Chapter 9, Part II - Meiosis
Developed by Nancy Manikas (6-29-97)

Why wouldn't regular cell division, mitosis, work to make gametes?

A. Chromosome Number

Each organism has a set number of chromosomes. For example, a human has ______ chromosomes. (karyotype)

A fruit fly (Drosophila) has ________ chromosomes.

- gets ______ from the male (father) and _______ from the female (mother).

- the fly received one chromosome #1 from its mother, and one chromosome #2 from its father. These corresponding chromosomes are called _______________. A cell with a full set of matching chromosomes (homologs) is called a ___________ cell (symbolized as 2N). It has two complete sets of chromosomes (one from mom and one from dad) and two complete sets of genes.

- gametes of organisms that reproduce sexually contain only a __________ set of genes (one set of chromosomes). These cells are called ___________ (represented as N).

For humans, N = _________

For Drosophila, N = _________

B. The Phases of Meiosis

Meiosis I:

DNA has already been _______________ before meiosis begins.

Prophase I looks like the prophase of mitosis.

Metaphase I: chromosomes seek out their matching pairs (homologous chromosomes) and line up in ________. At this point, chromosomes may exchange parts, called crossing-over. If this happens:

 

 

Anaphase I: the _______________ chromosomes are separated; ______________ do not split. Therefore, both sister chromatids go to the same cell. Resulting cells are not identical copies of the original cell like in mitosis.

Meiosis II:

No DNA ________________ first.

Chromosomes line up on the equator, split during anaphase II, so now each ____________ cell has the _____________ number of chromosomes (half the number the original parent cell had).

C. Gamete Formation

Males - haploid cells formed are called _______

- in plants, ________ contains the haploid cells.

Females -usually only one of the four haploid cells formed by meiosis is used for

______________. This one is called the __________ cell in an animal and the ___________ in a plant.

- in mitosis, the cell divisions are ____________.

- the egg receives most of the _______________.

- the other three cells formed are called _________ __________.