Warm-Up 12/4/12 1. What phases of mitosis are seen here? A B C 2. What are chromosomes made of? 3. What is the difference between somatic and germ cells?

Mitosis Review What is it: involves.. Nuclear Division Where does it occur: different cells in body except for certain areas such as brain or nerve cells Function: Grow and repair tissues 4 Parts: prophase, metaphase, anaphase, telophase Produce: 2 identical cells w/ same number of chromosomes as parent cell in each new cell

Meiosis Overview What is it: Nuclear divisions to reproduce an entire organism. Where does it occur: Reproductive cells: Ovaries in females, Testes in males. Function: To form gametes (egg & sperm) 8 Parts: Meiosis I – prophase I, metaphase I, anaphase I, telophase I Meiosis II – prophase II, metaphase II, anaphase II, telophase II Produces: 4 cells with HALF the number of chromosomes as parent cell in each new cell.

Sexual reproduction Fusion of two gametes to produce a single zygote. Introduces greater genetic variation by allowing genetic recombination. With exception of self-fertilizing organisms, like some plants, a zygote receives gametes from two different parents.

Terms you should know: Examples: humans have 46 chromosomes Diploid (2n) - Normal amount of genetic material Haploid (n) - 1/2 the genetic material. Examples: humans have 46 chromosomes Mitosis = 46 chromosomes in daughter cells (diploid) Meiosis =23 chromosomes in each daughter cell (haploid)

Human egg = 23 chromosomes (Haploid) Human sperm = 23 chromosomes (Haploid) When egg is fertilized by sperm, the zygote now has 46 total chromosomes (diploid) Q: After Mitosis, are the two new daughter cells genetically identical? Q: After Meiosis, are the four new daughter cells genetically identical?

Interphase Sister chromatids During interphase, amount of DNA doubles 2 identical chromosomes 7

Meiosis I – Prophase I During prophase 1 homologous chromosomes stack up on top of each other. Chromosomes often exchange parts and become recombined. This process, called “Crossing Over,” increases genetic variety of resulting gametes!

Crossing over Crossing over produces recombinant chromosomes. Meiosis KM

Chromosomes after crossing over Meiosis KM

Meiosis I – Metaphase I The chromosomes line-up in the middle of the cell. They’re arranged randomly (independent assortment)

Independent assortment Meiosis KM

Meiosis I – Anaphase I The chromosomes are separated, pulling homologous chromosome pairs to opposite ends of the cell. Homologous Chromosomes

Telophase I & Cytokinesis The cell separates! Q: Are the two cells genetically identical? Q: What has caused their differences?

Meiosis II – Prophase II & Metaphase II Centrioles migrate to the poles again to prepare for a second division. Sister chromatids line up in the middle. Again, randomly arranged along the equator. (Ind.Assrtmnt) Sister Chromatids

Meiosis II – Anaphase II Sister chromatids separates from each other.

Meiosis II – Telophase II & Cytokinesis Nuclear envelope and nucleolus appear 4 Haploid cells are created Notice the variety they all have! Q: How can each of the haploid cells become diploid again?

Meiosis KM

Meiosis KM

Let’s See it all together http://www.classzone.com/cz/books/bio_07/resources/htmls/animated_biology/unit3/bio_ch06_0175_ab_meiosis.html

What happens when a fertilized gamete has too many or too few chromosomes? Non-disjunction When an abnormal separation occurs during meiosis I or meiosis II. The gametes will either have too few or too many chromosomes.

Conditions caused by non-disjunction In humans, non-disjunction may lead to one of many serious medical conditions such as.. Down syndrome (trisomy 21) Turner Syndrome (lack of X) Klinefelter Syndrome (XXY) Teenaged girls with Down syndrome

Just how much genetic variety? 23 chromosomes in haploid cells… 2n = 223 = _____ possible combination person? 8.3 mil.

Random Fertilization also increases variety At least __________ combinations from Mom, and another ____________ from Dad … _________ combinations for a diploid zygote!!! 8.3 million 8.3 million 70.3 trillion

What does this mean for us? Chromosomes have genes that code for proteins that give us traits. For example, hair is made of protein and depending on your genetics, your hair is made of a specific protein that causes your hair to be curly, wavy, or straight. Some traits are expressed more strongly than others. These are called dominant traits. The weaker traits are said to be recessive.