1. Meiosis: production of gametes One diploid precursor cell; DNA replication Two rounds of cell division Four product cells; each is haploid with one set of genetic information. New combinations of alleles – Independent assortment – Crossing over When does meiosis begin: a difference between males and females

2. Meiosis Synapsis

3. 2 23 = number of possible combinations of maternal and paternal chromosomes In gamete production.

4. Sexual reproduction and genetic variation Independent assortment Crossing over

5. Mutation at the chromosome level Synapsed chromosomes fail to disjoin (nondisjunction) Normal development based on balanced set of genetic information Aneuploidy: + or – of single chromosomes from a diploid set Trisomy: e.g., Down syndrome Monosomy: e.g., Turner’s syndrome The unusual timing of synapsis In human females.

6. http://highered.mcgraw- hill.com/olcweb/cgi/pluginpop.cgi?it=swf::5 35::535::/sites/dl/free/0072437316/120076/ micro04.swf::DNA%20Replication%20Fork http://www.youtube.com/watch?v=D3fOXt4 MrOM&feature=related