2. Meiosis and its Phases

Alternation of Generations

One member of every original pair of chromosomes end up in each resulting cell, which means each cell has one set of chromosomes. None of the daughter cells is identical to the parent cell. A cell with one set of chromosomes is called haploid and a cell with two sets is called diploid. In sum, a diploid cell undergoes meiosis and results in four haploid cells.

Sex cells, or gametes, of an organism, are haploid and when a zygote is formed, the zygote is diploid. This is always true, no matter how many chromosomes an organism might have. In many places, you will find it stated that an organism has n number of chromosomes. In this case, an organism will have 2n chromosomes in its diploid cells and 1n chromosomes in its haploid cells. Alternation of generations refers to a plant’s life cycle including sexual reproduction that is characterized by alternating between a diploid (2n) sporophyte phase and a haploid (1n) gametophyte phase.

Schematic diagram of the life cycle of plants. Note the alternation of sporophyte and gametophyte generations.

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