Introduction to Gametogenesis
From MyMCAT
Introduction
Development begins at fertilization and is primarily determined by the genetic code of the fertilized zygote. Gametogenesis is the formation of the gametes which are used in sexual reproduction to produce zygotes. In the male testis, the process is known as spermatogenesis, while in the female ovaries, it is known as oogenesis.
Meiosis
Any cell in our body is normally diploid, containing 2n chromosomes (pairs of n chromosomes). Mitosis simply doubles this number and then splits it between two offspring cells, thus returning the number to 2n. Meiosis on the other hand, which only occurs in primordial germ-line cells, ie the gonads, produces gamete cells with a reduced amount of DNA, 23 chromosomes (1n, not paired) and when combined with a gamete from an individual of the opposite sex, returns the number to 2n (46 chromosomes, or 23 pairs).
Spermatogenesis
Spermatozoa (male gametes) are formed in the testis through meiosis known as spermatogenesis. At puberty, spermatogenesis gives rise to sperm through a series of events. After the initial DNA synthesis and crossing over, the first round of meiosis forms two primary spermatocytes (now each with 46 chromosomes). A second round of meiosis then reduces each of these primary spermatocytes into two secondary spermatocytes (4 in total) which now contain 23 chromosomes. Once
