Gametes are cells produced for sexual reproduction, with humans having two types: eggs and sperm. They each have 23 chromosomes and are formed through meiosis. The 23rd chromosome pair determines biological sex. Meiosis allows for genetic diversity in gametes. Sperm are small and motile, while eggs are large and provide nourishment for embryos. Spermatogenesis occurs in the testicles, while oogenesis occurs in the ovaries. Fertilization unites the gametes into a zygote with 46 chromosomes.
A gamete is a cell produced by an organism for the purpose of sexual reproduction. In man, egg and sperm are the two sex cells, which differ in their size and other qualities such as the quantity of each that the body produces. Each of these cells has 23 chromosomes, exactly half the number found in other cells in the body. They are formed by a special cell division called meiosis, which occurs only in the primary sexual organs – the testicles and ovaries. Fertilization unites the gametes of both parents into one zygote.
Sexual organisms create a special type of cell, the gamete, which combines with another cell for reproduction. In humans, each of these cells contains one pair of 23 chromosomes, and therefore is haploid, while the other cells are diploid, with two pairs of chromosomes. The 23rd pair differs in males and females, and is what biologically distinguishes the two sexes, with males having the XY pair and females having the XX pair. Chromosomes are made up of long strings of genes strung together in a sequence. Since the egg or ovum, the female cell, can only carry X chromosomes, sex is determined by the male gamete.
The normal division of cells to produce a new copy of the original occurs through a process called mitosis. A slightly different division, meiosis, generates a new gamete. Both processes involve copying DNA from the parent cell’s nucleus and transferring it to the new one, but meiosis involves a special combination of DNA from both of the parent’s original gametes. This recombination of hereditary information allows for diversity of hereditary traits in the newly produced gamete; it is why children have a blend of genes from both parents.
Size and relative quantity distinguish the male from the female gamete. Male gametes, sperm, are motile, small, and produced in large numbers, few of which reach fertilization. Eggs, the female cell, are large, with cytoplasm that will nourish an embryo if fertilization occurs. Some species of algae and plants do not have separate male and female gametes, but reproduce by combining genetically identical cells. In asexual species, no gametes are produced and cells divide only by mitosis.
The male gamete, the sperm, is produced in the testicle, in a process called spermatogenesis. Each testicular cell that undergoes meiosis produces four new gametes. In the female ovary, ovarian follicles generate oocytes during a process called oogenesis that occurs largely at birth but is completed after puberty during the monthly ovarian cycles, when the eggs mature and become ready to be fertilized. Upon fertilization, the gametes unite and a zygote is formed. This cell has 46 chromosomes, with an equal number provided by each parent.
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