Reduction-Division

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MEIOSIS

Reduction-Division

Genetic Recombination

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Meiosis

The form of cell division by which GAMETES, with HALF the number of CHROMOSOMES, are produced.

DIPLOID (2n)  HAPLOID (n)

Meiosis is SEXUAL reproduction.

TWO divisions (MEIOSIS I and MEIOSIS II).

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Meiosis

Sex cells divide to produce GAMETES (sperm or egg).

Gametes have HALF the # of chromosomes.

Occurs only in GONADS (testes or ovaries).

Male: SPERMATOGENESIS -sperm

Female: OOGENESIS - egg or ova

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Spermatogenesis

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Oogenesis

Polar Bodies (die)

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Interphase I

Similar to mitosis interphase.

CHROMOSOMES (DNA) replicate in the S phase

Each duplicated chromosome consist of two identical SISTER CHROMATIDS attached at their CENTROMERES.

CENTRIOLE pairs also replicate.

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Interphase I

Nucleus and nucleolus visible.

Nucleus

nucleolus

cell membrane

chromatin

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Meiosis I (four phases)

Cell division that reduces the chromosome number by one-half.

Four phases:

a. Prophase I

b. Metaphase I

c. Anaphase I

d. Telophase I

Prophase I

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Prophase I

Longest and most complex phase (90%).

Chromosomes condense.

Synapsis occurs - Homologous chromosomes come together to form a tetrad.

Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids).

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Non-Sister Chromatids-HOMOLOGS

Homologs contain DNA that codes for the same genes , but different versions of those genes

Genes occur at the same loci

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Prophase I - Synapsis

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Homologous Chromosomes

Pair of chromosomes (maternal and paternal) that are similar in shape and size.

Homologous pairs (tetrads) carry GENES controlling the SAME inherited traits.