I have a biology question about inbreeding...sorry to put in GD, but

[mike1963]

the lounge is too frenetic...

And this goes to political issues such as the evolution/creationism debate, stem cell research, marriage laws and related areas...

I'm an engineer, not a biological scientist so I ask this hoping and believing some DUers will know far more than I do.

There seems to be a concensus that 'inbreeding' isn't a good thing. I don't disagree, but here is what I don't "get":

I see, every summer, millions of houseflies. They look identical to me. And we catch fish in the lake I live next to that all appear equally identical.

Of course humans all look just a little bit different, and I'm sure they (we) are genetically distinct as well...which is obviously why DNA 'testing' is considered to be scientific,

but...what is the DIFFERENCE between us and the 'flies' that all look exactly the same? Does every housefly have distinct DNA? I don't understand how this works. Hope this isn't too stupid...it's bothered me for some time.

[leftofthedial]

1. if you were a fly

all flies wouldn't look the same to you

they actually have as much variation as we do.

[Gore1FL]

2. They are distinct

Flies actually mutate/evolve quickly in short time (in part due to their short lifespan). Because of the whole "race" of houseflies is pretty diverse.

I imagine people look pretty similar to flies and fish.

[JackDragna]

3. To answer your question..

The flies you see are not under any sexual selective pressure to look different. Other factors, such as particular flies being able to replicate vibrational patterns with their wings, determine whether another fly will deem the other worthy as a mate. Flies also have a very short lifespan, meaning there's no biological gain to be had in being choosy about appearance. Humans, on the other hand, live a very long time and show many traits about themselves from their physical appearance. Good or bad appearance can tell a potential mate whether an individual is in good health or takes steps to maintain a particular social standing.

Flies do indeed have different DNA. There's simply not much variation in the DNA that codes for appearance because the flies are under no significant selective pressure to be sexually dimorphic.

[mike1963]

5. Okay, I take your point and thank you, but I still have some uncertainty

when I think about, for example, turtles which live in some cases much longer than humans (sticking here to one species at least)...and they really do all APPEAR to be essentially identical. I know you understand my question, I'm not asking it well.

And thanks to the other replies as well. It's hard for me to imagine that a fly would have the ability to distinguish between other flies, but it must be the case. And now that I think about it, I heard as a young man stuff like "all Chinese look alike"...those sorts of nutty things.

Thanks guys

[punpirate]

4. Obviously, the first question you need to ask...

is how carefully have you examined all those flies? Their appearance is identical to you, but only at a distance, and only in their obvious characteristics. Look at human beings from an equivalent distance, thousands of feet up, and they look a lot like the flies you see. Have you counted the number of eye lenses on all those flies, or done chromatic counts of different individual lens colors, or the differences in pheromones that make one fly attractive to another, or counted the number of hairs on each leg of each fly? The pattern of the ribbing on each fly wing?

The other indicator of obvious differences is the number of genes in each specie. Flies have many fewer genes. That means the variations implicit in the total genome will be smaller.

Additionally, there may be (because of the rules implicit in natural selection) many flies with defective genes which you never see--those that never leave a larval stage, or flies which mate but don't conceive, or die almost immediately after the maggot stage because they can't fly or navigate and feed themselves.

Hope that helps. Cheers.

[mike1963]

7. It does help! Thanks, see my post above...

:D

[punpirate]

11. With regard to human inbreeding...

... you might do a quick Google and look for "Gregor Mendel" and read a bit about dominant and recessive genes. That will explain a lot (also explains why our brothers and sisters aren't carbon copies of each other).

[aquart]

6. You're using the wrong examples.

For one thing, because flies and other creatures have pretty involved, evolved structures to AVOID inbreeding.

So do we, actually. Exogamy. Marrying out. Out of the village, out of the clan. Out.

Why? Because closed populations develop little mutations and spread them throughout the community. Most are benign. Some kill. Some do both, like the gene for sickle cell anemia which protects people who have one copy of the gene and brings agony to those who have two (do I have that right?) The best way to avoid the two copy problem is to marry someone who is not your cousin. Or your ethnic background, if you've been tested and know you have a gene for a genetic disease.

