Meiosis

Diploid number of chromosomes reduced to haploid level. Random assortment of chromosomes along metaphase plate results in different combinations of alleles in each gamete. Crossing-over also results in new allelic combinations within gametes.

First Metaphase - chromosome alignments are independent events for each chromosome gametes: AB:ab:Ab:aB.

Random alignment of chromosomes on metaphase plate results in equal proportions of gametes. Actually, each homologous chromosome consists of two sister chromatids. Two homologous chromosomes consisting of two sister chromatids each sums to a tetrad or bivalent.