Meiosis- gamete formation Mader Chapter 17.3

Mitosis does not alter the chromosomal makeup of cells

Chromosome number must be reduced when gametes are produced

Meiosis separates homologous chromosomes

There are 2 N Possible arrangements of homologues Humans have 23 pairs of homologous chromosomes N=23 There are 2 23 possible arrangements of homologues = 8,388,608 Four of the eight possible arrangements for a N = 3 organism are shown above. Each Arrangement  2 gametes so there are 8 possible gametes!

Crossing over generates even more diversity

Meiosis Separates homologous chromosomes Chromosome number goes from 2N  N Generates a very diverse set of gametes each of which contains a nearly unique set of maternal and paternal genes

Spermatogenesis

Human ova are ovulated arrested in meiotic prophase II

The human life cycle