6.1 MEIOSIS(Sexual Reproduction)Name:

Date:

Block:

Let’s Review:

  1. Mitosis occurs in somatic cells (body cells)
  2. E.g. When your body needs to grow, or cells eventually die
  3. One cell becomes two cells.
  4. These two cells are identical
  5. This can occur in single-celled organisms (bacteria) and this is how

they reproduce.

  1. Two identical cells form, (both with the same number of chromosomes.)
  2. In humans, 46 chromosomes (23pairs), we call this diploid (2n)

(Video: Recap Mitosis )

What is Sexual Reproduction?

  • TWO parents that produces offspring that are genetically DIFFERENT from each other
  • From either parent, and from any other member of their species.

What is the role does sexual reproduction play?

  1. To produce offspring (natural selection)
  2. Maintain genetic diversity
  3. This variation produces individuals that have advantages over one another

What is Meiosis?

  • Very specialized cell division that produces gametes
  • sperm for men and eggs for women

Video: Expiation of Meiosis (and mitosis).

What is the purpose of Meiosis?

  • To reduce a normal diploid cell (2 copies of each chromosome per cell) to haploid cells, called gametes (1 copy of chromosome per cell)
  • In humans, haploid cells resulting from meiosis are eggs (female) or sperm (male)

How many divisions does Meiosis undertake?

  • Involves, not one, but TWO cell divisions
  • Meiosis I and Meiosis II

Meiosis I

  • A pair of matching chromosomes called homologous chromosomes, one from each parent, separate and move to opposite poles of the cell
  • (sister chromatids still attached)
  • 2 daughter cells result from Meiosis I

Meiosis II

  • DNA is not replicated again before meiosis II begins.
  • Meiosis II is like mitosis; the sister chromatids separate to opposite poles of the cell resulting in each daughter cell inheriting one chromatid from each chromosome.
  • The end result is 4 haploid cells, each with ½ the number of chromosomes.
  • These develop into gametes

Video: Ever wonder why children do not look exactly like their parents?

This video explains genetic diversity and Meiosis (I and II).

How does variation (genetic diversity) occur within this process?

  1. Crossing Over (Meiosis I)
  2. Non-sister chromatids exchange DNA segments
  3. Each chromosome picks up a new genetic information from each other
  4. What is the purpose of this?
  5. This increases the genetic possibilities and produces more variation within a population
  1. Independent Assortment (Meiosis I)
  2. Homologous pairs of chromosomes separate and sort themselves
  • Homologous pairs of chromosomes line up at the equator and separate independently to opposite poles
  • How does this result in the shuffling of genes that contribute to variation and genetic diversity?

Checking your Understanding:

1. What does the term genetic diversity mean?

______

2. What is the function of meiosis?

______

3. (a) What is the haploid number of chromosomes in humans? ______

(b) What is the diploid number of chromosomes in humans? ______

Do men and women produce the same number of gametes (or sex cells)? ______

What are Gametes and how do they form?

In males:

  • End of Meiosis II - produce 4spermcells.
  • ALL4 cells may develop into mature sperm.

In females:

  • End of Meiosis II – produce 1 egg cell
  • WHY? Unequal division of cytoplasm and organelles in Meiosis I.
  • End of Meiosis II, 1 cell gets most of the cytoplasm and becomes the egg (other 3 disintegrate).

Can you put the photo (above) into your own words?

______

Let’s Review: Mitosis and Meiosis

In your own words, explain what occurs during:

  1. Mitosis

______

  1. Meiosis:

______