Meiosis James GalaNTe, Chris Carillo, Collin cheUng, Riley Cohen

A Quick Overview of Meiosis

Meiosis is a type of cell reproduction that starts with a diploid germ cell and ends with 4 haploid gametes (sperm/egg cells).

Meiosis starts with one diploid cell and ends with four haploid cells.

Some things that should be understood before we go on

A Chromosome does not have to consist of two chromatids. A chromosome can have one chromatid and still be considered a chromosome.

Meiosis has two parts, Meiosis I and Meiosis II.

Gametes can not go through meiosis again, so they are stored in the gonads, which are the ovaries or testes.

Meiosis I is preceded by interphase in which the DNA is replicated, but Meiosis II is not preceded by a period of interphase, so the DNA is not replicated.

Tetrads are a pair of homologous chromosomes

Homologous means the same

Meiosis I

Prophase I

In Prophase I, each chromosome condenses and matches up with its homologous pair, which create tetrads, and crossing-over occurs. Crossing over is the exchanging of segments of two chromosomes, which makes each sex cell different from each other. The nuclear envelope starts to dissolve during this stage and spindle fibers attach to the chromosomes.

Metaphase I

The tetrads (homologous pairs) are aligned between the two spindle poles. This is preparing for the separation of the pairs.

Anaphase I

In this phase, the tetrads are separated and the chromosomes are pulled to opposite ends of the cell via spindles.

Telophase I

This is the phase where two haploid cells are formed. The separated chromosomes from Aanaphase I are pulled into groups and a nuclear envelope forms around them.

Meiosis II

Prophase II

In both haploid cells, the chromosomes condense, the nuclear envelope dissolves, and the spindle fibers attach to the chromatids.

Metaphase II

The chromosomes are aligned in the middle of the cell via spindle fibers in each cell.

Aanaphase II

The chromatids are pulled apart in both haploid cells by the spindle fibers and are pulled towards opposite poles.

Telophase II

Four nuclear envelopes form around 4 sets of 23 chromosomes. This is the last stage of Meiosis, and it is at this point when the four haploid cells are formed.

Meiosis Explained With Numbers

In this section I will explain how chromosomes and chromatids are affected during Meiosis.

Meiosis I

Starts with - 46 Chromosomes; 92 Chromatids

Prophase I

46 Chromosomes; 92 Chromatids; 23 Tetrads (1 tetrad = 2 chromosomes and 4 chromatids)

Metaphase I

46 Chromosomes; 92 Chromatids; 23 Tetrads

Anaphase I

Tetrads split; 2 sets of - 23 Chromosomes; 46 Chromatids; 0 Tetrads

Telophase I

2 sets of - 23 Chromosomes; 46 Chromatids

Meiosis II

2 sets of - 23 Chromosomes; 46 Chromatids

Prophase II

2 sets of - 23 Chromosomes; 46 Chromatids

Metaphase II

2 sets of - 23 Chromosomes; 46 Chromatids

Anaphase II

4 sets of - 23 Chromosomes; 23 Chromatids

Telophase II

4 sets of - 23 Chromosomes; 23 Chromatids

Created By
James Galante
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