Discussion of all aspects of cellular structure, physiology and communication.
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Normally, we think of individuals competing for the chance to pass on their chromosomes, but what about competition between an individual's chromosomes? Suppose the Y-chromosome could change sperm such that Y-carying sperm out-do X-carrying sperm. Even if the Y-mutation reduces the individual's fitness by making his sperm generally less effective, it could make up for this by increasing its own odds relative to the X-chromosome. If the Y-mutation makes my genes have a 10% reduced chance of being passed on, but it gives my Y-chromosome a 75% and my X-chromosome a 25% chance, the Y-mutation is more likely to be passed on.
normal: 1.00 × 0.500 = 0.500
mutant: 0.900 × 0.750 = 0.675.
0.675 ÷ 0.500 = 1.35
In comparison to the normal variation, my mutation has a 35% higher chance of being passed on.
So, are there any observations that sugget our chromosomes are in competition with one another?
The genes required for survival is distribuited in all chromosomes, one over the other will result in imbalance.
A single chromosome can exist more, as long as it does not affect the other chromosomes or cellular process like mitosis.
Rarely is the case as your example.
If Y chromosome want to out run a X chromososme sperm, there will be more males and less females.
Over all reduction in number of females will affect survival of fittest.
In worst case scenario, there will be no more females to mate with and the species cease to exist.
Funny, some men claim that they give only male offsprings! "a pure co-incidence".
It is like engine runs the wheels and runs along with the car. if only engine or wheels run alone, the "car" will be left behind.
Wow, ur discussion is really insightful! It makes me wonder, in alleles, what makes one dominant and the other recessive? Why is the transcription of the chromosome that carries the dominant gene preferrable to the one that carries the recessive gene?
In contribution to ur topic, it is said that the x-sperm cell is faster than the y-sperm cell, so that whether y or x chromosome fertilizes the egg depends on the time of copulation with respect to ovulation.
*when the facts change, I change my mind*
1. dominant vs. recessive.
let us consider a 100 amino acid protein which gives green color to the beans. no matter what if there is a single protein gives green color to the seed, say a bean like green peas.
Suddenly a mutation happens, 100 amino acid protein is converted, or stopped in the middle, thereby converting it to a 50 amino acid protein. this protein is not functional.
dominant gene express itself no matter the concentration of recessive genes.
let us consider a homozygous ( two same allele) green parent mating with a homozygous (two same allele) yellow mother.
the offspring is always green. because green in always dominant.
The default color of the offspring is yellow. if there are no transcripts, then seeds will get yellow color. even if there is a single green transcript, the color will be green. because green express as a functional protein while the yellow is not a product of a transcript but the lack of green.
Philosophically, lack of light is darkness. light is dominant while yellow is darkness. lack of a single transcript of green protein will result in darkness a.k.a yellow color.
As far as here, I think you are just testing my knowledge on classical genetics, So getting to the real question
Yes the sperm will fertilize a egg faster.
if that is a advantage to the species which makes the chromosome survive ?
Technically, dominant/recessive is an observation of phenotype that doesn't take into account the pathway from genotype to phenotype, thus there are different ways to achieve a dominant/recessive relationship. The simplest mechanism I can think of is that the dominant gene codes for a functional polypeptide, while the recessive gene codes for an afunctional one. (see loss of function mutation) There may be other mechanisms resulting in dominant/recessive relationships that I'm not aware of. Also note that I'm using the term "function" loosely such that it includes adaptive and maladptive "functions".
Well, as I demonstrated, a genetic variation might be able to benefit itself without benefiting the individual. Furthermore, it's always possible for a trait that benefits individuals to ultimately harm the group or even the whole species (see group selection).
Selfishness and uninhibited reproduction both seem like traits that would benefit the individual, but a group full of such people would be a maladapted group. They would all be back-stabbers, and they would create more offspring than they can feed and nurture. What I'm suggesting above is similar. Normally, it's the beneficial traits that are selected for, but I am proposing a mechanism by which a harmful trait could be selected for. But in this case, the conflict is between gene and individual, not individual and group. For example, IF a Y-mutation made meiosis II impossible with an X-chromosome present, without causing severe drawbacks on the overall process of meiosis or the health of the individual, that Y-mutation would be selected for. It would be selected for despite the fact that it reduces individual fitness.
My questions are: Can such a mutation arise? Has such a mutation arisen? What happens after such a mutation arises?
As for the end of the species, I don't think that follows. If all the other guys are only producing male offspring, but you're the lucky guy that can produce female offspring, that would be a huge boon to your genes.
Hi guys thanks for ur replies! I think one of the reasons for dominance in traits is that d dominant gene tends to inhibit the expression of the recessive gene either directly or through a corporative protein.
*when the facts change, I change my mind*
What do you mean by "inhibit the expression of the recessive gene"? I would find it hard to believe that, of all the potential inhibitors, a protein should be inhibited by a mutant version of itself.
On the other hand, you might be talking about a situation in which the protein has the function of inhibiting some other gene's expression. In that case, the recessive allele is still coding for an under-performing protein product. But since the protein's job is to serve as an inhibitor (perhaps a negative feedback inhibitor), its hypo-activity results in the hyper-activity of another protein.
Actually, there could be a pathway between the dominant and recessive protein products. I will speculate about how such a pathway might arise.
Suppose there are two versions of the allele that are initially codominant. I will call their protein products "A" and "B". A and B are beneficial on their own, but they interfere with eachother in heterozygotes, so heterozygotes are less fit than homozygotes. Since natural selection can only select against alleles, not genotypes, the heterozygous genotype persists.
Then, in comes a new gene from somewhere else in the genome. It produces protein product "C". Suppose that, by coincidence, C forms a negative feedback inhibition pathway between A and B. The gene for C will be beneficial because it makes sure that A and B aren't being produced at the same time. In that way, one acts as dominant to the other as long as C is working.
Maybe it could happen...
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