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MEIOSIS

MEIOSIS. REVIEW SUPPLEMENTARY INFORMATTION: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeiosis.html. Sexual reproduction occurs only in eukaryotes. Meiosis – produces gametes In gametes the number of chromosomes is reduced by half

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MEIOSIS

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  1. MEIOSIS REVIEW SUPPLEMENTARY INFORMATTION: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeiosis.html

  2. Sexual reproduction occurs only in eukaryotes. • Meiosis – produces gametes • In gametes the number of chromosomes is reduced by half • The full amount of chromosomes when the two gametes fuse during fertilization.

  3. Meiosis is a special type of nuclear division which segregates one copy of each homologous chromosome into each new "gamete" • Homologues (homologous chromosomes) • A pair of chromosomes • one member of the pair is obtained from the organism's maternal parent and the other from the paternal parent; • found in diploid cells

  4. Two successive nuclear divisions occur Meiosis I (Reduction) and Meiosis II (Division) • Prophase I • has a unique event -- the pairing (by an as yet undiscovered mechanism) of homologous chromosomes • Synapsis is the process of linking of the replicated homologous chromosomes. • The resulting chromosome is termed a tetrad, being composed of two chromatids from each chromosome, forming a thick (4-strand) structure

  5. Tetrad

  6. Tetrad • The alleles on this tetrad: • A B C D E F G • A B C D E F G • a b c d e f g • a b c d e f g

  7. Crossing Over

  8. A B C D E F GA B c d e f ga b C D E F Ga b c d e f g • Instead of producing only two types of chromosome (all capital or all lower case), four different chromosomes are produced. • This doubles the variability of gamete genotypes. • Crossing-over is indicated by a special structure, a chiasma (plural chiasmata)

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