Law of Independent Assortment....

[sps27]

The paragraph says 'the order and spacing of genes on a chromosome can be determined from the frequency with which the different gene pairs recombine. Genes that are far apart will recombine more frequently that genes that are closer together.

And then down below it also says "Note the location of the genes for plant height and pod shape. Those two genes are quite close to one another and therefore should not assort independently"

Are these two statements essentially contradicting each other? The genes that are closer together on a chromosome, will not assort independently, meaning there is a higher chance for recombination. But the genes that are further apart also recombine more frequently. Any thoughts?

---

Members don't see this ad.

 

[Schenker]

I think you may misunderstand the term recombination. When we say that a gene pair recombines, we don't mean that the alleles reassume their original combination. Gene recombination is actually the opposite. Gene recombination is when the alleles assume a new combination.

Let's do a quick example. Let's look at gene A and gene B on chromosome 1 in Bob, Lisa, and their child. They each have two copies of this chromosome.

Bob: AB and AB
Lisa: ab and AB
child: Ab and AB

One of the child's chromosome is Ab, a combination of alleles not found on any of her parent's chromosomes. The genes have recombined.

 

[sps27]

I think you may misunderstand the term recombination. When we say that a gene pair recombines, we don't mean that the alleles reassume their original combination. Gene recombination is actually the opposite. Gene recombination is when the alleles assume a new combination.

Let's do a quick example. Let's look at gene A and gene B on chromosome 1 in Bob, Lisa, and their child. They each have two copies of this chromosome.

Bob: AB and AB
Lisa: ab and AB
child: Ab and AB

One of the child's chromosome is Ab, a combination of alleles not found on any of her parent's chromosomes. The genes have recombined.

Thanks I appreciate it. I understand what you have stated, i.e., the allele's one coming from each parent. I was thinking more on the lines of 'linked' and 'unlinked' allele's on a single chromosome, and how and why that happens. If two allele's for a trait are on separate chromosomes, they will not be linked and will assort independently during meiosis.

The first line in my original post I think is referring to cross linking that happens in meiosis. That is, if the allele's are located further apart on a single chromosome, their is a greater chance of recombination during cross linking in meiosis. The second line is alluding if the allele's are closer together on a single chromosome, they might be linked (not assort independently as stated by law of independent assortment) and will stick together and furthermore the trait exhibited by linked allele's will not be a 'true' representation of that trait. Is this understanding correct?

 

[Schenker]

If two allele's for a trait are on separate chromosomes, they will not be linked and will assort independently during meiosis.

The first line in my original post I think is referring to cross linking that happens in meiosis. That is, if the allele's are located further apart on a single chromosome, their is a greater chance of recombination during cross linking in meiosis. The second line is alluding if the allele's are closer together on a single chromosome, they might be linked (not assort independently as stated by law of independent assortment) and will stick together

Yes, this is correct.

In other words, if two genes are on the same chromosome, they will not recombine frequently if they are close together and will recombine frequently if they are farther apart. They will recombine more frequently the farther apart they are (up until a point).

I hope this clears the confusion you had in your first post:

Are these two statements essentially contradicting each other? The genes that are closer together on a chromosome, will not assort independently, meaning there is a higher (this should say lower) chance for recombination. But the genes that are further apart also recombine more frequently. Any thoughts?

 

[sps27]

Yes, this is correct.

In other words, if two genes are on the same chromosome, they will not recombine frequently if they are close together and will recombine frequently if they are farther apart. They will recombine more frequently the farther apart they are (up until a point).

I hope this clears the confusion you had in your first post:

Yes it does, thank you. I hit the panic button too soon. Should have read the full chapter first. Thank you though.....

 

[PreMedRookie]

chromosomes can "break" and "recombine" at any spot along the chromosome.

The further away the two genes are, the higher the chance there is that it will "break" between them, and hence, recombine.

However, if the two genes are right next to each other, the chances that the chromosome will "break" in the small space between them is less.