How does genetic information pass unchanged from one generation to the next even when a specific trait is not exhibited?

Answer 1

This is a principle of population genetics based on the Hardy-Weinberg Principle.

A trait that is neither selected for nor against will remain in the population at the

same frequency.

In most populations the frequency values can be back calculated from the percentage of the population that is homozygous recessive.

The basic equations are p+q=1

and p (squared) + 2pq + q (squared)=1

The value of q (squared) is the frequency of homozygous recessive individuals in the

population.

So if 20% of the population is homozygous recessive, then q (squared) is .20.

This makes q=.45 (approx.) So, in order to produce a population where 20% of all

individuals are homozygous recessive a full 45% of all the alleles at that gene locus are recessive.

p=.55

p+q=.55+.45=1.0

Now all the numbers for the homozygous dominant and heterozygotes can be calculated.

The approximate percent of the population that is homozygous dominant is 30% with 50% of the population represented by heterozygotes.

.3+.5+.2=1

As the gene frequency for an allele decreases the less likely two individuals that are heterozygous for the trait will be to breed and produce either a homozygous recessive individual or a homozygous dominant.

In the case where a characteristic is dominant and has a low frequency, the trait will be seen in family lines but rarely has the opportunity to be passed beyond a

small population because there is no selection for the characteristic.

An example of this is 6 fingered (polydactyl) individuals, which is a dominant trait.

They exist in the population but they are rarely seen.