11-4 Meiosis Understand that homologous chromosomes separate randomly during meiosis to produce...

11-4 Meiosis

Understand that homologous chromosomes separate randomly during meiosis to produce haploid gametes.

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MT: Sexual Reproduction

11-4 Meiosis

CELL DIVISION:

MEIOSIS & SEXUAL

REPRODUCTION

Images: Peter, Lois & Stewie, The Family Guy From the Virtual Cell Biology Classroom on ScienceProfOnline.com

11-4 Meiosis

WHAT IS HAPPENING HERE?

11-4 Meiosis

FERTILIZATION

= when a male and female gamete join

11-4 Meiosis

CHROMOSOME # Most organisms are diploid and thus want an offspring

that is also diploid

So, each gamete has to be haploid so when they join they create a diploid organism

mitosis

meiosis

11-4 Meiosis

FIND CHROMOSOME #

DIPLOID #

Human 46 chromosomes Dog 78 chromosomes Carrot 18 chromosomes Goldfish 94 chromosomes Wheat 42 chromosomes Tobacco 48 chromosomes

HAPLOID #

Human __ chromosomes Dog __ chromosomes Carrot __ chromosomes Goldfish __ chromosomes Wheat __ chromosomes Tobacco __ chromosomes

11-4 Meiosis

haploid (n) + haploid (n) = diploid (2n)

Female gamete + male gamete = offspring somatic cell

½ + ½ = 1

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CHROMOSOME NUMBER

These two sets of chromosomes are homologous.

One chromosome from mom and one chromosome from dad.

11-4 Meiosis

HOMOLOGOUS CHROMOSOMES

• PairPair of chromosomes that contain the same alleles for a trait

• EX: chromosome with eye color allele from mom is homologous to chromosome with eye color allele from dad

Mom Mom (1,3)(1,3)

Dad Dad (2,4)(2,4)

11-4 Meiosis

WHICH PAIR UP TO MAKE HOMOLOGOUS CHROMOSOMES?

How many pairs of homologous chromosomes are shown?

How many chromosomes are shown?

Pink with pink; yellow with yellow; blue with blue

11-4 MeiosisWhat happens during the process of

meiosis?

making of non-identical making of non-identical haploid gameteshaploid gametes

11-4 Meiosis

PHASES OF MEIOSIS I

Meiosis I

Prophase I Metaphase I Anaphase I Telophase I and

Cytokinesis

Interphase I

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INTERPHASE 1

DNA copies itself

nucleusnucleus

centriolescentrioles

11-4 Meiosis

PROPHASE INuclear membrane disappears.

Homologous chromosomes pair up to form a tetrad.Tetrad = 4 sister chromatids

Crossing over occurs

11-4 Meiosis

CROSSING OVERWhen homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over.

Crossing-over produces new combinations of alleles.

Does crossing over always occur at the Does crossing over always occur at the same allele?same allele?

NO! It is NO! It is randomrandom

11-4 Meiosis

METAPHASE 1

Homologous chromosomes line up in middle of cellSpindle fibers attach to the chromosomes’ centromeres.

11-4 Meiosis

ANAPHASE 1

The fibers pull the homologous chromosomes toward opposite ends of the cell.

11-4 Meiosis

TELOPHASE 1

The cell separates into two cells

Nuclear membranes reappear

11-4 Meiosis

PHASES OF MEIOSIS II

Meiosis II

Telophase II and

Cytokinesis

Prophase II Metaphase II Anaphase IITelophase I and Cytokinesis I

11-4 Meiosis

Cells DO NOT need to grow or copy DNA since they are trying to get smaller

11-4 Meiosis

PROPHASE II

Nuclear membrane disappears.

11-4 Meiosis

METAPHASE II

Individual chromosomes line up in the middle of cell.

11-4 Meiosis

ANAPHASE II

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

11-4 Meiosis

TELOPHASE II

Meiosis II results in four non-identical haploid cells.

11-4 Meiosis

GAMETE FORMATIONIn male animals, meiosis results in four equal-sized gametes called sperm.

11-4 Meiosis

GAMETE FORMATIONIn many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction.

11-4 Meiosis

Image: Meiosis diagram, Marek KultysFrom the Virtual Cell Biology Classroom on ScienceProfOnline.com

View Meiosis Animation

11-4 Meiosis

Image: Mitosis diagram & Meiosis diagram, Marek Kultys From the Virtual Cell Biology Classroom on ScienceProfOnline.com

11-4 Meiosis

MITOSIS VS. MEIOSIS

Same genetic information in parent cell and daughter cell.

Give me another one just like the other one

Daughter cells different from parent cell and from each other.

Daughter cells have ½ the number of chromosomes as somatic cell.

Shuffling the genes(Mix it up!)

From the Virtual Cell Biology Classroom on ScienceProfOnline.com

11-4 Meiosis

WEBSITES TO CHECK OUT

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

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

3. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html

4. http://www.youtube.com/watch?v=uh7c8YbYGqo

11-4 Meiosis Understand that homologous chromosomes separate randomly during meiosis to produce...

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