By: Aya El-Ghajiji

IFY

Meiosis

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

ChromosomeChromatinChromatidSister chromatidsHomologous pair

ChromosomeStructure of DNA in nucleus

providing genetic information.

chromatinThe material of which

chromosomes are made = DNA + histone proteins.

Chromatid Chromosome copy. One pair of

replicated chromosomes found during Interphase.

Sister chromatidsIdentical copies of one

chromosome.

Homologous pairPair 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 ahaploid cell.A cell that contains 2n chromosomes is

called adiploid cell.

Meiosis

Interphase◦Chromosomes replicate◦Centriole pair replicates.

Meiosis I

Interphase

Meiosis I

Prophase I◦Chromatin condense◦Pairing of homologous chromosomes

◦Each chromosome consists of two chromatids.

◦The nuclear membrane breaks down.

◦Spindles form.

Meiosis IProphase I

◦Crossing over produces exchange of genetic information.

◦Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.

Meiosis IMetaphase I

◦Homologous chromosomes line up at the equator.

◦Chromosome centromeres attach to spindle fibers.

Meiosis IAnaphase IHomologous chromosomes separate and move to opposite poles of the cell.

Meiosis ITelophase I

◦The spindles break down.◦The cell divides.◦Cytokinesis

Meiosis IIProphase II

◦Spindle apparatus forms◦chromosomes condense.

Meiosis IIMetaphase II

◦A haploid number of chromosomes line up at the equator.

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

Meiosis IITelophase II

◦The chromosomes reach the poles, and the nuclear membrane and nuclei reform.

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

The Importance Of Meiosis

It results in genetic variation

Meiosis

http://www.youtube.com/watch?v=kVMb4Js99tA 

QuizA human cell containing 22

autosomes and a Y chromosome is ◦A zygote◦A sperm cell◦An ovum

QuizHomologous 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.