Terminology

PAR

Pseudo-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

Proteins that influence whether expression starts or not. Activators Enhancers

Speeds up transcription.

Positive gene expression.

Repressors Silencers

Slows down transcription.

Negative gene expression.

Combinatorial Control

Most genes require multiple transcription factors.

Gametogenesis

Spermatogenesis

♂ Male

• Spermatogonium -sperm them cells (2n)
• Primary spermatocyte (2n)
• Secondary spermatocyte (meiosis 1, 1n)
• Spermatids (immature sperm) (meiosis 2, 1n)
• • Sperm are mature

Oogenesis

♀ Female

• 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.