Chapter 12

BiologySixth Edition

Raven/Johnson

(c) The McGraw-Hill Companies, Inc.

The purpose of meiosis is to produce haploid (n) cells from diploid (2n) cells.

Each haploid cell has only 1 type of each chromosome.

2N

Male

Female

2N

Meiosis

Meiosis has an end point, unlike mitosis which is a cycle.

Meiosis has two periods and consists of two cellular divisions.

Phases of Meiosis:

Prophase I; Metaphase I; Anaphase I; Telophase I

Interkinesis

Prophase II; Metaphase II; Anaphase II; Telophase II

You need to know what is happening to the chromosomes at each of these phase!!

Meiosis I – separates homologous chromosomes

Meiosis II – separates sister chromatids.

Important meiotic events you need to know:

Synapsis; Crossing Over; Random Orientation

Prophase I Metaphase I

Homologous chromosomes pair all along their length.

Physical pieces of homologous chromosomes change chromosomes.

‘although you get you fathers copy of chromosome #1, chances are some of that chromosome contains some of your mothers genetic material’

Mother Father

Chiasma – X shapes formed when homologous chromosomes are crossing over.

Homologous Chromosomes

Because Chiasmata hold homologues together, microtubules only fuse to one side of the kinetochore.

Microtubules fuse to both sides of the kinetochore during mitosis.

The End.