gametogenesis

GAMETOGÉNESIS
ABSTRACT
Gametogenesis is the production of haploid sex cells (in humans, ovum and
spermatozoa) that each carry one-half the genetic compliment of the parents from the
germ cell line of each parent.
The production of ovum is termed oogenesis and the production of spermatozoa is
called spermatogenesis. Both oogenesis and spermatogenesis provide a mechanism
through whichgenetic information may be passed to offspring. The fusion of
spermatozoa and ova during fertilization results in a zygote with a fully restored diploid
genome.
The production of male and female gametes a highly complex and coordinated sequence
of a mitotic division, two meiotic divisions, cytoplasmic apportionment (divisions) and
cellular differentiation.
In eukaryotic organisms the gametes arederived from primordial germ cells, which
enter the gonads during early development. During embryogenesis, the primordial germ
cells are determined early in development by the presence of a cytoplasmic component
termed germ plasm. Once germ cells are determined they follow a different maturation
and, of course, genetic function, than do the remaining somatic cells of the body.
Primordial germcells are the stem cells that, via mitosis, supply both spermatogonia
and oogonia.
In humans, spermatogenesis starts with a diploid (2N) spermatogonium that carries the
full genetic compliment of 46 chromosomes (22 autosomal pairs, one X and one Y sex
chromosomes). The spermatogonium represents the germ cell line from which all sperm
cells are derived. Sequentially, the process ofspermatogenesis via mitosis produces a
primary spermatocyte that is also diploid (2N) and then via meiosis, two secondary
spermatocytes that are haploid (N). The haploid secondary spermatocytes carry 22
autosomes and either an X or a Y sex chromosome. The secondary spermatocytes each
undergo a second meiotic division to form a total of four haploid spermatids.
Subsequently, nurtured by surroundingsomatic cells, through the process of cellular
differentiation the four spermatids produce 4 sperm cells capable of motility and
fertilization

In human females the germ cell line is represented by the diploid (2N) oogonium that
carries the full female genetic compliment of 22 autosomal pairs and two X
chromosomes. Mitotic division yields a diploid primary oocyte. Meiotic divisions then
produceone female gamete--the ovum. In humans, the first meiotic division is
suspended in the diplonema stage during embryonic development. Meiosis resumes, one
ovum at a time following puberty and during the ovulatory period of the menstrual
cycle. Maturation proceeds with the production of haploid (N) secondary oocytes with
22 autosomal chromosomes and an X sex chromosome (the sex chromosome mustbe an
X chromosome because normal human females carry two X chromosomes and no Y
chromosomes). Also formed is a haploid polar body that is nearly devoid of cytoplasmic
contents. This is a fundamental difference between male and female Gametogenesis. In
males, there is a nearly equal divison of cytoplasm to the gametes, in females the
cytoplasmic contents are preserved for the eventual "egg"or ovum. Extraneous genetic
material is removed via polar bodies. Another meiotic division results in the production
of an ootid and yet another polar body (the eventual number of polar vies associated
with an ovum may equal as many as three if the first sloughed off polar body undergoes
a subsequent division. Cellular differentiation of the ootid yields an ovum ready for
fertilization. Inmany cases, however, the last maturational processes are accelerated
because in human females, meiosis II is usually completed after fertilization.

1.

INTRODUCCION

La reproducción es la capacidad que los seres vivos tienen para perpetuarse y dar lugar
a otros individuos semejantes a ellos y constituye una función básica de todo
organismo.

Los detalles del proceso reproductivo varían...