Can independent assortment occur on the same chromosome?

[DingDongD]

Let's say that two genes were far away on the same chromosome, can can independent assortment still occur? Or would it be classified as linked?

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[whitepatchMD]

I think your understanding of independent assortment is incorrect. Mendel's Second law states that the segregation of the alleles of one allelic pair is independent of the segregation of the alleles of another allelic pair. Mendel showed this with his back crosses with the F1 generation to the recessive parent. E.G. when looking at peas it means that the alleles for seed color assort themselves on the metaphase plate independent of alleles of round vs smooth seed shape. I hope this helps

 

[krukshanks]

I think your understanding of independent assortment is incorrect. Mendel's Second law states that the segregation of the alleles of one allelic pair is independent of the segregation of the alleles of another allelic pair. Mendel showed this with his back crosses with the F1 generation to the recessive parent. E.G. when looking at peas it means that the alleles for seed color assort themselves on the metaphase plate independent of alleles of round vs smooth seed shape. I hope this helps

He didn't misunderstand the concept. I believe what he is asking is: "If the allele pair that controls seed color and the allele pair that controls round vs. smooth are on the same chromosome pair but are very far apart and thus almost always get switched around during cross-over, will that be classified as independent assortment?"

The way I was taught in class was that although the probability of those two genes get switched around is very high, it is still possible that they stay on their own chromosome. They are thus not classified as independent assortment, although their behavior is approximately independent.

 

[RH8448]

whitepatch MD is correct. krukshanks you are right as well however "indep assortment" is a Medelian genetics concept. Independent Assortment is for each gene the inheritance of one allele doesn't effect the inheritance of another allele.

Really, the definition doesn't get into actual chromosomes (linkage etc.) because that was beyond Mendel's time. So knowing the limitations of the definition of independent assortment is important. Its more of a concept or theory and is not meant to be applied to chromosome mapping. Mendel also didn't know about recombination. So I would separate the concepts of "indep assortment" , linkage of genes and recombination.

 

[amy_k]

The result of gene crossing over during synapsis is recombination, not independent assortment. Recombination occurs much later, in the prophase-1 stage, whereas independent assortment as Mendel defined it occurs in anaphase-1. So even though the result of the crossing over is the same as independent assortment, it would never be classified as such, it would be classified as recombination.

In terms of gene linkage, we can have various degrees of linkage. Complete linkage means the gene pair is always inherited together, and when only inherited together a percentage of the time this is incomplete linkage. Gene pairs are classified as linked if fewer than half the gametes from a double heterozygote cross are recombinant.