How do parental chromosomes know how to reform?

[Genecks]

Let's say gametes are being made.

 

How exactly does the big bundle of spaghetti know where to break apart so that complementary homologous chromosomes can be formed and meiosis begun?

 

I'm guessing something unravels the chromatin (HDACs, right?), but what splits it apart in exact positions so that the varying amount of chromosomes can be made to pair up?

[Cap'n Refsmmat]

We're diploid organisms. We have two copies of each chromosome, one from each parent. Each parent thus just donates one copy. It's not that they slice and dice their chromosomes and then the results are reassembled to form a complete human genome.

 

(Admittedly, however, I had the same question several years ago, and it took me a while to realize...)

[Genecks]

Not what I'm necessarily trying to get at.

 

What I'm trying to understand is what biochemical actions (perhaps a simplification) cause the DNA to unravel and package into chromosomes. Furthermore, what makes sure that certain parts of genetic information get into those exact chromosomes?

 

I'm not asking about what causes cell division. I think that's the cyclin-cdk complex or something... Maybe that only applies to mitosis. Either way, I'm on about what chemical processes decided to cut-up the DNA and package it to their respective and designated chromosomes.

 

For instance, what makes sure that particular sections of DNA get into an autosomal chromosome versus a sex chromosome in a human?

 

That question is off from my original question but related. Perhaps I am not asking well enough.

Edited December 24, 2009 by Genecks

[Cap'n Refsmmat]

I'm not sure what you mean by "get into." They're already part of those chromosomes in the parent.

[Genecks]

Let's say that two parents mate:

 

Parent 1: A/A

Parent 2: a/a

 

Independent segregation occurs.

 

The child is A/a.

 

Child inherits a rare and unique heterozygous disorder, which codes for laser eyes and he has to wear red sunglasses for the rest of his life.

 

Now, this child's germ cells undergo meiosis.

The nuclear envelope shatters, and the DNA forms into chromosomes.

The kid will have 23 chromosomes, but the DNA is going to get packages into chromosomes. Scientists have been researching the kids chromosomes and notice that the gene for it is located on chromosome 15.

 

Now, the DNA has to get sliced and diced and put into various chromosomes, right? Am I wrong here?

 

Various chromosomes contain different DNA data from the individual's genome. All of which compose the entire genome?

 

http://en.wikipedia.org/wiki/Human_genome#Information_content

 

So, how do the individuals alleles (one inherited from each parent) in the chromosome (one on each chromatid, since they are independent) know how to form and distance themselves in the composition of the chromosome?

[Cap'n Refsmmat]

The DNA doesn't "form into chromosomes." They're stored in chromosomal form -- as lengths of double helix.

 

In other words, they don't form into chromosomes -- they stay as chromosomes the entire time. They never need to figure out how to remake themselves into chromosomes.

[Genecks]

Are you saying that chromatin does not use condensin I and II factors to form chromosomes?

[Cap'n Refsmmat]

This diagram may help:

http://en.wikipedia.org/wiki/File:Major_events_in_mitosis.svg

 

Chromatin is just the stuff that DNA is composed of.

[Genecks]

I have decided that I will disagree with you.

 

Yes, that's a diagram of mitosis.

Yes, there are many diagrams of meiosis.

I think my question is a little beyond high school biology, though.

 

DNA is composed of nucleotides and a sugar-phosphate backbone.

Chromatin holds histones and DNA.

I'm going to define chromosomes as partitions of chromatin.

 

And from what I've been reading in the past few hours, it would appear that condensin I and II tend to be aligned amongst various parts of the chromatin, and during cell division, they will package the chromatin into chromsomes (chromosome condensation). This is for when the nuclear envelope breaks apart and when chromosomes are turning back into chromatin. Also, I'm getting the impression that my answer can simply not be provided, because current research is attempting to answer my question.

 

In other words, it would appear that the cyclin-CDK complex causes the cell to divide and nuclear envelope to shatter, but the condensin factor causes the chromatin to be partitioned into various chromosomes, which then undergo metaphase, anaphase, and so on.

 

http://en.wikipedia.org/wiki/Condensin

Edited December 24, 2009 by Genecks

[Psycho]

The chromosomes are always held as chromosomes they are just condensed from there free form to the compact form, chromatin. When the chromatin is broken down the chromosomes are set free to allow them to divide and allow recombination to occur, at no point does the chromatid ever come apart completely and as only homologous DNA can recombine and the whole method of mitosis is control by microtubules attached to the centromere it is all kept quite ordered.

 

The only partitioning that happens is moving the chromosomes that have been freed from the histones.