Chapter 9: Meiosis

Meiosis serves as two major functions

1. reducing chromosome number

2. shuffling chromosomes in the cell to produce genetically different gamates.

Homologous Chromosomes

members of a pair of chromosomes and contain the same genes for the same traits.

called Homologues

Alleles

Alternate forms of a gene

Both females and males have how many pairs of chromosomes?

23 pairs = 46 total chromosomes

Diploid (2n)

Haploid (n) in gamates

23 total chromosomes

Female is

XX

Male is

XY

Life Cycle

in sexually reproducing organisms this refers to all the reproductive events that occurs from one generation to the next.

Involves mitosis and meiosis

Somatic Body Cells

are diploid cells

Meiosis reduces the…

numer from diploid to haploid

Spermatogenesis produces

sperm in the testes

Oogensis produces

Eggs in the ovaries

Egg and Sperm join to form

diploid zygote

Meiosis I

Homologous pairs line up during synapis resulting in tetrad.

Homologous chromosomes of each pair then separate.

Meiosis II

No duplication of chromosomes.

Chromosomes are dyads — composed of 2 sister chromatids.

Sister chromatids are separated.

2 daughter nuclei separate.

Crossing-over

the swapping of genetic material that occurs in the germline cells, during the formation of egg and sperm. Paired chromosomes from each parent aligns so that the similar DNA sequences from the paired chromosomes cross over one another.

Crossing over can only occur between what chromosomes?

Homologous Chromosomes

Prophase I

Metaphase I

Anaphase I

Telophase I

Cytokinesis I

Prophase II

Metaphase II

Anaphase II

Telophase II

Cytokinesis II

Result of Meiosis I

2 different daughter cells are formed. Each with half the number of chromosomes as the parent cell.

Called Reduction division.

Result of Meiosis II

4 non-identical haploid daughter cells are formed. Each having half chromosome number as the original parent cell.