Gametogenesis:
Gametogenesis, of course, is the process by which the
gametes (sex cells) are formed. In most animals, normal body cells are
diploid, meaning that they have two sets of chromosomes – one set inherited from the mother and one set inherited from the father. These body cells reproduce through the process known as
mitosis, which produces cells that are diploid and genetically-identical to the original cell.
The gametes are produced in organs known as the
gonads. The male gonads are the
testes (
testicles) and they produce small, mobile gametes known as
spermatozoa. The female gonads are the
ovaries and they produce relatively large, non-mobile gametes known as
ova. Within the gonads, a different form of cellular division occurs, known as
meiosis. Meiosis results in cells that are
not genetically identical to the original cell, and that have only half the normal number of chromosomes. These cells are therefore referred to as
haploid, and they are the gametes.
After their production, the gametes are transported through tubes that make up the
reproductive tract and, ultimately, to the outside of the body. Of course, in those species with
internal fertilization, the female’s gametes are not expelled from the body, but are retained within the reproductive tract until after fertilization occurs.
The female’s ovum contains everything a cell needs in order to survive – except, of course, for half of its DNA. This is one reason why the ovum is typically far larger than is a spermatozoan; a spermatozoan is optimized for mobility and has lost absolutely everything that is not essential to the task of traveling to and fertilizing the ovum. To a first approximation, the father contributes only DNA to a zygote and the resulting embryo; everything else is contributed by the mother.
Reproductive anatomy of the human male: Spermatozoa are produced within the testes and
stored in the epididymis. During ejaculation, spermatozoa travel out of the scrotum through
the vas deferens and into the abdomen. The seminal vesicles, prostate gland and
bulbourethral (Cowper’s) glands secrete fluids that mix with the spermatozoa to
form semen. The semen continues out of the body through the urethra.
The reproductive tract of the human female: Ova are produced in the
ovaries. After ovulation (release of an ovum), the ovum is swept into a
Fallopian tube (oviduct
). If fertilization occurs, the zygote will implant
in the lining of the uterus. Otherwise, the ovum continues through the
uterus and out of the body through the vagina.
Gametogenesis
Linear Mode
