Another question on evolution...

Question

Most faulty genes are recessive, which means that unless both parents have the same faulty gene, the mutation cannot be passed on to the offspring, even if it is beneficial right?

So although some species could evolve like that, surely not many would, as it is very highly unlikely for two genes to be mutated in the same way initially, to give birth to mutated young.

Also, how would the first recessive gene be passed on, as the odds of that first mutation occuring in the same generation to two creatures in the same proximity to breed are in the trillions.

Answer 1

There are several aspects of your question which deserve attention: First, even if an animal had only one copy of a gene, it is not the case that it would be unexpressed (truly recessive).  Most genes actually are functional even if present in single copies--but the function may be different (such as a lower expression rate).  Second, a mutation which is really not expressed when present only in a single copy is not selected for or against.  Thus it can persist in for generations until there are large numbers of the gene in the population (this is especially true of small populations).  This is so-called neutral drift.  

So to directly answer your question, two copies of the same mutation do not have to occur in the same generation for a new trait to be introduced.  It might be selected for or against immediately, or it is not expressed, it might persist in the population due to sheer chance.  

Answer 2

Recessive means that two alleles are needed for the phenotype, but the gene can still be passed on easily, otherwise hemophilia wouldn't be a problem.

It only has to be mutated once.  This mutation would then stand a 50/50 shot of being passed on to the next generation.  It may take several generations for an individual to have two copies of this same allele.

The classic Mendelian dominant/recessive gene pattern is actually rare in genetics.  Most are at least partially codominant, so there would be an effect even if heterozygous.

Answer 3

Most gene faults are caused by things other than getting it from your parents.  Genetic damage is caused by radiation (ex skin cancer from sunlight), environmental exposure to mutagenic chemicals (cancer causing chemicals), biological organisms (virus or bacteriological infection) and probably other things we don't know much about.  Genetic mistakes also occur in the process of cellular reproduction, when cells are multiplying by copying genes.  Potentially evolutionary genetic change is occurring all the time, even within your body.  The good news is that by far and away, most genetic mutations do not lead to cancer or some other health problem.  The bad news is that mutations that would lead you to live 1000 years, fly, read minds, or grow a new arm don't happen very often either.  hope this helps  

Answer 4

To take your last paragraph ... it is NOT necessary for the two creatures to get the same mutation in the same generation.

By the very nature of being recessive, it is not expressed (as you correctly point out) unless both parents pass it to the offspring.   But the point you missed is that, if it is not expressed, then natural selection will have no effect on it one way or another.   A recessive allele can survive and spread slowly for *generations* without actually affecting any individuals ... this is known as "genetic drift" and is a VERY important part of evolution.

After many, many generations ... there will be enough descendants of that first ancestor that produced the mutation, that some of these descendants start mating and, for the first time, produce offspring that actually *express* that gene.   If the gene provides some advantage, then this will produce more offspring that have it ... and natural selection is now affecting the propagation of that recessive gene.   If it is really advantageous, then it will eventually spread so that more and more of the population have it ... even to the point of "fixation", where 100% of the population have it.

Answer 5

A novel recessive allele isn't expressed.  It has the same chance of being passed along as the allele is mutated from.  If the parent has enough offspring (and they in turn have offspring), eventually, two with the gene will mate.  Since they will be confined to one region, the effective population will be much smaller.  The extent of population mixing effects the rate.  In a rapidly growing population, recessives are likely to be expressed (founder effect).

Answer 6

A faulty gene can be passed to the next generation easily if it is recessive. A person who has only one copy of the faulty gene is called a carrier. The gene is not expressed. There is no way of knowing that the person has that faulty gene. If you marry such a person, you bring in the faulty gene to your family. If the faulty gene is dominant, the person may not live long enough to reproduce, or people may avoid marrying such a person. The faulty gene will die out quickly.