A Lesson in Basic Genetics

[paulh]

Hi, I just finished reading your thread and I have to say it really is awesome and has taught me A LOT but there is one thing that I'm not sure is correct. Ok so I'm confused by the 2 strands of DNA you use to represent each morph. Wouldn't it be better to represent the DNA for each morph as a helix instead of 2 strands? I thought that DNA was a helix and if it is then i'm not sure if your illustration is correct. The reason I say this is because if you combine the 2 strands the way you visualized them then it won't create a regular DNA helix. Realistically one strand would only have one gene per allele, it is only when you combine the other strand that you get the second parent gene which forms the helix. With your illustration it looks like you are trying to represent one strand as an entire DNA helix because you have the 2 gene dots which would only happen with a fully formed helix. Idk if I'm right about all this or if i'm just totally confused. Anyways, I would appreciate if you got back to me on it just so I can make sure I'm understanding the basics correctly. Thanks again for the awesome guide.

-Sean

You are right; that illustration is not correct. IMO, this is less pretty but more correct.

Pair of homologous chromosomes
-o-o-A-o-o-o-B-o-o-o- = the double helix of DNA in one chromosome. Each o represents a gene.

-o-o-a-o-o-o-b-o-o-o- = the double helix of DNA in the other chromosome. Each o represents a gene.

By the way, alleles have different DNA sequences but the same location in a chromosome. In my pair of chromosomes, A and a are alleles because they have the same location. B and b are also alleles. A and b are not alleles, and neither are a and B. A, a, B, and b are all genes.

Link: http://ghr.nlm.nih.gov/handbook
The link is to the Genetics Home Reference, which can be freely downloaded. The first chapter has material about genes and chromosomes and DNA. It may be helpful. By the way, the Home Reference shows a chromosome as X-shaped because that is the stage that is visible. Each X-shaped chromosome is dividing and will eventually become 2 rod-shaped chromosomes before unwinding into an invisible thread.