Gametogenesis is the formation and production of specialised cells called Gametes, also known as sex cells or germ cells. In females the gametes are oocytes and in males they are spermatocytes.
Etymology of Gametes: Originally from Greek, with Gamos meaning marriage. Later on the word split into Gametes and Gamete meaning husband and wife respectively. The word was adapted in Modern Latin, Gameta and eventually ended up as Gametes as its known today!
Meiosis Breakdown
Meiosis 1
The figure above shows a simplified version of chromosomes within a cell. There are 23 pairs of chromosomes in a Diploid cell (2n), however it would be too difficult to demonstrate all 23 pairs so we are only showing two in this scenario. During meiosis 1, the original cell (the primitive germ cell) undergoes S phase Interphase: where the DNA is replicated and is now paired which is demonstrated in the first 2 cells (left to right). After Interphase the cell undergoes Prophase 1 in which the chromosomes undergo Synapsis, the means that the pairs of chromosomes come together and wrap around each other and under go Cross-over (this is important to allow for variation to occur!) this is seen in the 3 and 4th cell (from the left). In the 5th cell we can see the chromosomes lining up in the centre of the cell this occurs during Metaphase 1: Independent Orientation. The remaining three cells we can see yellow Spindles being produced from the centrosomes and attaching to the black centre of the chromosome called a centromere, these spindles pull the chromosomes either side. During Telophase 1 and cytokinesis the last cell is divided into two cells (resulting in the first of two divisions occurring during Meiosis).
Meiosis 2
Following in from Telophase 1 and cytokinesis which occur in Meiosis 1 the cell has now divided completely into two separate cells. In Meiosis 2, prophase, metaphase, anaphase and telophase occur in the same way, diving the chromosome number in half again, however it has to be noted that there is no DNA replication occurring in Meiosis 2! The last division of Telophase 2 and cytokinesis as seen in the last group of cells results in 4 separate cells. These cells are known as Haploid Daughter Cells this is because they contain half the genetic information/chromosome number than the original primitive germ cell. It should be noted that gametogenesis in both males and females (sex that was assigned at birth) produce 4 Haploid Daughter Cells through meiosis but this process occur at different times. Males (assigned at birth) commence Gametogenesis at puberty and continues until death, however for Females (assigned sex at birth) commence gametogenesis around the 5th month of foetal development but during Prophase 1 the gamates go into a state of dormancy any remain in meiotic arrest in the ovaries until puberty, this arrest during the first meiotic division may last up to 40 years in females. Also in females not all four Daughter Cells result in gametes, only 1 will mature into an oocyte, the remaining three usually dont receive any cytoplasm and degenerate through further development.
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