do genotyping.
- Pronuclei
- Nuclei of sperm and egg come together and merge.
- Can use polar bodies from embryos derived by IVF to genotype for genetic disorders before implanting.
- Polar body 2 is most similar to viable games b/c only sister chromatids differ.