Cell Cycle, Mitosis, and Meiosis (page 275) - WAHS

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Unit 7: Cell Growth and Division

Section 4: Meiosis

Chromosome Number

All organisms have different numbers of chromosomes. A body cell in an adult fruit fly has 8 chromosomes:

4

from the male parent and

4

from its female parent. Homologous

- each chromosome that came from the male parent has a corresponding chromosome from the female parent.

Haploid and Diploid Cells

A cell that contains both sets of homologous chromosomes is said to be

diploid

This is sometimes represented by the symbol

2N

. For the fruit fly, it would be written like this:

2N = 8.

When a cell only has a single set of chromosomes, the cell is considered

haploid

This is sometimes represented by the symbol

N.

Gametes-

specialized cell involved in sexual reproduction. Only contains half the necessary genetic material. (Sex cells such as sperm and eggs.)

Humans have

46

chromosomes in a diploid cell.

23

in a haploid cell.

The Process of Meiosis

Meiosis is a process of

reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

Meiosis is divided into two parts

Meiosis I

and

Meiosis II.

Label each part of Meiosis I

Interphase I Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis

Label each part of Meiosis II

Interphase II Prophase II Metaphase II Anaphase II Telophase II & Cytokinesis

Prophase I

: Each chromosome pairs with its corresponding homologous chromosome to form a

tetrad.

There are

4

chromatids in a tetrad. Homologous chromosomes can exchange portions of their chromatids in a process called

crossing over

. This allows for different combinations of genes.

Comparing Mitosis and Meiosis

Metaphase I, Anaphase I, and Telophase I are all the same as in

mitosis.

The goal of mitosis is to create two

identical

daughter cells. Meiosis results in four

haploid

(N) genetically

different

daughter cells.

Differences in Meiosis

The female sex cell is called

egg

and the process is called

oogenesis.

The male sex cell is called

sperm

and the process is called

spermatogenesis.

In both cases, meiosis begins with

one

cell that divides. In oogenesis, only

1

viable (living) egg is produced and the remaining 3 are called

polar bodies

. In spermatogenesis,

4

viable sperm are produced.

Draw the flow chart for Oogenesis. Draw the flow chart for Spermatogenesis.

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