Meiosis

Chapter 10.1 and 11.3

Do Now

How is a baby made? On the cellular level, draw how a baby is

made. (NO PHALLIC SYMBOLS PLEASE!)

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?

Do Now

What is mitosis? What is meiosis? List 2 differences between the two?

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: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

Karyotype

Homologous Chromosomes

Same length Same centromere position Carry genes that control

the same inherited traits

Meiosis

The sexual life cycle in animals involves meiosis

Meiosis produces gametes.

When gametes combine in fertilization, the number of chromosomes is restored.

DNA Replication

PrepareGrowth

Division

Cell Cycle

Mitosis

Meiosis

2N

2N

N NNN

2N

Do Now

Label A, B, and C

(Hint same size, same shape…)

Meiosis

2 DivisionMeiosis 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

The spindles break down. Chromosomes uncoil and form two nuclei. The cell divides.

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.

Animation

http://www.cellsalive.com/meiosis.htm

Animations on Meiosis

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

Do Now: Label the phases of meiosis

Genetic Variability Depending on how the

chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result (independent assortment).

Genetic variation also is produced during crossing over

Random fertilization.

Genetic Variability Animation

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

Review Spermatogenesis and oogenesis

Think – Pair - Share Draw out the stages of meiosis using the

following cell. Make sure you draw the cell with crossing over of only one pair of homologous chromosomes! (use colored pencils)

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.

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

Review

How does meiosis promote genetic variability? List 3 reasons why.

THINK – PAIR - SHARE

If a hamster has 44 chromosomes in G1 phase of the cell cycle, then…How many chromatids are in G2 Phase?How many chromosomes are in the G2

Phase?How many chromosomes will be in each cell

after it has gone through mitosis?

Do Now

What two divisions do your cells undergo? What are the differences between the

two?