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Okay, I was learning about mitosis and meiosis in school and had a question. I know in Mitosis you first start off with a Diploid (2N) cell and then end up with two daughter cells that are also Diploid. However, in Meiosis, I know you end up with four Haploid Cells (N), but what exactly do you start off with? Is it like a single egg makes four more eggs or something? Or does it start off with a Diploid Cell and then end up with the Haploids? If so, what exactly is the starting cell called?

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up vote 5 down vote accepted

Meiosis starts with a diploid cell and produces four haploid cells. In animals, the starting diploid cell is usually called a germ cell and the surviving haploid cells become gametes (sperm and ova). (In animals, the female mitotic sequence produces only one ovum; the other three haploid cells become "polar bodies".)

In other organisms such as plants, the starting diploid cell is typically not called a "germ cell" as it is not distinguished early in the organism's life. Instead the starting cell can be any undifferentiated diploid cell that finds itself in the appropriate location (e.g. in a flower) at the appropriate time.

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Thanks This is what I was looking for. – Link Jan 13 '13 at 18:06

During mitosis a diploid cell (2n = two copies of each chromosome, one from each parent) replicates its DNA so that it now has four copies of each chromosome. Then it divides, each daughter cell receives two copies of each chromosome and is again 2n.

In meiosis a diploid cell (2n) replicates its DNA so that it now has four copies of each chromosome. Then it divides, each daughter cell receives two copies of each chromosome and is again 2n. Then each of these divides once more without replicating DNA so that there are now four cells each with one copy of each chromosome (1n).

You might be tempted to think of a diploid cell which has replicated its DNA as tetraploid, but this word is not normally used in this context, since this is a transient 4n state.

This is a very broad overview. Have a look at the Wikipedia entry for meiosis to get a more detailed view and extended terminology.

@mgkrebbs (in comments):

If we are considering the meiotic divisions that create gametes, then in spermatogenesis the cell which undergoes meiosis is a primary spermatocyte, and in oogenesis it is a primary oocyte. Primary spermatocytes and primary oocytes are both diploid cells which undergo DNA replication before entering meiosis I.

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Unfortunately, this answer does not answer the main question, stated in the title as "What type of cell do you start with in Meiosis?" and in the last sentence of the question body as "what exactly is the starting cell called?". – mgkrebbs Jan 12 '13 at 20:47

Meiosis starts with a somatic (diploid) cell. To make a long story very, very short, this one cell undergoes cytokinesis twice. You end up with four haploid cells, called gametes or sex cells.

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