Meiosis

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Meiosis

• Forming haploid cells for sexual reproduction

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(No Transcript)
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Interphase
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Prophase
Crossing Over
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Prophase 1

• Chromosomes ____________.
• Nuclear membrane ___________.
• Centrioles move and spindles form

condense
disappears
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Prophase 1 cont.

• _________ occurs pairing of homologous
  chromosomes (pair of the same type of chromosome
  but one from each parent)
• Forms a ______ 4 sister chromatids
• _____________ occurs portions of chromatids may
  break off and reattach on adjacent chromatids

Synapsis
tetrad
Crossing-over
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Crossing over
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Metaphase and Anaphase
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Metaphase 1 and Anaphase 1

• Homologous pairs line up at the equator
• Spindle fibers attach to the _____________ of
  each homologous pair
• Homologous pairs split and move to _______ _____

centromere
opposite poles
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Telophase and Cytokinesis
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Telophase 1
Chromosomes

• _____________reach opposite poles of the cell
• ___________ occurs the cell divides.
• The resulting cells are ______, (n).

Cytokinesis
haploid
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Prophase 2
sister chromatids

• Centromeres of _____ ________ attach to spindle
  fibers.
• Nuclear membrane__________.

disappears
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Prophase 2

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Metaphase 2
Sister chromatids

• _____ __________ line up on the equator

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Metaphase 2

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Anaphase 2

• Chromatids separate and move to _______ ______ of
  the cell.

opposite poles
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Anaphase 2

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Telophase 2
Nuclear membrane

• ______ __________ forms around the chromosomes.
• The cells divide by _________.
• The resulting 4 cells are ________, (n).
• These reproductive cells are called _______.

cytokinesis
haploid
gametes
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Telophase and Cytokinesis

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Meiosis

• The process of nuclear division that produces
  haploid cells with half the number of chromosomes
  as the original diploid cell.

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Why have meiosis?

• Results in genetic variation in the new
  offspring.

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Diagram of Meiosis
Diploid cell (2n)
Haploid cell (n)
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More sources of genetic variation

• Crossing-over
• In prophase 1, when homologous chromosomes
  exchange genetic information
• Random fertilization
• A sperm and egg unite, forming a zygote.

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What are germ cells

• Only germ cells undergo meiosis to produce
  haploid reproductive cells.

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What are somatic cells?

• All other cells in the body are somatic cells.
  Normally diploid.

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Gamete development

• Gametes are only formed in specialized
  reproductive organs in an organism.
• Spermatogenesis formation of sperm cells.

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• Oogenesis formation of egg cells. A parent
  cell produces only 1 mature egg, which receives
  most of the cytoplasm. The other 3 cells are
  called polar bodies and they degenerate.

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Lets Review

1. What are homologous chromosomes?
2. What happens to homologous pairs during metaphase
   1?
3. How many chromosomes are in a cell at the end of
   telophase 1?
4. How many chromosomes are in a cell at the end of
   telophase 2?