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I recently read a comparison between behaviour of chromosomes and genes - which had two statements understated -

  1. Independent pairs segregate independently of each other

  2. One pair segregates independently of another pair

I further found that the first one indicates segregation pattern of gene and the second accounts for chromosome.

But that bothers me, I am unable to compare chromosome and gene on this basis. I feel the two statements really confusing and it appears to me that both the statements apply both to chromosomes and genes.

Though, law of segregation for genes includes one pair of genes that segregate independently of each other but independent pairs too segregate independently of other pairs. As genes are present on chromosomes, what then defines their segregation differently.

Also, what does segregation of chromosomes imply? Does it include separation of sister chromatids in anaphase of meiosis as well as mitosis or separation of bivalents also during meiosis?

Is the question biased on independent assortment more than segregation pattern, please do correct me.

Those doubts appear absurd to me, but I hope that someone would help me, please.

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The difference is:

  • Different chromosomes always segregate independently

  • Different genes may or may not segregate independently

There are different mechanisms at work. The chromosomal segregation mechanism always separate chromosomes randomly (independently), as whole chromosomes are moved as a unit.

A different mechanism causes segregation of genes that reside on the same chromosome. It sends only large pieces of the chromosome to different daughter cells. Each piece contains many genes, so within a piece, the genes don't separate at all, so do do not segregate independently.

When two genes are on different chromosomes, they segregate independently because their chromosomes segregate independently. When two genes are on the same chromosome, they do not segregate independently since they may end up on the same segregating piece of their chromosome.

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  • $\begingroup$ what about chromatid separation? Don't they segregate independently from each other. $\endgroup$ – Vidhi Gupta Oct 22 '17 at 21:20
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Direct quote, please!

Please, when you are referring to something you've read, always add a link and attempt to offer direct quote. From your question it is a little hard to understand what is the original claim about. I suspect the following will help you though.

First, definitions

First, you might want to make sure, you know the definitions of

Segregation and recombination

There are two concepts you shall examine. Segregation and Recombination

Segregation

Segregation is the process by which hommologous chromosomes are independently separated into different cells during meiosis. The concept of segregation was first discovered by Mendel and expressed in his law of segregation

The Law of Segregation states that every individual organism contains two alleles for each trait, and that these alleles segregate (separate) during meiosis such that each gamete contains only one of the alleles.

Note that this law is partially (or mainly) wrong as it assumes that each phenotypic trait is affected only by a single locus with two alleles which is actually very rare.

Recombination

I am here describing recombination by its effects and by relating it to segregation. Recombination is the process that causes genes phyiscally linked on the same chromosome to not segregate entirely together. Recombination is caused by chromosomal cross-over, which are "recombination" between the "content" of the two homologous chromosomes. When chromosome segregate, it is actually the recombined chromosomes that segregate (in terms of the molecular machinery both process of segregation and recombination happen very much at the same time actually).

The concept of recombination has been discovered by Morgan with his fruit flies experiments. The Morgan is actually used today as a unit of recombination distance between two loci.

Source of information

You can have a look at any intro course to genetic such as these courses by Khan Academy for example.

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  • $\begingroup$ Sorry for not providing link. I would try adding link next times. $\endgroup$ – Vidhi Gupta Oct 22 '17 at 16:25
  • $\begingroup$ @VidhiGupta No worries. We all go through the phase of learning to ask very good questions. $\endgroup$ – Remi.b Oct 22 '17 at 19:07
  • $\begingroup$ Definitely. This one is just the second question I have asked on this site and I am actually happy about it. Hope I would get an answer to my queries or maybe some more queries...😃😃 $\endgroup$ – Vidhi Gupta Oct 22 '17 at 21:18

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