THE FORMATION OF SEX CELLS MEIOSIS THE FORMATION OF SEX CELLS

What is the Purpose? Meiosis is similar to Mitosis in that cells are dividing. However, in Meiosis the overall result is different from mitosis. What was the overall result of Mitosis?

Mitosis Mitosis resulted in two identical daughter cells. Meiosis results in four completely different cells.

MEIOSIS is… The process in which a cell divides in order to produce gametes. Gametes = sex cells like sperm and eggs

Haploid Vs Diploid Mitosis results in 2 diploid cells. Diploid means a full set of chromosomes Meiosis results in 4 haploid cells. Haploid means only one half of the total chromosome number.

Original Cell has 4 chromosomes Sex Cells have 2 chromosomes (1/2 the number!)

How does this occur? Meiosis is actually a process in which the cell divides two times. The first division creates cells with the normal number of chromosomes (diploid). The second division creates cells with half the normal number of chromosomes (haploid)

Meiosis has 2 Divisions Meiosis II Meiosis I Products * Called the Reduction Phase * It Reduces the # of chromosomes in half Products Meiosis II Diploid Cells Haploid Cells

The Goal: A New Life Each of your cells undergo mitosis to produce exact copies of the original cell. But what about the first cell that was you? That cell was a combination of cells from both of your parents.

Importance of Meiosis Meiosis is important because it creates cells that are only half of what a “normal” cell would be. Haploid + Haploid = Diploid Egg + Sperm = Baby This way- when they meet up a “whole” cell is created a zygote (fertilized egg)

EGGS AND SPERM!!!!

Meiosis Each sperm and each egg were formed by the process of meiosis, Cells are created with only half of what they need to survive alone. Half the number of chromosomes!!

The First Division The first division is actually an extremely important division. This is when CROSSING OVER occurs

CROSSING OVER Traits switch chromosomal locations during CROSSING OVER A recombination of genes This happens at the beginning of Meiosis I, during Prophase I

10. Crossing Over Why is crossing over important? Results in new combinations of genetic info “Shuffles the deck of genetic cards” Provide variation This is why you are different from your parents and siblings

Then What?? After crossing over, which occurs during Prophase I, the cell undergoes Metaphse, Anaphase and Telophase…. Then it divides again, resulting in…

CELLS WITH ONLY HALF THE NUMBER OF CHROMOSOMES!!!!!!!!!!!!

Phases of Meiosis I Interphase I Prophase I Metaphase I Anaphase I Telophase I – DNA replicates – Chromosomes appear and crossing over occurs! – Chromosomes line up – Chromosomes pulled apart – Cells divide

Phases of Meiosis II – Products of Meiosis I prepare to replicate again – Chromosomes line up – Chromosomes pulled apart – Cells divide into 4 GAMETES Prophase II Metaphase II Anaphase II Telophase II