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Notes E 4.3. Meiosis is a special form of cell division. Meiosis is necessary for sexual reproduction. Organisms that reproduce sexually produce gametes , sex cells that contain ½ as many chromosomes as body cells. Eggs —female gametes Sperm —male gametes

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notes e 4 3

Notes E 4.3

Meiosis is a special form of cell division.

meiosis is necessary for sexual reproduction
Meiosis is necessary for sexual reproduction.

Organisms that reproduce sexually produce gametes, sex cells that contain ½ as many chromosomes as body cells.

  • Eggs—female gametes
  • Sperm—male gametes
  • 1n—gametes, also called haploid cells, produced by the process of meiosis
slide3

In fertilization, 2 gametes join. The resulting cell is 2n, or diploid. I has pairs of chromosomes, with a homolog from each parent.

1n+1n=2n

cells divide twice during meiosis
Cells divide twice during meiosis.

Before meiosis, the DNA in each homolog is copied . The copies are referred to as chromatids and held together by a centromere. Meiosis differs from mitosis because:

  • The genetic material is divided not once, but twice
  • Four 1n (haploid) daughter cells are formed.

In meiosis I, the first 2 daughter cells are produced. They receive one of the homologs.

slide5

In meiosis II, these 2 daughter cells divide again, splitting the homolog so that each cell gets one of the copies.

Each of the 4 resulting daughter cells has half the number of chromosomes needed for offspring.

meiosis and mitosis differ in important ways
Meiosis and mitosis differ in important ways.
  • Cells that become gametes go through meiosis; all other cells divide by mitosis.
  • In meiosis, DNA is copied; then the cells divide twice.
  • Each cell has only one homolog from one parent.
  • In mitosis, DNA is copied, and the cells divide just once. Each cell has 2 homologs, one from each parent.
slide7

Meiosis produces haploid (1n) daughter cells that have half of the genetic material of the parents.

  • Mitosis produces diploid (2n) daughter cells that have the same genetic material as the parents.
slide8

Meiosis produces gametes, cells specialized for reproduction.

  • During fertilization, 2 gametes combine and 2 haploid cells form into one diploid cells.
  • The cell then divides by mitosis, developing into a multicellular organism.