Meiosis Remember Mitosis Before a cell divides the

Meiosis

Remember Mitosis? • Before a cell divides, the number of chromosomes (the DNA) must double. • Then each new cell can receive the correct number of chromosomes (DNA).

MITOSIS • Mitosis is when the nucleus of the cell divides. one nucleus one cell identical nuclei identical DNA two nuclei two cells

MITOSIS Parent Cell DNA condenses into chromosomes Chromosomes align on the equator Chromosomes separate Two daughter cells

Mitosis

It’s all about chromosomes! • There are 46 chromosomes in human body cells • The number of chromosomes remain constant during Mitosis 46 46 46

What is Meiosis? • Meiosis is the formation of gametes (egg or sperm) with a haploid chromosome number, Fertilized Egg Cell

What is Meiosis? • The fertilized egg (zygote) produced by the sperm uniting with the egg then undergoes mitotic division to make the baby. Fertilized Egg Cell

Why Meiosis? • The gametes must have only half the necessary chromosome number for a species 23 • When two gametes unite, the resulting cell must have the exact chromosome number for that species. 23 46

Cell Differentiation Nerve Cells Muscle Cells Blood Cells Skin Cells Stem Cells • New individuals arise from zygote stem cells through cellular differentiation

Meiosis: In a nut shell…. • 4 daughter cells produced • Each daughter cell has half the chromosomes of the parent • 2 sets of cell division involved

Meiosis • Meiosis begins with a diploid parent cell • Meiosis ends with four haploid daughter cells

MEIOSIS Paternal Homologs • Meiosis has two divisions • Division 1, immediately followed by Division II Two Daughter Cells 2 nd Division of Mieosis 1 st Division of Meiosis Maternal Homologs Four Daughter Cells

Meiosis

Meiosis What differences can be seen with meiosis at this point?

Meiosis

Meiosis What differences can be seen with meiosis at this point?

Meiosis Diversity • Meiosis results in gamete cells unlike the parent cell. • Gamete cells have only half the chromosome number. • Each of the four gamete haploid cells have a different mix of chromosomes.

Meiosis Diversity • Additional diversity can occur because of crossing over. • Crossing causes parts of one chromosome to trade with another like chromosome. . • Certain traits “remix”.

Crossing Over • What is happening? a A b B c C a a A A b b B B c c C C a a A A b b B B c C c C • How does this affect the individual (offspring)? a b A B c C

Crossing Over • Click the link for a crossing over animation. • http: //www. tokyomed. ac. jp/genet/anm/mimov. gif

MEIOSIS – 6. Drawing • Meiosis has two divisions. • Meiosis results in four haploid cells unlike the parent cell.

Mitosis vs. Meiosis Event Mitosis Meiosis Produces 4 cells Produces 2 cells New cells identical New cells different New cells have the same number of chromosomes as parent New cells have fewer chromosomes than parent √ √ √

Mitosis vs. Meiosis Event Beginning cells diploid (2 n) Mitosis √ Meiosis √ Beginning cells haploid (n) Ending cells diploid (2 n) √ √ √ Ending cells haploid (n) Produces egg and sperm Produces body cells √