Transcript Meiosis
Meiosis What is Meiosis? Another type of cell division Production of gametes • Sperm • Eggs Chromosome Number Homologous – one chromosome from each parent A cell that has both sets of homologous chromosomes is diploid (2n) – where ‘n’ is the number of different chromosomes A cell that contains only one of each chromosome is haploid (n) Chromosome Number cont. Gametes are haploid… If the sperm or egg were diploid, the zygote (fertilized egg) would have too many chromosomes • 46 + 46 = 92 Because the sperm or egg are haploid, the zygote has the correct # • 23 + 23 = 46 Phases of Meiosis Meiosis involves two divisions in which the chromosome number will be cut in half • Meiosis I • Meiosis II Meiosis I Synapsis – the pairing of the homologues Interphase I – cells make copies of the DNA Prophase I – each chromosome pairs with the corresponding homologue forming a tetrad (4 chromatids) • Crossing-over may occur, where portions of the chromatids are exchanged Meiosis I cont. Metaphase I – the homologous pairs line up at the equator Anaphase I – one homologue from each pair goes to each pole Telophase I & Cytokinesis – nuclear membranes form & the cell divides into two cells Meiosis II No Interphase between Meiosis I & Meiosis II Meiosis II is essentially identical to Mitosis (except at the end there will be 4 haploid daughter cells) Males vs. Females In males, the gametes that are formed are the sperm 4 sperm are produced per parent cell In females, the gametes that are formed are the eggs 1 egg is produced per parent cell Each division of the cell is uneven Males vs. Females cont. Mitosis vs. Meiosis Mitosis Meiosis Type of Cell Regular body cells Sex cells only # of divisions 1 2 # of daughter cells 2 4 Diploid (identical to parent) Growth & repair Haploid (different from parent) diploid/ haploid purpose reproduction Fun Meiosis Facts! The egg cell is the largest cell humans produce! Sperm cells are the smallest cells produced by humans! Human Females are born with all of the eggs they will have in there lifetime. Males will continue to make sperm cells throughout their life. THE END!!!