Starting with the Basics
by C. Williams

Genetic material, otherwise known as DNA (DeoxyriboNucleic Acid) is composed of millions of genetic instruction sets. Each "set" is actually a specific ordered sequence of only four different amino acids. (Adenine, Thymine, Guanine, and Cytosine). Each instruction set may be several hundred acid molecules long.

A "set" of instruction "code" (as it is sometimes referred to) is known as an Allele. Connect a large number of alleles together into a long "strand" and you have half of a Chromosome.

When you put two matching chromosome strands together, the "genetic code" or alleles match up on both sides, and together the two alleles are referred to as a Gene. In most body cells, chromosomes occur in pairs. This is what leads to the term "gene pair".

Each "gene", therefore, is actually comprised of a pair of alleles.

A particular area or location on a chromosome, is called a "locus" (plural = "loci"). The combination of both alleles at a specific locus determine a particular Trait or Characteristic of the animal. Hair color and eye color are examples of traits.

Most all of the cells in the body contain all of chromosomes. The chromosomes act as "instruction sets" which both tell the body how it will grow, develop and operate... the traits of the individual.

Each "color band" pair represents a Locus. The two alleles at each location, together represent a Gene When both alleles are the same, they are referred to as homozygous. When each allele within a pair is different, it is known as heterozygous.

Since the chromosomes occur in pairs... each "half" of the chromosome pair has the same order/arrangement of loci as the other. The exception to this, is the chromosome pair known as the Sex Chromosomes.

These chromosomes are often referred to as the X and Y chromosomes. The Y chromosome is shorter and contains less material than the X chromosome.

The specific combination of the sex chromosomes determine the gender or sex of the individual. Two X chromosomes (XX) will result in a female. The XY combination will result in a male.

Most of the cells in the body contain an entire set of genetic instructions or chromosome pairs. The primary exception to this, is in the specialized sex cells used for reproduction.

The reproductive cells, known as gametes, (which take the form of ova in females or spermatozoa in males) carry only half of the animal's genes. In all the higher species (such as mammals) the offspring will receive only one half of a gene pair from each parent.

In the process of cell division that creates these gametes, the existing chromosomes of the parent are allowed to "cross-over". That is, some of the alleles found on one side of the chromosome pair will randomly trade places with the alleles found on the other side. After this exchange, the cell divides, and each resulting gamete cell has only half of the genetic material of the parent.

As a result, each gamete contains a unique grouping of half of the genes of the parent animal. This special process of recombining the alleles to form gametes is known as Meiosis.

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Views expressed herein are those of the writers and compilers of the various information. Reference sources are cited where applicable. Copyrights are the property of the respective authors.