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Published byAndor Orbán Modified over 5 years ago
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Meiosis – a form of cell division that halves the number of chromosomes when forming reproductive cells, such as gametes (egg & sperm cells)
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Stages of Meiosis: *Before meiosis begins, DNA in
the original cell is replicated. In meiosis, the cell undergoes two cell divisions: Meiosis I and Meiosis II. The cell then goes through two cell divisions: Meiosis I and Meiosis II.
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Meiosis I: Meiosis I: Homologous chromosomes
separate; This stage consists of prophase I, metaphase I, anaphase I, and telophase I.
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Meiosis I 2n Crossing Over Independent Assortment n
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Crossing Over Occurs when portions of a chromatid on one homologous chromosome is broken and exchanged with the corresponding chromatid portion of the other homologous chromosome.
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Meiosis II: Meiosis II: The 2 chromatids (referred to
as sister chromatids) separate; This stage consists of prophase II, metaphase II, anaphase II, and telophase II.
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* All 4 cells are genetically different!!
Meiosis II n * All 4 cells are genetically different!! n
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2n Meiosis: -reduces the number of chromosomes by half to form gamete cells centromere n n
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Three Mechanisms that Contribute to Genetic Variation:
1. crossing over – when portions of a chromatid on one homologous chromosome is broken and exchanged with the corresponding chromatid portion of the other homologous chromosome 2. independent assortment – the random distribution of homologous chromosomes during meiosis 3. random fertilization – the random joining of 2 gametes
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Importance of Genetic Variation:
It allows organisms to change so they can better adapt to the changing environment !
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