Really quick bio question

BiomajorPreDent

Senior Member
10+ Year Member
A cell has 12 chromosomes at the end of mitosis. How many chromosomes would it have in the G2 phase of its next cell cycle?

-6
-9
-12
-24
-It depends on whether it is undergoing mitosis or meiosis

I picked 24, because G2 occurs after S, and it would have already doubled its DNA for division..

But the book says its 12

Can someone please shed some light on this?

Is it because each chromosome consists of two sister chromatids? and thus since it has 24 sister chromatids, it still has only 12 chromosomes?

I am usually good at this stuff but now im confused...

Aljazera

Removed
when you want to count CHROMOSOMES, count the number of CENTROMERES to give you the number of CHROMOSOMES.

Even though, they have 2 sister chromatids, they are attached to a SINGLE CENTROMERE, which means its considered to be ONE chromosome.

OP
B

BiomajorPreDent

Senior Member
10+ Year Member
Okay, so just to sum it up:

Each chromosome has 1 centromere and 2 chromatids with 2 kinetochores

right?

nze82

A cell has 12 chromosomes at the end of mitosis. How many chromosomes would it have in the G2 phase of its next cell cycle?

-6
-9
-12
-24
-It depends on whether it is undergoing mitosis or meiosis

I picked 24, because G2 occurs after S, and it would have already doubled its DNA for division..

But the book says its 12
Mitosis produces sister cells with exactly the same # of chromosomes. In other words, unlike Meiosis, Mitosis doesn't reduce the number of chromosomes by 1/2. So you start with 12 and you end up with 12.
It's true that G2 is after the S phase, but the S phase simply adds a sister chromatid to each chromosome. So, the # of chromosomes remains the same, but the amount of DNA material doubles.

Can someone please shed some light on this?

Is it because each chromosome consists of two sister chromatids? and thus since it has 24 sister chromatids, it still has only 12 chromosomes?

I am usually good at this stuff but now im confused...
Hope this helps!

Aljazera

Removed
Okay, so just to sum it up:

Each chromosome has 1 centromere and 2 chromatids with 2 kinetochores

right?
No. What do kinetochores have to do with this?

2 SISTER chromatids are attached to a single Centromere, for example, which is considered as ONE chromosome.

So in G2, since they DNA does duplicate, it still is one chromosome.

Think of it this way, If I get fat, I'm still one person, not two. Because I'm attached to the same body.

OP
B

BiomajorPreDent

Senior Member
10+ Year Member
Right I got it, I asked about kinetochores because I was curious as to how many of them that there are

Also there were two other questions in my bio text but I think one of them is a typo

A cell with diploid number 6 could produce gametes with how many different combinations of maternal and paternal chromosomes?

6
8
12
64
128

the book gives 8 as the answer, which corresponds to 2^3, which is the haploid number

In a sexually reproducing species with a diploid number of 8, how many different combinations of paternal and maternal chromosomes would be possible in the offspring?

8
16
64
256
512

the book gives 256 as the answer, which corresponds to 2^8 and 8 is the diploid number

Maybe my brain is just tired, but I thought these questions were asking the same thing, why did one use n and the other use 2n to solve these?

Heres the sentance the book gave before the question section:

"The number of possible combinations of maternal and paternal chromosomes is 2^n, where n is the haploid number"

dennisDDS

10+ Year Member
Right I got it, I asked about kinetochores because I was curious as to how many of them that there are

Also there were two other questions in my bio text but I think one of them is a typo

A cell with diploid number 6 could produce gametes with how many different combinations of maternal and paternal chromosomes?

6
8
12
64
128

the book gives 8 as the answer, which corresponds to 2^3, which is the haploid number

In a sexually reproducing species with a diploid number of 8, how many different combinations of paternal and maternal chromosomes would be possible in the offspring?

8
16
64
256
512

the book gives 256 as the answer, which corresponds to 2^8 and 8 is the diploid number

Maybe my brain is just tired, but I thought these questions were asking the same thing, why did one use n and the other use 2n to solve these?

Heres the sentance the book gave before the question section:

"The number of possible combinations of maternal and paternal chromosomes is 2^n, where n is the haploid number"
For sexual species you have the sperm and the egg

2^4 for sperm

2^4 for egg

sperm + egg = 2^4 x 2^4 = 2^8 or 256