Do Now Please hand your homework in the bin. Then Answer in your notebooks: How do we get half of our DNA from each parent, and still only have 46 chromosomes?

Meiosis Chapter 10.1 and 11.3

Why does sex exist? Sexual reproduction creates genetic variability

Let’s Brainstorm… How do we get our different traits?

What is the difference between fraternal and identical twins?

Let’s define the following words… Meiosis: Sexual reproduction-production of gametes Gamete: Sex Cells (egg and sperm) haploid Somatic Cells: Body Cells - diploid

Haploid: Diploid: Fertilization: Zygote: Half the chromosome number (n) 1 of each pair of chromosomes (23) Diploid: 2 of each type of chromosome (2n) Twice the haploid number Fertilization: Sperm enters egg Zygote: Fertilized egg (diploid)

Chromosomes and Chromosome Number Human body cells have 46 chromosomes Each parent contributes 23 chromosomes Homologous chromosomes —one of two paired chromosomes, one from each parent

Homologous pair of chromosomes Centromere Figure 8.12 A homologous pair of chromosomes. This figure shows a pair of homologous chromosomes in their duplicated state. Each homologue is represented as a pair of chromatids. These two contexts for the word pair often confuse students. It would be helpful to introduce the term tetrad at this point, to emphasize both uses of the term pair. Sister chromatids One duplicated chromosome *

Homologous Chromosomes Same length Same centromere position Carry genes that control the same inherited traits

Karyotype

Meiosis The sexual life cycle in animals involves meiosis Meiosis produces gametes. When gametes combine in fertilization, the number of chromosomes is restored.

Cell Cycle Prepare Growth Division 2N 2N Mitosis Meiosis 2N N DNA Replication Prepare Growth Division 2N 2N Mitosis Meiosis 2N N

Do Now Label A, B, and C (Hint same size, same shape…)

Do Now Please put phones on my desk. Grab the worksheet, and a marker. Complete both sides No Notes, or partners. Yay BIO!! 

Meiosis 2 Divisions Meiosis I (separation of homologous chromosomes) Meiosis II (separation of sister chromatids)

Interphase Same as Mitosis (G1, S, G2) DNA- Chromatin Centrioles- located near the nucleus

Prophase I Pairing of homologous chromosomes occurs. (Synapsis) Each chromosome consists of two chromatids. The nuclear envelope breaks down. Spindles form

Prophase I (cont.) Crossing over produces exchange of genetic information. Crossing over —chromosomal segments are exchanged between a pair of homologous chromosomes.

Metaphase I Chromosome centromeres attach to spindle fibers Homologous chromosomes line up at the equator.

Anaphase I Homologous chromosomes separate and move to opposite poles

Telophase I/Cytokinesis The spindles break down. Chromosomes uncoil and form two nuclei. The cell divides into two haploid cells

Prophase II A second set of phases begins as the spindle apparatus forms and the chromosomes condense.

Metaphase II A haploid number of chromosomes line of at the equator Sister chromatids line up

Anaphase II The sister chromatids are pulled apart at the centromere by spindle fibers Move toward the opposite poles of the cell.

Telophase II The chromosomes reach the poles, and the nuclear membrane and nuclei reform.

Cytokinesis Cytokinesis results in four haploid cells Each with n number of chromosomes.

https://www.youtube.com/watch?v=rqPMp0U0HOA

Do Now Phones on my desk, and take out your homework. Then please grab the worksheet off my desk, and begin working on it (only the mitosis vs. meiosis side)

Genetic Variability Depending on how the chromosomes line up at the equator during Metaphase I, four gametes with four different combinations of chromosomes can result. (Independent Assortment) Genetic variation also is produced during: crossing over (during Prophase I) Fertilization (when gametes randomly combine)

Review Spermatogenesis and Oogenesis

Genetic Variability Animation http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#

Do Now: Label the phases of meiosis

Do Now – Period 3 How many autosomes? How many sex chromosomes? What is the sex of this patient? Monosomy, Trisomy? Is this individual normal?

Do Now Match the description to the phase of meiosis. A. Prophase I 1. Sister Chromatids are pulled apart. _____ A. Prophase I 2. Homologous chromosomes line up in the middle of the cell._____ B. Metaphase I 3. 2 daughter cells are formed ____ C. Telophase I 4. Nuclear membrane disappears__ D. Anaphase II 5. Nuclear membrane reforms around 4 cells ____ E. Anaphase I 6. Homologous chromosomes are pulled apart ____ F. Telophase II