Lecture Notes 9/11/08

9/11 Cell Reproduction Meiosis in Mammals - producing sperm In testes of males - spermatogenesis Result is 4 haploid cells = spermatids ( undergo differentiation to become sperm Sperm head contains only DNA Production begins w/ puberty & continues throughout male?s life Oogenesis in Mammals - producing eggs Meiosis in ovaries of females results in 4 haploid cells - 1 egg (ovum) & 3 polar bodies Eggs contain chromosomes & all the cell components needed for the new zygote - mitochondria, golgi, ER, extra nourishment, etc. Females born w/ all their eggs (primary oocytes) already produced Development arrested in Meiosis I by birth, begins again at puberty & is arrested in Meiosis II until fertilized With fertilization, secondary oocyte completes meiosis II Unfertilized eggs continue to stay in ?dormant? state Women can have children 20-30 years - older eggs more likely to result in abnormal births (ex: Down Syndrome) Mitosis - rates & differentiation Fastest in bone marrow - to make blood cells, slowest in nervous system As cells differentiate (become specialized) they often lose the ability to divide (as in nervous tissue) Totipotent cell - one that is capable of producing daughter cells that can become any cell type - each one has the ability to develop into a new embryo Stem Cells Some cells in nearly all tissues that are less differentiated than other cells (very few in nervous system) Can replace damaged cells Over 200 specialized cells in humans Apoptosis - programmed cell death Cells receive a death signal and begin to dismantle Ex: old or damaged cells, webbing between fingers in embryo, peeling away of sunburned skin cells Healthy organs are in balance with mitosis and apoptosis