Meiosis By: Aya El-Ghajiji IFY

Meiosis Human body cells have 46 chromosomes. Each parent contributes 23 chromosomes. It produces sex cells (gametes): egg and sperm. One cell becomes 4 NON-IDENTICLE cells

Genetic Terms Chromosome Chromatin Chromatid Sister chromatids Homologous pair

Chromosome Structure of DNA in nucleus providing genetic information.

chromatin The material of which chromosomes are made = DNA + histone proteins.

Chromatid Chromosome copy. One pair of replicated chromosomes found during Interphase.

Sister chromatids Identical copies of one chromosome.

Homologous pair Pair of chromosome each coding for the same characteristics originally from the male parent and one from the female parent.

WHY DO WE NEED MIOSIS? To maintain the same number of chromosomes from generation to generation. Human gametes contain 23 chromosomes. A cell with n chromosomes is called a haploid cell. A cell that contains 2n chromosomes is called a diploid cell.

Meiosis

Meiosis I Interphase Chromosomes replicate Centriole pair replicates.

Meiosis I Prophase I Chromatin condense Pairing of homologous chromosomes Each chromosome consists of two chromatids. The nuclear membrane breaks down. Spindles form.

Meiosis I Prophase I Crossing over produces exchange of genetic information. Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.

Meiosis I Metaphase I Homologous chromosomes line up at the equator. Chromosome centromeres attach to spindle fibers.

Meiosis I Anaphase I Homologous chromosomes separate and move to opposite poles of the cell.

Meiosis I Telophase I The spindles break down. The cell divides. Cytokinesis

Meiosis II Prophase II Spindle apparatus forms chromosomes condense.

Meiosis II Metaphase II A haploid number of chromosomes line up at the equator.

Meiosis II Anaphase II The sister chromatids are pulled apart at the centromere by spindle fibers and move toward the opposite poles of the cell.

Meiosis II Telophase II The chromosomes reach the poles, and the nuclear membrane and nuclei reform.

Meiosis II Cytokinesis results in four haploid cells, each with n number of chromosomes.

The Importance Of Meiosis It results in genetic variation

http://www.youtube.com/watch?v=kVMb4Js 99tA Meiosis http://www.youtube.com/watch?v=kVMb4Js 99tA  

Quiz A human cell containing 22 autosomes and a Y chromosome is A zygote A sperm cell An ovum

Quiz Homologous chromosomes segregate toward opposite poles of a dividing cell during Mitosis Meiosis I Meiosis II

Bibliography BAKER, M., INDGE, B., & ROWLAND, M. (2001). Further studies in biology. London, Hodder & Stoughton. CAMPBELL, N. A. (1996). Biology. Menlo Park, Calif, Benjamin/Cummings Pub. Co. Llopis-Garcia, R., (2012) Meiosis Notes. City of Bath College. PARSONS, R. (2009). AS & A2 Biology: complte revision guide and practice : exam board AQA. Kirkby-in- Furness, Coordination Group. TOOLE, G., & TOOLE, S. (2008). AQA biology AS. Cheltenham, Nelson Thornes.