MEIOSISQ2 WK3 D2

Meiosis

Meiosis is the type of cell division by which germ cells (eggs and sperm) are

produced.

One parent cell produces four daughter cells.

Daughter cells have half the number of chromosomes found in the parent cell

MeiosisDuring meiosis, DNA replicates

once, but the nucleus divides twice.

There are 2 parts to Meiosis:

1. Meiosis 1

2. Meiosis 2

The 4 new daughter cells have variation of the parent DNA; this is genetic variation

Meiosis Terminology• Karyotype: Arranging of chromosomes from

largest to smallest; pairing up the homologous chromosomes

• Autosomes: All non-sex chromosomes; (#1-22 for humans)

• Sex Chromosomes: Chromosomes that determine the sex of an organism (#23 for humans)

• Set (n): # of different chromosomes. REMEMBER: Haploid = 1set, Diploid= 2 sets

Amniocentesis

Karyotype of a human• Is this person male or

female?

• How many sex chromosomes are present?

• How many autosome chromosomes are present?

• How many homologous pairs of chromosomes are present?

Background on Meiosis

• Meiosis involves 2 divisions of the nucleus– Meiosis 1 & Meiosis 2

Meiosis STARTS with HOMOLOGOUS CHROMOSOMES

Homologous Chromosomes: They are similar in shape, size & genetic content

Meiosis 1: 1st Division of Meiosis• Prophase I: Chromosomes

condense, nuclear envelope breaks, homologous chromosomes pair at ends.

• ***Cross-Over: Part of chromatid on 1 homologous chromosome exchanges with the other chromosome***

DRAW ME

THIS ISGENETIC

VARIATION

Meiosis 1: 1st Division of Meiosis• Metaphase I: Homologous chromosomes

move to center of the cell by the spindle fibers.

• Anaphase I: Homologous chromosomes separate and move to opposite poles, BUT sister chromatids stay together. A set of chromosomes moves to each pole

• Telophase I: The spindle fibers disappear, cells begin to cleave; still, two sets of chromosomes are at opposite poles

Meiosis 1

End of Meiosis I

• Once Meiosis I is complete, cytokinesis occurs and the cell splits into 2 haploid cells. These 2 cells enter Meiosis II

Meiosis I: STOP & THINK1. What is the purpose of Meiosis?

2. Describe genetic variation

3. Explain purpose of karyotyping

4. Explain cross-over

5. What major event occurs in Anaphase I ?

6. Are the daughter cells haploid or diploid? Explain

Any questionson Meiosis I

?????

Meiosis I: Video

• http://www.youtube.com/watch?v=D1_-mQS_FZ0

Meiosis II• Prophase II: A new spindle forms around the

chromosomes (no longer HOMOLOGOUS CHROMOSOMES)

• Metaphase II: Chromosomes line up at center & spindle fibers attach to centromere

• Anaphase II: Centromeres split, chromatids move to opposite poles of cell

• Telophase II: Nuclear envelope forms around each set of chromosomes & spindles retracts, cell begins cytokinesis

Result of Meiosis II• 4 HAPLOID cells form as a result of Meiosis II

• Haploid = cell containing 1 set of chromosomes

Meiosis II: 2nd division of Meiosis

Prophase II

http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html

Metaphase II

http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html

Telophase II

http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html

Meiosis I & II Venn Diagram

Meiosis I Meiosis II

Meiosis Booklet 1. Everyone needs 3 sheets of blank paper

2. Fold each one hotdog style3. Cut straight up the fold

(You should have 6 long sheets, only use 5)

4. Label each square with the phases of meiosis the same as the mitosis booklet

Meiosis Review Questions 1. What type of cells are

used in Meiosis? Give examples of these cells.

2. Meiosis is used in sexual reproduction. Explain the process of “cross-over”

3. Draw homologous chromosomes going through cross-over.

4.Meiosis is divided into two parts, why?

5. Define “Haploid”

6. Compare and Contrast Meiosis to Mitosis.

In your notebook!

Mitosis & MeiosisComparison Worksheet

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

http://www.usoe.k12.ut.us/curr/science/sciber00/7th/genetics/sciber/animatin.htm

Meiosis & Genetic Variation

Q2 WK4 D2Nov. 5th, 2013