A question about evolution

Imparcticle

According to evolutionary theory, an animal goes through physical changes according to genetic mutations that occur, which in turn are influenced (is the influence direct or indirect?) by environmental changes.
When a genetic mutations occur in humans for example, the result is a handicapped human right? I am assuming this is the same for other animals as well. So if this is true, then wouldn't the genetic mutations that occur in an animal (as a result of environmental changes) cause a handicap to occur in the animal's body?

iansmith

Not all mutations are bad, some are good. Mutation migth gave the individual an handicap but if the handicap has advantages it will be selected for. A good example is sickle-cell anemia and malaria. A mutation in one of the RBC cause the RBC to curve under low-oxygen tension. and it cannot transport oxygen. Homozygous and heterozygous individuals are both affected. The homozygous will die due to its condition but the heterozygous will surive because a certain percentage of its RBC function normally. The heterozygous will also have an increase survival rate to malaria compare to individuals will no RBC defect.

Another example would be the possible mutation in a jaw muscle. The muscle is not present in human but it is in other primate. This muscle give a powerful jaw but migth restrict the development of the cranial bone. This mutation has been suggested to be the initial step that improve our brain power.

selfAdjoint

Lots of mutations are neutral. Probably our genetic transcription systems have evolved to be fairly robust under common switches of g for c and so on.

Chrono

Kind of like the finches during El Nino, right?

Jon

Phobos

In everyday speech, the word "mutation" has a negative connotation. But genetically speaking, it's a change in the genetic code (e.g., altered or incorrectly copied segment of DNA). If the change occurs in an important gene (i.e., one that is currently expressed and is critical to the creature's life), then yes, it will probably be harmful. Many times, mutations can be neutral (no effect) such as a change to un-expressed portions of DNA or to some characteristic that is not critical for the creature's life and reproduction. On rare occasion, you may get a beneficial mutation.

Couple more good examples....
(1) Bacteria reproduce fast & there's lots of opportunity for mutations. When we attack them with a new antibiotic, many will die off but some with a fortunate (for them) mutation will survive. Until we applied the antibiotic, the mutation was neutral because the environmental conditions didn't discriminate between mutated and non-mutated.
(2) In Richard Dawkin's book Climbing Mount Improbable, he gives an example of some kind of insect with x body segments (sorry, I forget the details at the moment). During its development from an egg, its genes tell it how many segments to grow (something like "make this body segment x times, each time with two legs"). With enough segments, you get something like a centipede. A mutation may cause the genes to send the grow-segment command an extra time. Note that the mutation was a modification of an existing ability, not the formation of a whole new ability. So now it has a perfectly working extra body segment. A centipede with 10 body segments might not notice an extra one. Or that extra body length and mass might just give it the little extra it needs to out-compete its rivals.

russ_watters

My little toenails are round and grow straight up. Seriously. Yeah, I'm a freak.

Jikx

wow.. you too?

Actually, it seems like my two littlest toes have no joint in the middle like the rest of them :o

Imparcticle

me too!

back to the subject here....
I have gained much insight here. How do those "neutral" genetic codes get "activated"? Is it if and only when they're inherited?

Monique

A mutation just happens in a single cell, so the mutation must have happened in a germline cell (spermatozoa, oocytes) in order for it to become present of the whole body or it must happen in the first celdivisions after fertilization.

There are instances that mutations in a single cell can have a phenotype, think for instance about a mutation in growth regulation or cell death genes, which can cause cancerous overgrowth of that single cell.

benjaman

Would it not be wonderful if mutations are not random but purposful as the DNA has been touched by new environmental demands?

Just like adaptive mutations seen in hungry E. Coli.

See http://newsinfo.iu.edu/news/page/normal/1160.html .

FZ+

Er... what? I am sorry, but mutations simple do not work in a purposeful way. Lysenkoism is simply wrong. The adaptive mutation linked to is just a matter of increasing the rate of mutation when under stress. It is still very much random.

iansmith

Not all mutations are random, in bacteria there is hot spot for mutation and under a given conditions a specific mutation migth selected. It is sometimes refered to as phase variation. Usuallly these hot spot are reapeats of nucleotides or polynucleotides tract
http://www.sciencedirect.com/science...3ad0fdb37dd6b0
http://www.pubmedcentral.nih.gov/art...medid=11983903
http://jb.asm.org/cgi/content/full/1...&pmid=14617664
http://iai.asm.org/cgi/content/full/...&pmid=10858226
http://www.pubmedcentral.nih.gov/art...bmedid=8855319

Phobos

Even in larger organisms, some mutations are more probable than others even if randomness is still there.

Monique

There sure are hotspots for mutions, but whether they are meant to be there.. ? You'd think so but I don't think the mechanism is fully understood yet.

benjaman

How much do we understand about chromosomal allocation/recombination in meiosis? Is it believed to be a purely random process? Or is it a highly regulated complex process?