BIO 111 Lecture 18: BIO111 11/14/16
Document Summary
Chapter 15 part two meiosis & sexual reproduction. In sexual reproduction, genetic information from two parents is mixed to make diverse offspring! When the haploid sperm and haploid egg fuse a diploid fertilized egg (zygote) is produced. Haploid cells produced from a cell that was originally diploid. Meiosis key differences: homologous pairs form a bivalent or tetrad, crossing over gene swapping . Overall effect increase genetic possibilities & variety in offspring: bivalent or tetrad. Homologous pairs of sister chromatids associate; lie side-by-side to form a bivalent (aka tetrad) Number of crossovers carefully controlled by cells: crossing over. Random alignment of the homologous chromosomes at the metaphase plate (during metaphase i of meiosis i ) Creates so many possibilities for gene combinations in offspring! 223 different ways chromosomes could line up in meiosis. Not even including variation due to crossing over!! Two rounds of division: meiosis i and meiosis ii. Nuclear envelope begins to dissociate into vesicles.