How is the concept of crossing over and its frequency related to where a gene is located?

Answer 1

I think your question is really about why some genes travel together, and their high cross over rates are always associated with other alleles in close proximity.

(I hope your not looking for a mathematical frequency rate, because that can be complicated, and I will leave that to other more experienced people here, if that's the case.)

But in general, genes are moved during cross over events by blocks of DNA, not by genes.

So, if I imagine a gene as a "house" on a street with other houses, the "house" doesn't cross over to the other side of the street, but the whole "block" crosses over to the other side of the street.

That particular house (or "gene", to reverse the example) moves with the whole block of houses.

genes cross over in terms of its neighbors.

There is probably a specific sequence recognition "splicing site" for crossing over that says "start here, take all of this, and then stop here".

No one knows how this sequence is "spelled out" yet.

That is my take on your question.

Pass on the good Karma!

Answer 2

Genes that are close together on chromosomes are said to be linked. Why is this? Let me try to explain. Crossing over starts off at a certain point on a chromsome, and as a result, all the DNA between that point and the end of a chromsome will be exchanged with the same DNA from the other copy of the same chromosome.

If these are our two sister chromatids (2 copies of the same chromosome, one is from your mother, one is from your father). Lets say each letter represents a gene:

x
x
x
x
x
x

l
l
l
l
l
l


Now, if they cross over at the 2nd gene from the bottom, the following chromosomes would result:

x
x
x
x
l
l

and

l
l
l
l
x
x

So, basically, the chromosomes exchanged 2 genes, they are the same genes, just different alleles (copies) of the same gene. Now, linked genes are said to be linked because they need to be together, and can't be separated. If two genes are far apart on a chromosome, the chance of them being separated by the mechanism I just showed you is much greater than if they are close together. This is simply by chance, that the crossing over site would occur in between the 2 genes. If two genes are right next to each other, they can be considered linked because the odds of crossing over occurring RIGHT BETWEEN THEM is much less than the odds of crossing over would be if they were far apart. This is simply by chance becuase there are more places for crossing over to occur.

So in summary, genes that are closer together are less likely to be separated by crossing over than genes that are further apart.

Answer 3

crossing over is the exchange/swapping of genes of 2 pairs of homologous chromosomes at the same locus.
the locus is where the allele is located.
an allele is a different variation of a gene.
for example, the gene that controls eye color is found at the same specific part of each homologous pair; the allele for one gene of one chromosome could be blue, the one found on the other chromosome could be green and then they'll swap during crossing over.
about the frequency...im not quite sure if there is a specific number of times. but i dont think there is.

the main thing here is that only different alleles of the same genes cross over and they are found on the same locus.

Answer 4

crossing over is the actual relocation of a gene or genes on chromosomes. it can cause different phenotypes and mutations.