Do genes need to exist within the host body of a lifeform until it’s death to gain the information they hold? Or does the gene know everything it will pass on pretty much right after conception?
If it’s actually a combination of the two, then it can be expressed as a ratio. I’d like to believe that ratio should be kept as wide as possible if you have evolution in mind.
Your DNA is formed by the combination of chromosomes from your two parents and stays the same over your lifetime. Occasionally random mutations may occur in your body, and occasionally these can cause cancerous growths. But your genes in general don’t ever change.
If DNA carries behavioral habits (like the desire to be more violent, sensitive, loving…), then it must be able to change naturally.
Or are bad habits passed by something other than genes?
Genes don’t gain knowledge. Genes are a pattern of chemical structure. Your specific genes are mostly set upon conception, when the two contributing pieces from your parents come together. Random mutation may occur during the copying, and in that early stage that would be significant, but as the embryo develops, that becomes less a factor. Later random mutations may become tumors in those specific cells without affecting the rest of your genetic structure.
What decides your children begins with the sex cells. When those cells begin to form, they divide your regular genetic contribution in half. Your chromosomes have two halves, and this splitting puts one half of each chromosome in each reproductive cell. During this process, some errors in the division are possible that will scramble the genes that your children will have. But those strange splits would only occur in each cell individually, so not likely to happen the same in multiple cells. So it only affects your offspring if the reproductive cell that gets that weird split is the one that forms the embryo. This makes the likelihood pretty low.
Your children’s genetic structure is then determined when half of your genes join with half of the other parent’s genes.
friedo, as I understand it, one’s DNA actually changes all the time, to the extent that most cells in your body have slightly different genetic profiles (if you were to sequence the whole lot of them).
However, these tiny mutations generally don’t make a functional difference - often they will be somewhere in a non-coding region, or they may be silent mutations which don’t affect the structure or function of a protein.
Of course, in an evolutionary sense, the mutations that matter are the ones which occur in your germ cells (spermatozoa for men, ooctyes for women). AFAIK, spontaneous mutation goes on in the process of spermatogenesis/oogenesis just as it does in somatic (non-germ) cells. Again, most of these mutations are silent, and will be passed along to the next generation without anyone ever knowing. Some of them are lethal, and will result either in death of the cell, or in death of the embryo early on in development. A small proportion are functional, and will result in phenotypic differences (ie different characteristics) in the resulting offspring.
Genes hold all the information they ‘need’ straight after conception. But they don’t stay the same throughout the organism’s lifetime. Mutation is an important evolutionary force.
Disclaimer - this is my understanding of criminalcatalog’s question, and though I’ve done a fair bit of study in this area I’m not up-to-date in the latest genetic theory, and I don’t have time to check up my textbooks. If anyone is better informed, please correct any misapprehensions in the above.
Sorry. Every behavioral action is a choice made by the actor. Desires are neurochemical events, and while a person’s DNA may predispose the person to certain specific neurochemical events, the transition from neurochemical event to behavioral action is based in volition. The choices made by the person in response to a neurochemical event may be influenced by the person’s conditioning, but the conditioning itself is not genetic.
Bad habits, violence, lovingness (?), sensitivity, etc are not hereditary, or at least not to any significant extent. There is no single gene or combination of genes that will cause someone to be violent. There may, however, be a gene(s) that might predispose someone to be more “Sensitive” to a violent environment, and to act upon the violence that they are exposed to. By this, I mean that there might be a genetic component that is altered/missing, in which the protein for which it codes doesn’t have the effect it should have, thus “deregulating” a chemical response to a stimulus, so that the person in question responds differently than expected (i.e. more violent).
IIRC this is a theory about smokers/drinkers/other addicts - there is a substance called dopmamine which is partly (and only partly) responsible for the regulation of pleasure/joy senstations in the brain. Some addicts to various substances (I have no numbers handy, and this is such a generalised theory that any that I gave would be useless) appear to have less, or malfunctioning dopamine in their systems, and so it takes a larger stimulus (a larger amount of “joy-producing sunbstance”) before they “feel the same amount of pleasure” as a “normal” person. HOWEVER - the genetic factor that leads to this lowered dopamine activity DOES NOT NECESSARILY MEAN than the person will become addicted to something. That is a product of the environment that the person is experiencing.
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A person is genetics multiplied by environment, but environment is SO MUCH BIGGER than the genetic component.
Some things are fixed by your genes, however, such as your eye colour, or birth marks. Even things like height can vary - if you are malnourished, it is doubtful that you would be as tall as if you weren’t. Genes, for the most part, simple provide the POTENTIAL for the traits of a human. A large part of their function is at the cellular level, regulating respiration, or the digestion or food, etc but once you start getting to multicellular characteristics, environment matters a whole lot more.
No one is sure exactly what causes certain behaviours. Most people believe it is a combination of genetic traits and experiences and knowledge gained during the person’s lifetime. Identical twins seperated at birth will have many things in common and many differences, due to their different life experiences, for example. But their DNA is the same.
But DNA predisposes, as you said. That is what I’m talking about. What does one DNA string reproduce in it’s mutual cooperation with the other DNA string, restricted to personality traits, quirks, talents…
tritone , your reply is what I’m referring to is closest to the answer I need, but not quite. I’m not sure the original question is worded well enough
No, I said DNA is a factor in behavioral disposition. Nobody yet understands the relationship that genetics have to how people act. It is demonstrably provable, however, that genetics are not the only factor. It is also known that your DNA does not “learn” or “retain knowledge” of any sort during your lifetime.
criminalcatalog, when I said that DNA changes, I didn’t mean in any way to imply that DNA changes according to the behaviour or environment of the organism (OK, strictly speaking, some environmental factors might --> a higer rate of mutation, but that’s not what we’re talking about here). Changes in DNA are random, and don’t relate to “learning” or gaining any “new information”.
As for genes and behaviour, the link between them is very tenuous at the moment, as people have said above. We can find various genetic factors which might predispose to certain behaviours, but these traits are multifactorial in origin, and likely to relate more to environment.
For example, if my mum and dad both smoke, I’m more likely to be a smoker, not because they have passed on their “smoker genes”, but because I’ve been brought up to think that smoking is an ok thing to do. If I decide not to smoke, despite the fact that both of my parents do, my genes don’t change to reflect the fact.
The random changes to DNA that tritone mentioned are called mutations. They can happen when DNA is damaged by radiation or chemicals. There is no physical mechanism whereby experiences are ‘written’ into the genome. Likewise there’s no evidence of the sort of elaborate biological programming that would have to exist in order to decide exactly what it is that must be written in order to produce a desired change in inherited traits.
There are at least a couple of cases of non-DNA based inheritance that do involve passing on acquired traits:
•IIRC there’s a type of barnacle, or small sea beastie, that reproduces in such a way that the tooth-shape of the parent is physically imprinted on the tooth-shape of the offspring.
•Herbicide resistance in some plants is passed on not through DNA, but by an irreversible change in the membrane structure of subcellular organelles.
Neither of those sound like the sort of thing an organism would get up to if there were already a more sophisticated DNA modification system in place.
Of course if someone claims that the plants and barnacles are too primitive to have the DNA modification system, then there exists some creature which is the most primitive that has the system. If there is such a thing, the necessary difference between it and it’s predecessors is invisible to science.