Diploid

-A cell or an organism consisting of two sets of chromosomes

-one set from the mother and another set from the father

-Somatic cells (body cells) are diploid

-In humans, the diploid number is 46 (23 from mom, 23 from dad)

-Symbolized as 2n

Haploid

-A cell or organism consisting of one set of chromosomes (half)

-Gametes (sex cells) are haploid

-In humans, the haploid number is 23 (egg=23, sperm=23)

-Symbolized as n

Meiosis

-cell division of the gametes

-halves the number of chromosomes

-occurs in all sexually reproducing organisms

-there are two stages of meiosis (two divisions); meiosis I and meiosis II

-Meiosis in males: spermatogenesis

-Meiosis in females: oogenesis

-begins with a germ cell which contains 46 chromosomes

23

-ends with 4 gametes which contain 23 chromosomes

Homologous Chromosomes

-chromosomes that are paired during meiosis

-they consist of four chromatids total

-One pair is inherited from an individual’s father, the other pair is inherited from the mother

-identical in shape and size, and gene location

-only present during meiosis

-during meiosis they swap genes (cross over) in order to diversity gametes

Drawing:

Crossing Over

-a process in which homologous chromosomes exchange genes

-important for genetic variation (if not for crossing over, all of an individual’s gametes may be identical)

-occurs during Prophase I