Bio 1201 Notes

* Meiosis – cell division for gamete production * In specialized tissues * Produces cells with the 1n chromosome number * Two Divisions * Meiosis I separates homologous chromosomes * Meiosis II separates sister chromisis * Asexual Reproduction * Mitotic division * Identical offspring * Sexual Reproduction * Fuse gametes from parents (syngamy) to produce a zygote * Each parent contributes half the genetic material * Increase the diversity of offspring * Different combinations of chromosomes * Increase the potential type of diversity * Stages of Meiosis * Prophase I * Metaphase I * Anaphase I * Telophase I * Prophase II * Interphase * As in mitosis * During S phase DNA is replicated giving rise to chromosome consisting * Prophase I * Spindle formation * Breakdown of nuclear envelope * Chromosomes condense * Each chromosome consists of 2 chromatids from S phase of interphase * Homologous chromosome pairs lie next to one another * Crossing over of chromatids between pairs (chiasma formation) * Crossing Over * Called chiasma (chiasmata – plural) * Hold homologous chromosomes together * Can result in a physical exchange of genetic material between homologs * Recombinant chromosomes result * Increase genetic diversity * Meiosis * Occurs in cells that give rise to gamets * Produces cells with the haploid (1n) chromosome number * Mitosis occurs in somatic cells and produces diploid (2n) cells * Metaphase I * Chromosome pairs line on equator of spindle * Kinetochores of sister chromatids are attached to fibers going to the same pole * Anaphase I * Homologous chromosome pairs separate * Sister chromatids remain together * Telophase I * Depending on the species * Nuclear membrane may reform * Cytokinesis may occur * Meiosis II * Cell division like mitosis