02.20.10 Lecture 16 - Mitosis II

Meiosis is a specialized type of cell division that produces haploid cells Diploid cells - have 2 copies of each chromosome. The somatic cells in an organism are diploid and are produced by mitosis (1 cell --> 2 genetically identical copies). Haploid cells - have one copy of each chromosome. Reproductive cells of the gem line (sperm and eggs) are haploid and are produced by meiosis (1 cell --> 4 genetically dissimilar cells).

Sexual reproduction involves both haploid and diploid cells

Homologous chromosomes pair before lining up on the spindle during meiosis

Maternal and paternal chromatids recombine in paired chromosomes to form chiasma Sister chromatids are held together by cohesins

Chiasmata ensure proper segregation of chromosomes in meiosis

Kinetochores on each sister chromatid function independently in meiosis II (like in mitosis)

Meiosis increases genetic variability During meiosis, maternal and paternal chromosomes parceled at random, therefore, many genetically different gametes may come from one individual Exchange of genes during crossing over further enhances genetic variability between chromosomes

2 sources of reassortment generate new combinations of chromosomes

Errors during chromosome segregation result in gametes with incorrect numbers of chromosomes