Meiosis

Mitosis is for… Growth, development, & repair Somatic cells (all cells except reproductive ones)

Mitosis results in… 2 daughter cells Exact copies of the parent cell Diploid (has a complete set of DNA)

Meiosis is for… Creating reproductive cells—sperm & eggs We call these cells gametic cells (or gametes)

First we need to understand a little about the human chromosomes! Humans have 46 chromosomes Half the set (23 chromosomes) comes from the mother; the other half comes from the father Chromosomes carry genes—units of information that code for proteins Each parent gives half of his or her genes to the offspring The two chromosomes in each pair are called homologous chromosomes The two chromosomes of each pair carry genes for the same traits (ex: eye color) at the same location However, this is not necessarily the same form of that gene (brown vs. blue eyes)

Here is a look at our chromosomes

Meiosis results in… 4 haploid cells Haploid=half the DNA of the parent cell When a sperm and egg come together to create a baby, they are both contributing half of the DNA to create a baby with a full set of DNA What would happen if sperm & egg were diploid (had a full set of DNA)?

Overview of Meiosis

Meiosis is two phases Remember cells go through interphase Then Meiosis begins! Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Prophase 2 Metaphase 2 Anaphase 2

Prophase 1 Chromosomes are condensed. Sister chromatids are present. The homologous chromosomes pair up. This part does not take place in mitosis!!!

Metaphase 1 Homologous chromosomes line up along the middle of the spindle fibers (called the equator)

Anaphase 1 Homologous chromosomes move to opposite ends of the cell

Telophase 1 The parent cell divides into two cells. The cells can have any combination of maternal and paternal chromosomes!!! These two cells will now enter the second phase of meiosis.

Prophase 2 The cell is now two cells. The second phase of meiosis is very similar to mitosis!

Metaphase 2 Sister chromatids now line up along the equator as in mitosis

Anaphase 2 The sister chromatids divide and move to opposite sides of the cell, just as we saw during mitosis.

Telophase 2 & Cytokinesis The cells completely divide to form four cells. Each cell has a half set of DNA. We call these cells haploid.

Animated Meiosis http://www.sumanasinc.com/webcontent/ animations/content/meiosis.html

Lets look at a cell with 4 chromosomes! We will now work together to draw out the progression of DNA during meiosis. What will be the end products? 4 cells, each with half the number of chromosomes (2)