Chromatids/Chromosomes?

[MichaelXY]

I did a search on chromsomes, and although the list was quite extensive I did not find my exact question. So pardon me if I am being redundant.

I find myself getting confused when talking about chromosomes. Here is where I get confused:

| <---- A single strand is shown as a chromosome.

X <---The strands bind at the centromere and are called sister chromatids.

So is a chromatid made up of 2 chromosomes?

Is one strand | considered 1 set of chromosomes?

Is 2 strands X considered 2 sets of chromosomes?

In mitosis we would start with 2 sets in X then 4 sets out XX ?

As you can see I am quite confused. I have a test on Monday so any help would be great.

Thanks

[Darby]

It's all definitions, kind of a consensus of what we'll all call things. Sometimes they make more sense than others. We could refer to chromatids as sister chromosomes, but there would be times when that would be confusing too. As it stands, they are called double-stranded chromosomes until they separate into single-stranded chromosomes (and that can confuse someone who's thinking about the DNA already being double-stranded...).

[MichaelXY]

Thanks for the reply. I think I got that, but I am still befuzzled. I think I have broken brain.

Ok, In meiosis we have all these cells running around our bodies. These cells have 2 sets of chromosomes, 1 from mom the other from dad. In order to procreate, our body needs to make sperm or egg cells.

So we have these diploid cells with 46 somes. This will not work if we just duplicate since we will have 96, so we split the some into 1 strand of 23.

Do I have it thus far?

To make a sperm or egg cell we split the 2 sets into 1 sets called haploids.

These haploids are now sperm or egg cells.

Is that the end of the meiosis phase.

During reproduction the sperm haploid joins the egg haploid and becomes a diploid. From the diploid cell, a zygote, it multiplies through mitosis.

Do I have it right?

Thanks

[Poison]

I think I know the reason of your confusion.
As you said:
l ---> 1 chromosome. But you can not see this structure if the cell is not in the telophase.
X---> this is still 1 chromosome. The difference is that this structure is only seen in metaphase. This is a metaphase chromosome, made up of 2 sister chromatids. When they split up we call each of them "chromosome".
l and X are 1 chromosome. X has dublicated itself thats all.
Homologous chromosomes are different from X structure. X does not symbolize homologs. XX or ll can symbolize it.
Each chromatid of X is identical. Homolog chromosomes are not identical. They just carry the same loci that controls the same thing. (allels can be different)
Is it clear now?


And yes you are right about the last part.
2n---->n (meiosis)
n+n=2n (fertilization)
2n goes on dividing (mitosis)

[MichaelXY]

Thanks for responding. It is around 2 AM here, my test is in the morning, and I think I got it. I have 1 more chapter to go over. I am tired.

Thanks

[MichaelXY]

Not that anyone cares, but I got a 83% on my test. Darn thing is, there were maybe 2 questions on what I was worried about. Go figure. I spent so much time on the part I did not have a strong grasp on, I neglected the stuff that just required memorization. Geez I hate test...

[david23]

what did u get wrong

[Poison]

%83 is fine.