Can the process of crossing over in meiosis produce new alleles?

Question

One expert (A&P teacher) that I spoke with said she didn't think so, but couldn't explain why.

I was told that during crossing over a chromosome breaks and the disconnected part switches with the other chromosome. If the break happens in the middle of a gene and they have different alleles it seems this could produce a new allele. What have I gotten wrong?

Answer 1

You are correct and you teacher is not.

An allele is a variant form of a gene. Alleles can produce visible or biochemically detectable phenotypes in the individual. An individual who is heterozygous for two different mutant alleles at a given gene could have a recombination event (by breakage and rejoining during metaphase I of meiosis) between the two mutant sites. This would produce a wild type allele (nonmutant) and a doubly mutated allele. The doubly mutated allele typically produces a nonfunctional gene product but in some cases a second mutation produces suppression of the original mutation (or even a novel phenotype) by virtue of the way the mutant sites relate to each other in the folded protein.

The closer two mutations are the less likely recombination is to occur. In fact the observed frequency between two mutant alleles is the basis for genetic mapping studies. Good job thinking this one through.

Answer 2

No. Crossing over puts the alleles on a different chromosome, but the alleles do not change.

For instance, if the dominant alleles for three trait are on one chromosome, and the recessive for the same three traits are on the other, crossing over may switch one dominant and recessive at an end of the chromosomes while the other two at the opposite end are not affected.

Answer 3

thats not possible....the alleles are already there, they are different forms of the same gene, u cannot create new forms of a gene during crossing over, u just create different combinations of different alleles together. Meiosis only provides variability by creating mixtures during chiasmata and independant assortment, but there are no new alleles created.

Answer 4

linked genes are usually genes that are close together. That means when crossing over occurs, they will be inherited together. Genes that are far apart are unlinked. That means that it is unlikely that both genes will cross over. It is more likely that these genes will become split up. homologous chromosomes carry the same genes but not the same alleles. So one homologous can code for blue eyes and the other brown.

Answer 5

Dizz has the right answer: if one copy has the sequence
AAACGCTG and the second AGACGCCG they are two alleles, If crossing over occurs between the middle CG, then you will have AAACCCCG and AGACGCTG. Both of these are new sequences, and therefore new alleles.

Ignore PIPI B's answer: crossing over can occur anywhere within or between genes

Answer 6

Crossing-over takes place in diplotene of prophase I in Meiosis I. When the allele is exchanged, the whole allele is exchanged. It does not exchange part of the allele and keeps part of it. So, there is no way, a new allele can be formed.

Even under insertion and deletion, it is the whole allele that is being inserted or deleted and not like things like transposon that takes part of the gene.

Bottomline, there is NO way crossing-over gives you new alleles.

Answer 7

arghh i just type a long answer for this then i lost it all =(

ok the basic concepts was that crossing over is just the recombination of genes. therefore crossing over is just the swap of genes from the father and genes from the mother
eg
. say one strand from your father has the genes coding for blue eyes and a big nose

and the strand from your mother had the genes coding for brown eyes and a small nose..

then the cross over of these two strands at the eye colour loci (at the position on the chromosome for where the genes coding for eyecolour are) would produce a strand with blue eyes and a small nose and a strand with the genes for brown eyes and big nose...(notice the swap of genes on strand)

hence a baby could be born with his mother's brown eyes and his father's big nose.

well this is confusing and seen as though i lost my first answer i typed to this question doesnt really help but i hope the links below will help