Re: Percentage values commonly given for differences in DNA etc, may be meaningless.

Jane Andrews (
Wed, 31 Jul 1996 12:32:24 +0100

On Tue, 30 Jul 1996, Richard Foy wrote:

> Is it possible to estimate the number of base pairs involved in
> determining various physical characteristic, i.e. physical height,
> hair color, wavyness or length, etc?

Not really. Very few characteristics are determined by a single gene,
most such as the ones you mention rely on a number of genes. The height
of pea plant as demonstrated by mendle's famous experiments is determined
by a single gene locus at which there are two possible alleles, so the
plant can be either tall or short. Human height however is a polygenic
trait involving the interactions and additive effects of a number of
genes. In addition to this environmental effects have enormous impact on
something like stature. As I hope this demonstrates, the genetic basis of
visible characteristics is more complex than a simple one gene-one trait
model. Many genes have not been identified and the interactions between
genes are not understood. Therefore it's not possible to answer your

> In other words what is the minimum number of base pairs that makes
> observable difference in physical characteristics?
Well, in some ways this is quite easy to answer. In some cases, such as
sickle cell anaemia, a phenotypically obvious trait, in this case a
disease, can be brought about by a single point mutation; only one base
pair needs to change.
On the other hand, large sections of our DNA compliment is non-coding and
so many mutations can occur with no noticable affect.

Jane Andrews.