Chromosomes and stuffs

[bucket]

Yeah I'm finding it hard to get my head around some of these things for some reason.

Firstly, is it true that chromosomes normally exist as a single chromatid, and only develop the other chromatid to form an X shape during DNA replication during the S-phase of interphase??
Second, in crossing over, if the swapping of genes occurs between a homologous pair of chromosomes, at the same gene loci, how is that a cause for variation? If they are homologous chromosomes doesn't this mean that they have the SAME genes at that same gene loci, and therefore would just be exchanging the SAME gene to one another? Lol I'm so confused!!

[username]

Are you asking the first question because of the TSFX lecture thing and how she said something about a 'non dividing cell's chromatid being called a general chromosome or something? Cuz she lost me there.

[bucket]

haha you were there too? the first presenter wasn't really good :S. Anyway yeah, she brought it to our attention but didn't explain why and stuff.

[username]

I KNOW! I think I'm just going to ignore that detail though, because it's started to confuse me with everything else.

I didn't really like the second presenter either, the whole "Okay so now we're going to skip from page.. 10 to... 61" didn't cut it for me.

Were you there today for the Chemistry one? I found that hella good. But the seats in the med building are so terrible. I felt like someone blew off my lower torso.

[bturville]

Firstly, is it true that chromosomes normally exist as a single chromatid, and only develop the other chromatid to form an X shape during DNA replication during the S-phase of interphase?

yep. you should be able to see this in most diagrams of mitosis.

Second, in crossing over, if the swapping of genes occurs between a homologous pair of chromosomes, at the same gene loci, how is that a cause for variation? If they are homologous chromosomes doesn't this mean that they have the SAME genes at that same gene loci, and therefore would just be exchanging the SAME gene to one another? Lol I'm so confused!!

the gene loci are the same yes, but the ALLELES at those loci are often different on the homologous chromosomes, leading to variation.

[bucket]

oh, i see!
thanks a heap man <3. my textbook doesn't have a diagram of the non-dividing stages :S.

I KNOW! I think I'm just going to ignore that detail though, because it's started to confuse me with everything else.

I didn't really like the second presenter either, the whole "Okay so now we're going to skip from page.. 10 to... 61" didn't cut it for me.

Were you there today for the Chemistry one? I found that hella good. But the seats in the med building are so terrible. I felt like someone blew off my lower torso.

Nah, I had a methods lecture today, decided to give chem a skip...too expensive to do 3 >.<
I have the methods lecture in the med building tomorrow :S

[username]

oh, i see!
thanks a heap man <3. my textbook doesn't have a diagram of the non-dividing stages :S.

I KNOW! I think I'm just going to ignore that detail though, because it's started to confuse me with everything else.

I didn't really like the second presenter either, the whole "Okay so now we're going to skip from page.. 10 to... 61" didn't cut it for me.

Were you there today for the Chemistry one? I found that hella good. But the seats in the med building are so terrible. I felt like someone blew off my lower torso.

Nah, I had a methods lecture today, decided to give chem a skip...too expensive to do 3 >.<
I have the methods lecture in the med building tomorrow :S

There was a boy sitting in front of me and his sign up sheet had him enrolled in every lecture for all his subjects.

I was going to go to the methods one but I'm too shit scared that I'll realize I know nothing and be unmotivated/depressed.

[bucket]

...damn those lucky rich people

[Toothpaste]

Just thought I'd post nice pictures lol:
MITOSIS (interphase = not part of mitosis)




(will upload meiosis by request...)

In regards to TSFX, the first lecturer went sooooo slow.

[bturville]

and more, courtesy of friendly wikipedia:

[bucket]

wow those are great!

[bucket]

MMMMM gene linkage?
what exactly is this?!!!!
are genes said to be 'linked' when they are close together on a chromosome and therefore are inherited together during crossing over, or did I completely misunderstand it?

[Toothpaste]

MMMMM gene linkage?
what exactly is this?!!!!
are genes said to be 'linked' when they are close together on a chromosome and therefore are inherited together during crossing over, or did I completely misunderstand it?

• Yep, the loci of the linked genes would be closer together, on the same chromosome. In meiosis the laws of independent assortment cannot be applied to linked genes ... because they do not assort independently of each other.
• During crossing over there's a higher chance of them both to be inherited together.
  
  Here's why in a DIY, analogy form:
  
  (No, don't be emo and slit wrists.)
  
  Let's say your arms are chromosomes.
  In diagram 1: Alleles of closely linked genes
  In diagram 2: Alleles of more separated genes
  
  
  Your other arm, crossing over, would have more chance taking both A and B alleles rather than A and C as the former combination is closer together.
  higher chance of them both to be inherited together
  
  Q.E.D. (haha)

My little analogy is not what "exactly" happens when chromosomes cross over .. (ie omitted switching and all that) ..

Oh and a more professional picture, lol:



almost 4am zzzzz

[bucket]

hahaha good explanation!
thanks

[bilgia]

Just thought I'd post nice pictures lol:
MITOSIS (interphase = not part of mitosis)
(Image removed from quote.)
(Image removed from quote.)



(will upload meiosis by request...)

In regards to TSFX, the first lecturer went sooooo slow.

straight outta my uni bio textbook lol.