Our body consists of microscopically small units called cells
that serve many different functions. The average human body
contains about 100 trillion cells, each of which can only be
made out if separated from the other cells visualized under a
specialized magnifying lens called a microscope. Cells come in a
variety of types; muscles for instance consists of cells that
can stretch and contract, whereas our brain and nerves have
cells that can transfer and store messages. There are many, but
a limited number, of different cells. Most cells consists of two
distinctive structures, the nucleus and the cytoplasm each of
which have even smaller features that have distinctly different
functions.
The cytoplasm is the machinery that drives the cell and operates
its features. The nucleus contains the genes that provide a
master plan that makes the cell operate in a certain way. Each
nucleus contains two complete sets of genetic information, with
the exception of the sperm and egg nucleus that contain only one
set. Our genes come in 23 separate pairs of packages called
chromosomes organized inside the cell’s nucleus. Together, the
packages contain the human genome often described in more
distinct units each with one or more functions, called genes.
Twenty-two of the chromosome pairs are ordered in size. The
number 1 chromosome is the largest and number 22 the shortest.
The 23rd pair consists of so-called sex
chromosomes, that come in two distinct varieties - two large
ones called X in women, and one X and a small Y in men. Y is the
smallest of all chromosomes and X is about as large as
chromosome 8. There is probably not much significance in the
fact that we have 23 chromosomes. Related species have either
more or less chromosomes. Likewise, genes that have a similar
function may be located on different chromosomes in different
species.
Modern genetics, the study of genes, is as laden with lingo and
jargon as any field of science. This is often intimidating for
the aspiring amateur geneticist or patient seeking advice in
understanding genetic disease or the use of genetic technology
such as detection of extra or missing chromosomes in cells taken
from embryos before transfer during assisted reproduction. It is
important to understand for instance that one set of the genes
in our cells comes from our mother and one set from our father.
This is true whether you are a woman or a man. Globally, each
set of parental genomes consists of about 19,000 genes, a number
that is not set in stone and actually goes up and down each day
depending on the information known to science. In all reality,
there are subtle but crucial differences between the parental
genomes. The reproductive cells or gametes can only pass on one
set of genes to the fertilized egg and embryo. In order to pass
on genes from both the parents of the person that is
reproducing, the genes are shuffled inside the unripe sperm and
egg cells, so that a single chromosome contains information from
both parents. This process is called recombination and is
essential for reproduction to occur normally. As a result the
embryo contains genes characteristic of all four grand-parents.
Recombination is typical for reproductive cells reducing their
two sets of genomes into one. It is a unique mechanism that is
only preserved for reproductive organs called ovaries and
testicles and it is only the reproductive cells in these organs
that undergo this special change.
The final product of the genome is the production of proteins,
specialized molecules that are the functional units performing
most of the processes in the cell. How does the gene produce the
protein it is uniquely created for? Well, in a way it doesn’t
produce proteins, but it provides a code of information with
which other molecules and sub-cellular structures called
ribosomes can manufacture the protein.
Genes consists of a specialized complex molecule called
DNA. DNA contains information organized in four different kinds
of so-called bases…more
to come.
