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Meiosis

PREPARED BY: SHERYL S. BAUTISTA

S8LT - IVd -

• Compare mitosis and meiosis, and their role in the cell -division cycle

Chromosomes and Chromosome Number Meiosis – Homologous Chromosomes  (^) Same length  (^) Same centromere position  Carry genes that control the same inherited traits  (^) One is from mother, one is from father = a matching set

Haploid and Diploid Cells  (^) Human gametes contain 23 chromosomes.  (^) A cell with n chromosomes is called a haploid cell.  (^) A cell that contains 2 n chromosomes is called a diploid cell. Meiosis  (^) An organism produces gametes to maintain the same number of chromosomes from generation to generation.

Meiosis I Meiosis  Interphase  (^) Chromosomes replicate.  (^) Chromatin condenses. Interphase

Meiosis I Meiosis  Prophase I  Pairing of homologous chromosomes occurs.  (^) Each chromosome consists of two chromatids.  (^) The nuclear membrane breaks down.  (^) Spindles form. Prophase I

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

Meiosis I Meiosis  Anaphase I Anaphase I  (^) Homologous chromosomes separate and move to opposite poles of the cell.

Meiosis II  (^) Prophase II Meiosis  (^) A second set of phases begins as the spindle apparatus forms and the chromosomes condense. Prophase II

Meiosis II  (^) Metaphase II Meiosis  (^) A haploid number of chromosomes line up at the equator. Metaphase II

Meiosis Meiosis II  (^) Telophase II  The chromosomes reach the poles, and the nuclear membrane and nuclei reform. Telophase II

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

Meiosis Provides Variation  (^) Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result.  (^) Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine. Meiosis

Mitosis vs Meiosis