Is it possible for a recessive gene to become more and more dominant over a long period of time?

Question

Is it possible for a recessive gene to become more and more dominant over a long period of time?

Answer 1

First, it's really important to understand that a gene, by itself, is not 'dominant' or 'recessive'.    It is always 'dominant' or recessive' *with respect to another gene.*

Second, (just so we're being accurate), it is not genes that are dominant or recessive, but *alleles*.    

E.g. If there is a *gene* for 'eye color', then 'blue eyes', 'brown eyes', 'green eyes' are three different *alleles* for that gene.  And green eyes may be dominant w.r.t. blue eyes, but recessive w.r.t. brown eyes.  (I say 'may be' in this paragraph because in the case of eye color it's not as simple as a single allele of a single gene.)

So with that said, yes it is possible that an allele A may be recessive w.r.t. allele B, but if if is much more *beneficial* than B, then once it starts getting expressed in individuals who get a double-dose of A (what we call 'homozygous'), then it can increase in frequency in the population while B decreases ... until B disappears completely (0% of the population have it).  But A may be *dominant* with respect to another allele C.

So in a sense the population has gone from a small number with *recessive* allele A (with respect to B), to a large percentage with *dominant* allele A (with respect to C).

Answer 2

no, not unless by a direct mutation a new allele is introduced that is dominant. recessive genes just get expressed more over time but only if consanguinous matings are frequent, and there would be more homozygotes. if not, they are masked by dominant alleles and the allele frequency stays pretty much constant, unless all the dominant homozygotes get killed for some reason ( eg if having the recessive trait was an evolutionary advantage) and naturl selection works in favour of the recessive allele's favour.

Answer 3

A recessive gene does not become dominant.  It can become more prevalent.  (I think that's the word you wanted.)

If an animals diet is rich in a nutrient (e.g. vitamin C), it may lose the trait.  An enzyme to synthesize vitamin C will be dominant to the defective or unexpressed enzyme.  Losing the enzyme takes away a metabolic burden, so those with the recessive trait have an advantage.

Answer 4

Do you mean within an individual?  Or within a species?

In general the answer is no in either case.  However, with trinucleotide repeat expansions it is possible if you're thinking of the long period of time being a few generations.