A very short explanation would be a gene created by two very different genes.  We can in Canary terms see this as an out-cross, or as a result of type breeding two unrelated birds together.  Below is a far more technical explanation.

What does Heterozygous mean?

Heterozygous means an organism has two different alleles on its Homologous chromosomes.  In other words, the organism has more than one version of particular genes.

Give me an example:

Let's say we are looking at the gene that controls the Canaries height, and we will assume there are two versions of this gene, or two alleles: R = the tall allele, and r = the short allele.  A heterozygous Canary would have one of each on its Homologous Chromosomes, so the genotype would be Rr.

What are Homologous Chromosomes?

Homologous chromosomes are similar in shape and content and are separated during meiosis.  In a Canary that was produced during reproduction, each parent contributed a set of chromosomes grouped into homologous pairs.

Give me an example:

Every cell in your body has exactly 46 chromosomes.  Half were in an egg in your mother and the other half were carried to the egg by a sperm donated by your father.  Each of the 23 donated by one parent corresponds in shape and content to a chromosome in the set donated by the other parent.  These homologous chromosomes paired up to produce a unique you.

Pretend each of our parents gave you a set of encyclopedias, each with 23 volumes.  They both have similar information presented in a similar format, so the information in Vol. I from your Dad is similar to the information in Vol. I donated by your Mother.  Each may have a listing for "aardvark", but they may each say slightly different things about "aardvarks".  You have inherited two versions of "aardvark".

Homologous chromosomes work the same way. Chromosome #1 from your Dad will have the same genes on it as Chromosome #1 from your Mom.  The versions, or alleles, of the genes may be different, but the genes will be the same on each of the homologous chromosomes.

What are Alleles?

Different versions of genes are called alleles.

Give me an example:

Pea plants all have flowers that can be different colors.  This is because there are different versions, or alleles, for the gene that determines flower colour. One pea plant may have a combination of alleles that give it pink flowers, while a pea plant with white flowers will have a different combination of alleles.  Some pea plants are very short while others are taller (for the same reason, alleles!).  If it weren't for alleles, we would all look alike (like peas in a pod!).

This page was last updated on 18-Nov-2005 .