aim: what events take place at each phase of meiosis? do now: what is the difference between gametes...

AIM: What events take place at each phase of meiosis?

• DO NOW: What is the difference between gametes and body (somatic) cells? Define Homologous Chromosomes

• VOCABULARY: meiosis, diploid, haploid, gamete, tetrad, homologous chromosomes, crossing over

• New updated syllabus!

• Hand in New York Times Article Summary

• HW due next Tuesday read chapter 11-4. Answer questions pg 278 #1-5

• Quiz on Meiosis Wednesday 2/24

• HAVE A GREAT VACATION!

Review of Do Now

• What is the difference between gametes and body (somatic) cells?

• Define Homologous Chromosomes

Overview of Meiosis

• Diploid Vs. Haploid• 2 cell divisions

– 4 haploid daughter cells

• Reduction of chromosome number 2nn• Homologous chromosomes• Contributes to genetic diversity

– New combinations of chromosomes– Crossing over during prophase I


• Do Now: What are homologous chromosomes? What is the goal of meiosis? What is crossing over?


• HW due tomorrow Read Chapter 11-4. Answer questions pg 278 1-5

• Wednesday Quiz on Meiosis (Chapter 11-4)

• HW due Friday Pg 1025, ques 1-19 and 22

The Phases of Meiosis Meiosis I• Prophase I*• Metaphase I*• Anaphase I*• Telophase I• * indicates significant

differences from mitosis

Meiosis II• Prophase II• Metaphase II• Anaphase II• Telophase II• Events in all phases

of meiosis II are very similar to mitosis.

IN YOUR NOTEBOOKS: Outline events and sketch cells in each phase of meiosis I and II. Chart Three columns—Name of phase, events, sketch.

Crossing Over

Meiosis I

Interphase I

Cells undergo a round of DNA replication, forming duplicate Chromosomes.

Prophase I

Each chromosome pairs with its corresponding

homologous chromosome to form a tetrad.

Metaphase I

Spindle fibers attach to the chromosomes.

Anaphase I

The fibers pull the homologous chromosomes toward the opposite ends of

the cell.

Meiosis II

Prophase IIMeiosis I results in two

haploid (N) daughter cells, each with half the number of chromosomes as the original.

Metaphase II

The chromosomes line up in a similar way to the metaphase

stage of mitosis.

Anaphase II

The sister chromatids separate and move toward opposite ends of the cell.

Telophase IIMeiosis II results in four

haploid (N) daughter cells.

Questions

• How could the final products of meiosis be different than the ones shown in the diagram?

• Are these the only possible products of meiosis for the cell in the diagram? Explain.

• In your groups:

Where does this different arrangement originate (which phase of meiosis)?


• Do Now: How could a cell have 46 chromosomes and be haploid?


• Have out HW

• Quiz tomorrow on Meiosis (Chapter 11-4)

• HW due Friday Pg 1025, ques 1-19 and 22

Review of HW• Describe the main result of meiosis

– Four haploid cells genetically different from each other and from the original cell

• What do the terms diploid and haploid mean?– Diploid: two sets of chromosomes; haploid is one set of

chromosomes• What is crossing over?

– Homologous chromosomes pair up and form tetrads, which may exchange portions of their chromatids, resulting in the exchange of alleles between the homologous chromosomes

• In human cells 2N=46. How many chromosomes would you expect to find in a sperm cell? In an egg cell? In a white blood cell? Explain.– Both sperm and egg cells have 23 chromosomes because they

are gametes, which are haploid cells. A white blood cell has 46 chromosomes because it is a diploid body cell.

Compare and Contrast Mitosis vs. Meiosis

• Function

• Location in Body

• Number of Daughter Cells

• Change in Chromosome Number

• Number of Phases

• Number of Cell Divisons

• Difference in DNA between parent cell and daughter cells

Review of Meiosis• How many phases are there?

• What is a tetrad and when does it form?

• When does crossing over take place?

• What happens in metaphase I, anaphase I and telophase I?

• What happens in metaphase II, anaphase II and telophase II?

• Which stage of meiosis is most like mitosis?

• What do you think would happen if the homologous pairs didn’t fully separate during anaphase I?

Movie Continued

aim: what events take place at each phase of meiosis? do now: what is the difference between gametes...

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