Meiosis Notes

  • The form of ______by which gametes, with
  • ______the number of chromosomes, are produced.
  • ______(2n) ______(n)
  • Involves two divisions:
  • ______
  • ______
  • Sex cells divide to produce gametes
  • ______or
  • ______
  • Gametes have ______the number of chromosomes.
  • Occurs only in gonads (testes or ovaries).
  • Processes:
  • Male: ______
  • -making of sperm
  • Female: ______
  • -making of eggs
  • Meiosis is similar to ______ with some chromosomal differences.

Copy the Spermatogenesis diagram here:

Stages:

  • Interphase I
  • Meiosis I
  • Interphase II
  • Meiosis II

Interphase I

  • Similar to ______ interphase.
  • DNA replicates in the
  • ______phase
  • Each duplicated chromosomewill eventually consist of two identical sister ______attached at their ______.
  • Nucleus and ______are visible.

Meiosis I (four phases)

  • prophase I
  • metaphase I
  • anaphase I
  • telophase I

Prophase I

  • Longest and most complex phase (90%).
  • ______come together to form a ______.
  • Tetrad is two chromosomes or four ______total.
  • One of the chromosomes comes from Mom and one from Dad

  • ______ condense.
  • ______ form.

Metaphase I

  • Shortest phase
  • ______align on the equator.
  • Chromosomes are lined up
  • with their ______

INDEPENDENT ASSORTMENT OCCURS:

  • Orientation of homologous pairs(to poles) is ______.
  • In the tetrad, Mom’s chromosome could be on the left or the right with

______’s on the other side.

  • Leads to Genetic Variation

  • Humans have ______chromosomes or
  • 23 ______of chromosomes.

Since each pair lines up randomly from every other pair, there are

8 million different combinations of the 23 pairs!!!

Anaphase I

  • ______chromosomes separate and move towards the poles.
  • Sister ______remain attached at their ______.

Telophase I

  • Each pole now has ______set of replicated chromosomes.
  • BUT the chromosomes still consist of two chromatids.

Meiosis II

  • Very short interphase II –
  • no moreDNA replication
  • The next set of cell divisions will separate the chromatids.
  • Meiosis II is similar to ______. Can you figure out how?

Meiosis II (four phases)

  • ______II
  • ______II
  • ______II
  • ______II

Prophase II

  • same as prophase in______
  • (Hint: you already know this picture! But now both cells go on together…)

Metaphase II

  • same as metaphase in ______
  • The chromosomes line up at the ______

Anaphase II

  • same as anaphase in ______

The chromatidsseparate at their______and move towards the opposite poles.

Telophase II

  • Same as telophase in mitosis.
  • Nuclei form.
  • Four haploid daughter cells produced.

The End Product of Meiosis

  • From one cell in the gonads (testes or ovary), 4 new cells will be formed.
  • Each of the new cells will contain only one member from each homologous pair.
  • Either the chromosome from Mom or Dad but NOT both!!!---Haploid!
  • Question:
  • A cell containing 20 chromosomes (diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?
  • 10 chromosomes (haploid): Just / by 2--- 20/2=10
  • Question:
  • A cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?
  • 10 chromosomes: First find the chromosome number from the chromatids:
  • 2 chromatids in a chromosome, so 40/2= 20 chromosomes.
  • 20/2= 10.