[Leprechan29]

9. Sickle cell ex. - Right on

A homozygous recessive genotype (xx) gives the individual sickle cell anemia, while the heterozygous genotype (Xx) gives resistance to malaria. Thats what you were describing I think

[Leprechan29]

8. The Problem with Inbreeding (A Short review)

Inbreeding tends to magnify certain traits (Hemophilia being one - I think thats its name), as is shown with many royal families on the European continent. Inbreeding uses a limited genetic pool, and thus a recessive trait has a much better likelyhood of being expressed (ie homozygous recessive - qq as opposed to QQ or Qq). This is a major problem if the recessive trait codes for a health problem. Additionally, if the gene pool is limited, then the varitation in offspring is different, and if a disease goes through this population due to a genetic weakness, the chance of a few survivors due to genetic luck is vastly decreased.

An odd situation was proposed to though: If life were wiped off the earth except for a few individuals, inbreeding would actually be a benefit - dont ask me for the logic behind that, because I have forgotten it in the past 3 or so months, but there is some reason...

[Fear]

10. interesting topic, and very important - diversity

Just to give you this. You can be for 100% sure that nature's selective system works. Only the strong will survive, and only the strong will breed and lay eggs......ofcourse there are some weaker variants of 'flies' for example, but since they are weaker, they enter the 'circle of life' and they become pray for birds or just die faster cause of our environment - which straight away looses all inbreeds cause they do not have the power.

Also take for fact that every single fly you see is different and has it's own uniqueness. When people move around and bring flies from another continent you could have introduced a new TYPE of flies which (perhaps bringing a disease with them) could reign over other flies for being more effective / better survival skills and perhaps when mixing in with local flies providing a new breed of flies with different skills and techniques.

Diversity in nature is the key to it's existence. With diversity you have different kinds / and breeds. When one / more diseases would spread the lands, there will be (not in all cases) groups of animals / insects whatever that will survive the disease for being imuum yet another group will die for belonging to another group vulnarable to the disease. So diversity is natures way of surviving against diseases and other forms of disasters.

For example with humans. Aids is a disease spreading around rapidly. Yet there ARE people who are imuum to the disease. They are capable of living with the disease but not being affected by it because of a GENE in their DNA. And so we carry many other diseases (remember all of these shots you got when you where a baby) that are floating around in our bodies yet we are imuum to them.

During the middle ages there was a strong selection going on with some strong diseases where only a few where imuum to.

So this brings it back to genetically modified crops / plants and animals.......either by cloning or some other way. We create an *in our eyes* strong plant / animal, without any diversity......they are all the same.

So let's say we export and grow only rice plants from one kind in China - cause it's a strong plant, grows fast etc. etc. That means it would also only take ONE disease to destroy the WHOLE crop.

Diseases mutate and develop themselves as well and are fast adapters of the environment.

So ultimately, by cloning we put ourselves in the dangerous position of loosing EVERYTHING because of one error somewhere....meaning a disease would be able to attack a certain area.

The way diversity is setup is that it will sacrifice a group (weak) but allows a stronger group (imuum) to survive and continues on.

on edit:
do a search on terminator seeds by monsanto
http://www.ethicalinvesting.com/monsanto/terminator.shtml
there;s much more about this, which explains everything much better then I did here

[lapauvre]

12. I don't know a damned thing

about this, but I am so proud to be among those who do. Great post.

Posts, actually.

[Guy_Montag]

13. Trivia moment - sorry

There is more genetic diversity in a single tribe of Chimpanzees than there is in the whole human race. That is to say that the DNA in the tribe has more differences than the DNA in all humanity.

At some point we went through a population bottleneck where there were very few individuals.

Sorry no reference. I remember pointless facts, not where they came from. As a guess "Almost Like a Whale" by Steve Jones (I think).