Sexual Reproduction

Sexual Reproduction - makes it possible to maintain a...

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Sexual Reproduction: Meiosis A second type of cell division called  meiosis  takes place in multicellular eukaryotes. This is a  reduction division  in which the daughter cells receive exactly half the number of chromosomes of  the mother cells.  Meiosis occurs in the production of  gametes —the  sperm  of the males and the  eggs  of the females.  When a sperm fertilizes an egg, a  zygote  is produced with the appropriate number of chromosomes  for the species—in humans (and potatoes) the zygote and the somatic (body) cells produced from it  have 46 chromosomes. This is the  diploid  (2  n ) number of chromosomes, half of which have come  from the sperm nucleus, half from the egg. The sperm and egg are  haploid  (  n ); they carry half the  number of chromosomes of the body cells (in humans, 23 in each sperm and egg). Meiosis thus 
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Unformatted text preview: makes it possible to maintain a constant number of chromosomes in a species that reproduces sexually by halving the number of chromosomes in the reproductive cells. Meiosis uses many of the same mechanisms as mitosis and is assumed to have been derived from mitosis after the latter procedures were in place in some early organisms millenia ago. Figure 1 shows the stages of mitosis, and Figure 2 shows the stages of meiosis. Note that the names for the stages are the same as those of mitosis, with the addition of a numeral to designate either the first or the second divisional stage. Both divisions are part of meiosis; not until the final four daughter cells are produced is the process complete....
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This note was uploaded on 11/14/2011 for the course BIO 1421 taught by Professor Farr during the Fall '08 term at Texas State.

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