PSL201Y1 Lecture Notes - Seminiferous Tubule, Sex Steroid, Spermatozoon

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Published on 29 Nov 2011
School
UTSG
Department
Physiology
Course
PSL201Y1
The hormonal regulation of reproduction
Gametes
Sexual reproduction occurs by the fusion of gametes which in
males are the spermatozoa and ova in females. Each gamete contains
half of the usual number of chromosomes so are haploid, they contain
23 sets of chromosomes. This is referred to as n chromosomes. All
other cells of the body are said to be diploid because they contain 46
sets of chromosomes and are referred to as 2n chromosomes.
During reproduction, gametes from each parent fuse together to
produce a new cell. This new cell, a zygote, is diploid because it has
received one set of chromosomes from each parent.
Chromosomes
Spermatozoa and Ova contain 23 chromosomes. 22 of these
chromosomes are called autosomes. Autosomes are the chromosomes
that determine everything except an individual’s sex. Sematic cells, all
cells of the body except gametes contain two sets of 22 autosomes.
Each autosome in a pair carries the same complement of genes and is
so said to be homologous. The remaining one chromosome of the two
sets of 23 chromosomes and diploid cells is the sex chromosome that
determines an individual’s sex. There are two types of sex
chromosomes: X and Y. The female set of chromosomes is XX and
males are XY. Unlike autosomes, the X and Y chromosomes are
distinguishable from each other on the basis of their shape. Because
the sex chromosomes differ, they are said to be non homologous. The
X and Y chromosomes share very few genes. For example the sex
determining gene is only present on the Y chromosome. This gene has
the responsibility of determining that the individual becomes male.
Lack of this gene will mean that the determining organism will become
female.
Gametogenesis
The process in which gametes are produced is called
gametogenesis. This process differs in many ways from the process in
which somatic cells are derived.
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Cells in the body are derived through a process called mitosis
which is normal cell division. In a cell undergoing mitosis, the DNA is
replicated so for a short time, the cell contains 4 copies. After it
divides, it only contains 2 copies of the chromosomes, the parent cell
and the new cell each with 2 pairs of chromosomes.
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The production of gametes occurs by a different, more complex
process called meiosis. Meiosis differs in two fundamental ways from
mitosis. In meiosis, DNA undergoes replication only once and cells
undergo division twice. This reduces the number of chromosomes in
each cell by half from 2n to n, from diploid to haploid. Eventually, the
cells finishing this process become mature ova and spermatozoa.
There is reassortment of genes and the production of unique cells with
a unique combination of both parent’s genes. This occurs in a process
called non homologous recombination or “crossing over”. Genetic
reassortment is the basic for variation in DNA between individuals of
the species.
Hormonal control of reproduction
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Document Summary

Sexual reproduction occurs by the fusion of gametes which in. During reproduction, gametes from each parent fuse together to males are the spermatozoa and ova in females. Each gamete contains half of the usual number of chromosomes so are haploid, they contain. All other cells of the body are said to be diploid because they contain 46 sets of chromosomes and are referred to as 2n chromosomes. produce a new cell. This new cell, a zygote, is diploid because it has received one set of chromosomes from each parent. chromosomes are called autosomes. Autosomes are the chromosomes that determine everything except an individual"s sex. Sematic cells, all cells of the body except gametes contain two sets of 22 autosomes. Each autosome in a pair carries the same complement of genes and is so said to be homologous. The remaining one chromosome of the two sets of 23 chromosomes and diploid cells is the sex chromosome that determines an individual"s sex.

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