Genetics Terms

[MedPR]

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I'm having a really hard time grasping and differentiating between all the general genetics terms. This might be too much for one thread and if it is, I'll make more.

1. I don't know the difference between a chromatid and a chromosome and chromatin.
2. Does every somatic cell have 22 pairs of all the autosomal chromosomes?
3. How can you identify which parent(s) nondisjunction occured in?
4. After S phase leading up to Meiosis 1, are there 46 pairs, or a total of 92 chromosomes in each cell? If not, how many are there?

 

[chiddler]

I'm having a really hard time grasping and differentiating between all the general genetics terms. This might be too much for one thread and if it is, I'll make more.

1. I don't know the difference between a chromatid and a chromosome and chromatin.
2. Does every somatic cell have 22 pairs of all the autosomal chromosomes?
3. How can you identify which parent(s) nondisjunction occured in?
4. After S phase leading up to Meiosis 1, are there 46 pairs, or a total of 92 chromosomes in each cell? If not, how many are there?

1. A chromosome consists of two sister chromatids. This means the X shaped chromosome can be separated into two linear strands called a sister chromatid. Chromatin is the material that the nucleus contains when DNA is condensed. This means histones + supercoiled DNA.

2. Every somatic cell has 22 pairs of the the autosomal chromosomes. This, of course, does not necessarily apply to all organisms. Bees, if I remember correctly, are haploid if male, diploid if female. Something like that...

3. Need example! :x

4. S phase is synthesis phase, right? That means the cell is replicating its DNA. Therefore, after completion, it has doubled its chromosome number. Your numbers are correct.

Edit: Here you go 😀 Ask if you need, but I think this illustration explains it well enough.

 

[MedPR]

1. A chromosome consists of two sister chromatids. This means the X shaped chromosome can be separated into two linear strands called a sister chromatid. Chromatin is the material that the nucleus contains when DNA is condensed. This means histones + supercoiled DNA.

2. Every somatic cell has 22 pairs of the the autosomal chromosomes. This, of course, does not necessarily apply to all organisms. Bees, if I remember correctly, are haploid if male, diploid if female. Something like that...

3. Need example! :x

4. S phase is synthesis phase, right? That means the cell is replicating its DNA. Therefore, after completion, it has doubled its chromosome number. Your numbers are correct.

Edit: Here you go 😀 Ask if you need, but I think this illustration explains it well enough.

That's exactly how I understand nondisjunction, but there were TBR questions that gave some image (like this one: http://jmg.bmj.com/content/37/7/525/F1.large.jpg) and asked if nondisjunction occured in the mother or the father. I'll find the problems when I get home.

 

[JD7]

On #4 you have 46 Chromosomes and 92 Chromatids.

1 chromatid = 1 chromosome
a pair of chromatids = 1 chromosome

It's kinda confusing.

This could help you - http://www.khanacademy.org/video/chromosomes--chromatids--chromatin--etc?playlist=Biology

 

[Pisiform]

 

[MedPR]

Thank you everyone. Also, I figured out the nondisjunction question. I was misreading the chart...

The other thing I was wondering about is what happens after fertilization..

You have a haploid sperm that fertilizes a haploid egg right? So do those undergo meiosis or what?

 

[milski]

You have a haploid sperm that fertilizes a haploid egg right? So do those undergo meiosis or what?

They fuse together to make a diploid zygote. It starts quickly dividing by mitosis. Meiosis will not come in the picture until ovaries start to form or testicles start functioning.

 

[MedPR]

They fuse together to make a diploid zygote. It starts quickly dividing by mitosis. Meiosis will not come in the picture until ovaries start to form or testicles start functioning.

So the egg pre-fertilization is suspended in metaphase 2... When does it complete meiosis?

 

[milski]

So the egg pre-fertilization is suspended in metaphase 2... When does it complete meiosis?

The entry of the sperm triggers the completion of meiosis for the egg.

 

[MT Headed]

It is almost magic, but the sperm's chromosomes end up in one side of the egg, and the polar body is ejected (and thrown away) from the other side of the egg along with half od the egg's chromatids. It would be quite a crisis if some or all of the male chromosomes went into the disposable polar body by mistake!

 

[IH8ColdWeath3r]

On #4 you have 46 Chromosomes and 92 Chromatids.

1 chromatid = 1 chromosome
a pair of chromatids = 1 chromosome

It's kinda confusing.

This could help you - http://www.khanacademy.org/video/chromosomes--chromatids--chromatin--etc?playlist=Biology

yeah, took me a while to get this and it is confusing but after S phase, when the DNA has replicated, you still have 4 chromosomes and the cell is STILL DIPLOID (because you are not introducing any new genetic material into the cell, your only replicated). the X structure is still ONE chromosome, it is just a replicated chromosome after S phase.