Meiosis 10/29/09

What can you tell me about Mitosis?

Let’s Review! Interphase Prophase Metaphase Anaphase Telophase & Cytokinesis

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Two main cell types in your body! 1. Diploid Somatic cells (body cells) Have 23 pairs of homologous chromosomes 2. Haploid Reproductive (sex) cells Sperm and egg cells Also called gametes Only contain 23 chromosomes (not paired!!)

Meiosis Meiosis is the type of cell division by which gametes (eggs and sperm) are produced. One parent cell produces four daughter cells. During meiosis, DNA replicates once, but the nucleus divides twice.

Meiosis I 1 st division of meiosis

Prophase 1: Each chromosome duplicates and remains closely associated. These are called sister chromatids. Crossing over – portions of the sister chromatids exchange spots.

Crossover a. The process by which two chromosomes pair up and exchange sections of their DNA. Each chromosome is from one parent b. This process leads to offspring having different combinations of genes from their parents

Metaphase I Chromosomes align at the center of the cell.

Anaphase 1: Chromosome pairs separate with sister chromatids remaining together.

Telophase I Two daughter cells are formed with each daughter containing only one chromosome of the chromosome pair.

Meiosis II 2 nd Stage of meiosis

Prophase 2: DNA does not replicate.

Metaphase 2: Chromosomes line up at the center of the cell

Anaphase 2: Centromeres divide and sister chromatids move separately to each pole.

Telophase 2: Cell division is complete. Four haploid daughter cells are formed

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Meiosis

Differences in Mitosis & Meiosis Mitosis Asexual Cell divides once Two diploid daughter cells Genetic information is identical Makes somatic cells – body cells 2n Meiosis Sexual Cell divides twice Four haploid daughter cells Genetic information is different Makes gametes – sex cells n