1. MEIOSIS  In sexually reproducing organisms, gametes (sex cells) are produced by a special type of cell division called meiosis.  Meiosis results in gametes with the half number of chromosomes as the parent cell.

2.  Somatic cells, or body cells has a certain number of chromosomes. For ex: Human somatic cells have 46 chromosomes.  In humans, these 46 chromosomes can be arranged into 23 pairs.  The chromosomes that make up each pair are called homolgous chromosomes. Diploid and Haploid Chromosome Numbers

3.  Homologous chromosomes are similar in size and shape, and they have similar genetic content. (In humans the sex chromosomes are not homologous in males.)  The cells that have all the homologous chromosomes are diploid, or 2n. Diploid and Haploid Chromosome Numbers  Unlike the body cells, gametes do not contain pairs of homologous chromosomes. They have only one chromosome from each pair and are called haploid, or n.

7. Crossing-over

8. COMPARISON OF MITOSIS AND MEIOSIS MITOSISMEIOSIS Used in asexual reproduction; growth, development and repair in multicellular organisms Used in sexual reproduction Occurs in the body (somatic) cells. The cells may be diploid (2n) or haploid (n) Occurs during gamete formation of organisms that show alternation of generation (metagenesis) Occurs in the diploid primary sex cells of sexually reproducing organisms. Produces gametes in animals, spores in plants and in some simple organisms Occurs throughout lifeOccurs only during reproductive ages Involves one cell divisionInvolves two cell divisions Two daughter cells are formedFour daughter cells are formed

9. COMPARISON OF MITOSIS AND MEIOSIS MITOSISMEIOSIS Synapsis of homologous chromosomes, tetrad formation and crossing over do not occur These events occur during Prophase I Sister chromatids seperate during anaphase Homologous chromosomes seperate during Anaphase I leading to reduction of chromosome number. Sister chromatids seperate during Anaphase II Maintains genetic (hereditary) continuity Leads to genetic variations. Increases the rate of evolution

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