Meiosis Division of sex cells
Mitosis vs. Meiosis • Mitosis: start with one diploid cell, end with two identical diploid cells • Somatic cells (most cells in your body) • Meiosis: start with one diploid cell, end with four different haploid cells • Gametic cells (sperm and egg)
Humans are diploid • Ploidy refers to sets of chromosomes in an organism • Diploids have two sets of chromosomes, one from each parent • Each homologous pair contain the same genes in the same loci (locus) or location
Gametes are haploid Why?
Spermatogenesis • Each primary spermatocyte divides to form 4 mature sperm • This process is ongoing in reproductive aged men
A mature sperm cell has shed cytoplasm • The parts of the sperm are developed to assist in delivering the DNA to an oocyte (egg)
Oogenesis • One primary oocyte divides and produces only one mature egg • Primary oocytes arrest at Prophase 1 by birth – meiosis I continues after puberty, but meiosis II only proceeds if fertilization occurs
Meiosis is uneven- most of the cytoplasm is passed on to the oocyte. • Cell structures from this cytoplasm are responsible for cell function for the first few days of development. • Mitochondria is only inherited from mother cell.
During meiosis, homologous chromosomes can exchange pieces Crossing over, results in recombination of genes