Question about Mitosis

[gotGino]

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So here is my dilemma.

I'm looking at these two karyotypes.

Karyotype 1: http://www.biotechnologyonline.gov.a.../karyotype.jpg
Karyotype 2:http://www.contexo.info/DNA_Basics/i...karyotype1.gif

Now karyotype 1, each chromosome is depicted as 2 bars. In karytope 2, each chromosome is depicted as 2 Xs. Which one is it? Is the one bar a more condensed version of one X.

It's confusing me because many pictures of mitosis show the replication of a bar, then when duplicated its the sister chromosomes depicted as an X, and then they split again as a bar, like the image here:http://upload.wikimedia.org/wikipedi...in_mitosis.svg.

The way this looks to me, a somatic cell appears haploid because the chromosome looks singular rather than a pair after it's divided. Now if that one bar was actually an X, then it would totally make sense to me.

Any help is greatly appreciated. Thanks.

 

[Cinclus]

Now karyotype 1, each chromosome is depicted as 2 bars. In karytope 2, each chromosome is depicted as 2 Xs. Which one is it? Is the one bar a more condensed version of one X.

No, it is not a more condensed version. The "X" appearance occurs after the synthesis of sister chromatids. The "X's" split after metaphase, with one side of each "X" going to each of the daughter cells (the chromatids are referred to as chromosomes after this separation).

It's confusing me because many pictures of mitosis show the replication of a bar, then when duplicated its the sister chromosomes depicted as an X, and then they split again as a bar, like the image here:http://upload.wikimedia.org/wikipedi...in_mitosis.svg.

The way this looks to me, a somatic cell appears haploid because the chromosome looks singular rather than a pair after it's divided. Now if that one bar was actually an X, then it would totally make sense to me.

In mitosis, the chromosomes do not join up with their homologues, as they do in meiosis. The "X" is the joined sister chromatids.

 

[mcloaf]

Image one is the entire complement of unreplicated chromosomes. So for example the two "bars" under the different numbers are the maternal and paternal copies of the same chromosome.

In image two the DNA has been replicated. What you're seeing here at two copies of each of the parental copies for all the chromosomes joined at the centromeres. So the two parts of each X are actually identical, whereas the other X labeled with the same number is two identical copies of the other homologous c'some from the other parent.

The somatic cell is not haploid--each of those two bars under the numbers are the "same" chromosome, but each copy is from one parent. In mitosis all of the X's split in half so each cell has an entire set of chromosomes, one set from each parent.

 

[gotGino]

Thanks for the help guys! It makes sense now.