what happens to the recessive genes over successive generations? and why?

Question

and why doesnt it disappear from the population??
thanks..

Answer 1

Unless something causes any gene to favourably flourish or die out, the amount of any gene in each generation tends to stay constant.

Let's put it this way: A recessive gene is just one that doesn't show up if you've got a dominant gene. It doesn't go away. And you can still pass it to your children.

Take blue eyes. A recessive trait - only someone with two blue-eyed genes has blue eyes. But some brown-eyed parents have blue-eyed kids if they have the recessive genes themselves.

Answer 2

Ok here's what happens. Genes are located on chromosomes. We have a pair of each chromosome, one from the father, one from the mother. Because of random assortment and a process called crossing over, we tend to get a sort of "mix' or hodge-podge, where the genes are basically randomly distributed. Now, unless there is a reason that some individuals who have a certain gene will die before they have a chance to reproduce, all of the genes are replicated and thrown back into the "mix" in the following generation. You are essentially reshuffling the genes just like a deck of cards.

While the population of humans tends to increase over successive generations, the proportions of each gene (regardless of whether the gene is dominant, recessive, codominant, etc) stays the same. In fact, for two alleles, the Hardy-Weinberg Equilibrium applies:

A^2 +2AB + B^2=1

This formula tells us that the proportion of A and B remains the same (that is why they are equal to the constant 1). You can imagine, for example, that "A" is the dominant allele while B is the recessive allele. The proportion of the recessive phenotype (recall that recessive individuals must have two recessive alleles in order to have a recessive phenotype) is B^2. Since A in this example is dominant, individuals with a dominant phenotype will either be homozygous dominant (i.e. AA) or heterozygous dominant (AB). To find out the proportion of individuals who are dominant, subtract from 1 the value of B^2. (1-B^2).

Now, there are some requirements for Hardy-Weinberg Equilibrium to apply. They are:

1. mutation is not occurring
2. natural selection is not occurring
3. the population is very large
4. members of the population breed
5. mating is random
6. everyone produces the same number of offspring
7. there is no migration in or out of the population

Now, if you get a group of families and see if this applies, it probably won't. We know that people always move around and that mating is not random. So in a small population, over several generations, the gene mix will look different. But when we speak of a HUGE population, everything tends to even out. That is because even though a person might migrate into another place, someone will migrate there to take their place. Imagine this going on at a constant rate.

There are cases where a very small population "lost" certain genes. Recall that I said that there is a sort of shuffling of genes with each generation. Well, we can imagine that sometimes one "gene" won't appear because of pure chance. In a small population it is possible to lose genes- but not in a huge population of millions.

Besides migration there are other events that might change the proportion of a gene. These tend to deal with a non-random event like natural selection. If certain genes give a person an advantage, they might increase in time in a population (over many generations). Mutations are the primary cause of natural selection, because they introduce entirely new genes into the mix. (But 99.99% of all mutations are bad and do not improve "fitness", which is the success in reproducing offspring).

Answer 3

If you have a population where the number of recessive genes (or alleles) is not too high, then the progeny rarely will get both recessive alleles. Only those that do get both recessive experience negative selection, in most cases. All the heterozygous organisms do just fine, and so the recessive allele hangs on another generation. It's only eliminated or selected against in the homozygous recessives.

Answer 4

they lurk.
they don't die out.
for example blue eyes are recessive.

so therefore if you have brown eyes you could be carrying blue.
if you marry a brown eyed person you could actually have a blue eyed child.

now, the flip side of this is that blue eyed people are purely blue eyed and therefore two blue eyed people will have blue eyed children 100% of the time.

So you see, if you want a recessive trait to carry on you need to find mates that express that recessive trait then you can breed true to that recessive trait.

So being recessive may have the oppposite effect from what you thought -being recessive makes it possible to easily select for purity in a particular trait and that means that trait could be less likely to fade away.


this is of course, assuming that being a recessive trait is not also lethal...

Answer 5

They get passed down and can pop up at anytime, those sneaky little things!