11-4 meiosis 9-3 meiosis - western coventry schoolfaculty.coventryschools.net/stetsonpeter/microsoft...

11-4 Meiosis9-3 Meiosis

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Copyright Pearson Prentice Hall

11-4 Meiosis

Each organism must inherit a single copy of every

gene from each of its “parents.”

Gametes are formed by a process that separates the

two sets of genes so that each gamete ends up with

just one set.

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just one set.

11-4 Meiosis Chromosome Number

Chromosome Number

All organisms have different numbers of chromosomes.

A body cell in an adult fruit

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A body cell in an adult fruit fly has 8 chromosomes: 4 from the fruit fly's male parent, and 4 from its female parent.


These two sets of chromosomes are homologous.

Each of the 4 chromosomes that came from the male

parent has a corresponding chromosome from the

female parent.

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A cell that contains both sets of homologous

chromosomes is said to be diploid.

The number of chromosomes in a diploid cell is

sometimes represented by the symbol 2N.

For Drosophila, the diploid number is 8, which can be

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For Drosophila, the diploid number is 8, which can be

written as 2N=8.


The gametes of sexually reproducing organisms

contain only a single set of chromosomes, and

therefore only a single set of genes.

These cells are haploid. Haploid cells are

represented by the symbol N.

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represented by the symbol N.

For Drosophila, the haploid number is 4, which can

be written as N=4.

11-4 Meiosis Phases of Meiosis

What happens during the process of meiosis?

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Phases of Meiosis

Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half

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chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

11-4 Meiosis

Meiosis involves two divisions, meiosis I and

meiosis II.

By the end of meiosis II, the diploid cell that

entered meiosis has become 4 haploid cells.

Phases of Meiosis

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Meiosis I

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Prophase I Metaphase I Anaphase I Telophase Iand

Cytokinesis

Interphase I

Meiosis I


Cells undergo a round of

DNA replication, forming

duplicate chromosomes.

Interphase I

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Each chromosome pairs

with its corresponding

homologous

chromosome to form a

tetrad.

MEIOSIS I Prophase II

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There are 4 chromatids in

a tetrad.


When 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.

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alleles.


Spindle fibers attach to

the chromosomes.

MEIOSIS I Metaphase I

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MEIOSIS I Anaphase I

The fibers pull the

homologous

chromosomes toward

opposite ends of the

cell.

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MEIOSIS I Telophase I and Cytokinesis

Nuclear membranes form.

The cell separates into two

cells.

The two cells produced by

meiosis I have

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meiosis I have

chromosomes and alleles

that are different from each

other and from the diploid

cell that entered meiosis I.


Meiosis II

The two cells produced by meiosis I now enter a

second meiotic division.

Unlike meiosis I, neither cell goes through

chromosome replication.

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Each of the cell’s chromosomes has 2 chromatids.


Meiosis II

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Telophase II

and Cytokinesis

Prophase II

Metaphase II Anaphase IITelophase I and Cytokinesis I

Meiosis II


Meiosis I results in two

haploid (N) daughter

cells, each with half the

number of chromosomes

as the original cell.

MEIOSIS IIProphase II

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The chromosomes line

up in the center of cell.

MEIOSIS II Metaphase II

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The sister chromatids

separate and move

toward opposite ends of

the cell.

MEIOSIS II Anaphase II

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Meiosis II results in four

haploid (N) daughter cells.

MEIOSIS II Telophase II and Cytokinesis

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11-4 Meiosis Gamete Formation

Gamete Formation

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

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11-4 Meiosis Gamete Formation

In many female animals, only one egg results from

meiosis. The other three cells, called polar bodies,

are usually not involved in reproduction.

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11-4 Meiosis Comparing Mitosis and Meiosis

How is meiosis different from mitosis?

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Comparing Mitosis and Meiosis

Mitosis results in the production of two genetically identical diploid cells. Meiosis produces four genetically different

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produces four genetically different haploid cells.


Mitosis

• Cells produced by mitosis have the same number

of chromosomes and alleles as the original cell.

• Mitosis allows an organism to grow and replace

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cells.

• Some organisms reproduce asexually by mitosis.


Meiosis

• Cells produced by meiosis have half the number

of chromosomes as the parent cell.

• These cells are genetically different from the

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diploid cell and from each other.

• Meiosis is how sexually reproducing organisms

produce gametes.

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11-4

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11-4

If the body cells of humans contain 46

chromosomes, a single sperm cell should have

a. 46 chromosomes.

b. 23 chromosomes.

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c. 92 chromosomes.

d. between 23 and 46 chromosomes.

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During meiosis, the number of chromosomes

per cell is cut in half through the separation of

a. daughter cells.

b. homologous chromosomes.

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c. gametes.

d. chromatids.

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The formation of a tetrad occurs during

a. anaphase I.

b. metaphase II.

c. prophase I.

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c. prophase I.

d. prophase II.

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In many female animals, meiosis results in the

production of

a. only 1 egg.

b. 1 egg and 3 polar bodies.

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c. 4 eggs.

d. 1 egg and 2 polar bodies.

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Compared to egg cells formed during meiosis,

daughter cells formed during mitosis are

a. genetically different, while eggs are

genetically identical.

b. genetically different, just as egg cells are.

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b. genetically different, just as egg cells are.

c. genetically identical, just as egg cells are.

d. genetically identical, while egg cells are

genetically different.

END OF SECTIONEND OF SECTION

11-4 meiosis 9-3 meiosis - western coventry schoolfaculty.coventryschools.net/stetsonpeter/microsoft...

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