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An Introduction to Zoology:  Chapter 6
An Introduction to Zoology: Chapter 6
Published by The Lone Ranger
08-07-2008
Default Gametogenesis

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.

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  #1  
By monruw on 03-30-2011, 01:55 PM
Default Re: An Introduction to Zoology: Chapter 6

why it's called animal-vegetal axis? sound like kinda food, meat and vegetable or what else~ any story behind this?
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  #2  
By The Lone Ranger on 05-22-2011, 01:35 AM
Default Re: An Introduction to Zoology: Chapter 6

"Vegetal," is related to "vegetable." Many plants can reproduce asexually, whereas virtually all animals reproduce sexually.

Probably for this reason, "vegetal" came to refer to processes in living things that are "plant-like," especially processes that do not occur through sexual reproduction. More to the point, perhaps, plants generally grow much more slowly than do animals. So the "vegetal" pole of an egg gets its name for the fact that the cells in this region grow and divide much more slowly than do the cells in the "animal" pole.


Cheers,

Michael
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