Table of contents• Intro to Bio Notes Page #• Types of Biology Activity Page # • Body System Notes Page # food

Journal (3 pages)Page #- Page #• Digestion Notes Page #• Biomolecules Notes Page #• Cardio Vascular Notes Page #• Daphnia Lab- Data and procedures

Page #• Doing Science Notes Page #• Meiosis Notes Page #

Meiosishttp://www.youtube.com/watch?

v=35ncSrJOwME&feature=related

The Standards• 2a: Meiosis is an early step in

sexual reproduction in which the pairs of chromosomes separate and segregate randomly during cell division to produce gametes containing one chromosome of each type.

• b. Students know only certain cells in a multicellular organism undergo meiosis.

• Meiosis: Process of cell division that makes gametes (sex cells)• 2 cell divisions

• (Meiosis 1, then Meiosis 2)• Makes haploid cells

Human sperm cells Human egg (ovum) cell

• Gamete: Sex cells–Male = sperm–Female = ova/egg

• Fertilization: Union of male and female gametes

• Zygote: Diploid cell that results from the fusion of two haploid gametes

• Homologous Chromosomes: chromosomes that are the same size, shape, and carry the same traits.

• Diploid: two identical copies of every chromosome. (ALL somatic (body) cells)– Human diploid # = 46

• Haploid: one copy of every chromosome. (ONLY sex cells)– Human haploid # = 23

Diploid Haploid

• Mitosis starts with 1 diploid cells, then makes 2 identical diploid cells.

• Meiosis starts with 1 diploid cell, then makes 4 unique haploid cells.

Between Mitosis and Meiosis:

• Prophase 1 – • Crossing-over

happens.

Tetrad

Mom Dad

synapsis

• Crossing over: parts of homologous pairs break off and re-form on the adjacent chromosome

Homologous pair in tetrad formation

* Notice: chromosomes are aligned so the genes on one match corresponding genes on the other.

•Metaphase 1 – homologous pairs line up in the middle of the cell

•Anaphase 1 – homologous pairs split apart from each other• Independent assortment happens

• Independent assortment: Chromosomes separate from each other randomly.

FYI:• The more chromosomes, the more ways they can line up…leading to more genetic diversity

• Humans have 23 sets of chromosomes, so lots of combinations are possible.

• Telophase 1 – We end up with 2 haploid cells.These cells enter Meiosis 2

•These cells are not finished yet!!! Time for

Meiosis 2!

• Looks exactly like mitosis - consists of Prophase 2, Metaphase 2, Anaphase 2, Telophase 2

• Occurs in each cell from meiosis 1, this results in four new daughter cells

• The new cells will develop into sperm or eggs

• Now you can fill out the major events for meiosis 2 on your chart by looking at the major events in mitosis!

Meiosis Overview

DNA is doubled

Meiosis I: homologous pairs separate

Meiosis II: sister chromatids

separate

2n

n

n

Meiosis:• 2n 1n• Cells divide

twice• 1 cell 4 cells• Happens in sex

cells

Mitosis vs. MeiosisMitosis:• 2n 2n• Cells divide

once• 1 cell 2 cells• Happens in

non-sex cells

Summary1. One major way that meiosis is

different from mitosis is…

2. The major events of Prophase 1 are…

3. The major events of Anaphase 1 are…

4. Variation is caused by…