Meiosis and Mutations

Remember:  Mitosis - takes place in regular body cells (somatic cells) and you end up with 2 identical diploid (2n) cells where “n” = the # of chromosomes.

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

Meiosis  Meiosis - takes place in sex cells (gametes) and you end up with four haploid (n) cells b/c there are 2 divisions (Meiosis I & II) –Female = egg –Male = sperm

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.

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

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)

 In males this meiosis is called spermatogenesis (“sperm creation”)  In females this meiosis is called oogenesis (“egg creation”)

Of the four cells produced in oogenesis, only one will develop into a fully functional egg. The other 3 lack the cytoplasm for development and are called polar bodies

 Sperm (n) from the male fertilizes Egg (n) from the female and a zygote (2n) is formed

 There is no new genetic information introduced in Mitosis –everything is identical  What about Meiosis? –YES, NEW genetic information is introduced! Genetic variation makes us all look different! –½ from mom & ½ from dad