II. 9-7-10 Processes A. Meiosos 1. Process by which immature gametes mature and become capable of reproducing - F: eggs mature in ovaries (1 egg every 28 days). Ovulation: release of mature egg from ovary - M: Sperm mature in testes (daily). Released during ejaculation 2. Determines which genes parents pass on 3. Steps of meiosis: - Members of each chromosome pair line up - Each member of pair duplicates (92 chromosomes) - Crossing over segments exchange (not with XY). Creates genetic variability by making each gamete different. Each Mom/Dad can produce millions of combinations. - 2 from each pair go to the right, and 2 go to left. - Cell splits into 2 unattached cells. (2 cells/ 23 pairs (46) in each cell) - 1 from of each pair goes to right and 1 to left - Each cell splits into unattached cells (4 mature cells/ 23 individual chromosomes in each/ mature egg: 22 autosomes and one X chromosome/ Mature sperm: 22 autosomes and either X or Y) - End of Meiosis B. When mature sperm penetrates (fertilizes) mature egg: 1. Called "zygote" 2. Zygote: - 23 pairs chromosomes - As zygote develops, it has the same 23 pairs in all body cells (except mature gametes) 3. F: Typically, only 1 of the 4 mature eggs is viable (or more than 1 immature egg matures), and both fertilized, get fraternal twins (dizygotic) C. Mitosis: process by which zygote matures into baby Members 1. of chromosome pairs line up 23 pairs (46) 2. Duplication (92) 3. Identical duplicates go to opposite sides of cell 4. Cell divides into 2 attached cells. Each cell has 23 pairs (46) 5. Steps 1-4 repeat until birth and through life 6. Crossing over? NO! Baby's genes finalized when sperm penetrates egg 7. What if cells split apart in #4? Identical twins (monozygotic) III. Types of genetic traits A. Simple Mendelian: trait determined by 1 gene pair
1. Recessive in order to have a recessive trait, all relevant alleles must say you will have trait 2. Dominant in order to have a dominant trait, only one allele needs to say you will have trait 3. Co-dominant the phenotype is a combination of both alleles (AB blood type) - Ex. Autosomal recessive: cystic fibrosis, Sickle-cell, TaySachs, PKU, some MD. - PKU autosomal recessive - P = allele produces enzyme that metabolizes phenylanaline - p (lower case p) = allele fails to produce enzyme - PP = homozygous dominant has enzyme - pp = homozygous recessive - Pp = heterozygous has enzyme - Ex. Autosomal dominant : BFNC (newborn epilepsy), Hungtington's disease (HD), Some MD - With dominant traits, can you be a carrier? NO (w/caveat) - Most disorders are: recessive, why? If you have bad dominant allele to pass on, you have disease, which limits reproduction. With recessive, heterozygotes generally healthy.