Intro to Meiosis

What is it?

Who does it?

Where does it happen?

Why does it happen?

Why is a different process needed?

MeiosisMaking sex cells (sperm & eggs)

All sexually reproducing organisms

To allow organisms to reproduce

1) Chromosome # needs to be cut in half2) Creates genetic diversity (can help evolution of species)

In males- in the testesIn females- in the ovaries

Diploid adult MITOSIS FERTILIZATION

MEIOSIS

Haploidgametes

Diploidzygote

Meiosis allows sex cells to join to form a completeset of chromosomes/instructions to make a new organism.

Remember, humans have 23 pairs of chromosomes

Pairs 1-22 are said to beHomologous chromosomes(they go together becausethey have same traits but arenot identical)

Gene for eye color

Gene for hair color

Now let’s look at how sex cells are made…

Eight Stages of Meiosis1)Prophase I2)Metaphase I3)Anaphase I4)Telophase I

5)Prophase II6)Metaphase II7)Anaphase II8)Telophase II

Prophase I: Crossing over occurs between replicated homologous chromosomes

Crossing over(exchanging parts)

Note: chromosomes indaughter cells are all different

Note: “X’s” are next to each other, not above each other

Metaphase I: Replicated chromosomes get next to each other in the cell

Anaphase I: homologous chromosomes separate

Telophase I: replicated chromosomes still need to be separated

still looks like an “X”

Now Meiosis II occurs (looks like mitosis)

Meiosis

Meiosis animation

Meiosis technical

And now let’s see a more technical version…

One final detail…

The End!