Intro to Meiosis

What is it? Who does it? Where does it happen? Why does it happen? Why is a different process needed? Meiosis Making sex cells (sperm & eggs) All sexually reproducing organisms To allow organisms to reproduce 1)Chromosome # needs to be cut in half 2)Creates genetic diversity (can help evolution of species) In males- in the testes In females- in the ovaries

Diploid adult MITOSIS FERTILIZATION MEIOSIS Haploid gametes Diploid zygote Meiosis allows sex cells to join to form a complete set of chromosomes/instructions to make a new organism.

Remember, humans have 23 pairs of chromosomes Pairs 1-22 are said to be Homologous chromosomes (they go together because they have same traits but are not identical) Gene for eye color Gene for hair color

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

Eight Stages of Meiosis 1)P rophase I 2)M etaphase I 3)A naphase I 4)T elophase I 5)P rophase II 6)M etaphase II 7)A naphase II 8)T elophase II

Prophase I: Crossing over occurs between replicated homologous chromosomes Crossing over (exchanging parts)

Note: chromosomes in daughter 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!