Confused on cell division..?

[Ari1584]

This might sound kind of stupid but i have been a little confused on some important topics in cell division. I have written out my understanding of cell division/chromosomes, and if anything is wrong, can someone please correct me/verify that my thinking is correct?

1. A chromosome consists of 2 sister chromatids that are completely identicle to each other (so each chromatid has 46 chromosomes?). Each chromosome has a homologous chromosome that is its partner and has a different trait for the same gene? Like one chromosome is for blue eyes and the homologous pair is for brown eyes. Now is one pair from a mom and the other homologous pair is from the dad?😕

2. When we say humans have 23 pairs of chromosomes, does that mean 23 chromosomes and 23 homologous chromosomes, so 46 all together and 23 pairs? (i feel like im making this harder than it really is)

3. During mitosis, chromosomes line up the middle in metaphase and split up so each sister chromatid goes to the opposite side of the cell. The part im confused about is, when cytokinesis occurs, each cell gets a chromatid, but then how does it become a chromosome again if it only got one chromatid?

Thanks!🙂

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[ksmi117]

This might sound kind of stupid but i have been a little confused on some important topics in cell division. I have written out my understanding of cell division/chromosomes, and if anything is wrong, can someone please correct me/verify that my thinking is correct?

1. A chromosome consists of 2 sister chromatids that are completely identicle to each other (so each chromatid has 46 chromosomes?). Each chromosome has a homologous chromosome that is its partner and has a different trait for the same gene? Like one chromosome is for blue eyes and the homologous pair is for brown eyes. Now is one pair from a mom and the other homologous pair is from the dad?😕

2. When we say humans have 23 pairs of chromosomes, does that mean 23 chromosomes and 23 homologous chromosomes, so 46 all together and 23 pairs? (i feel like im making this harder than it really is)

3. During mitosis, chromosomes line up the middle in metaphase and split up so each sister chromatid goes to the opposite side of the cell. The part im confused about is, when cytokinesis occurs, each cell gets a chromatid, but then how does it become a chromosome again if it only got one chromatid?

Thanks!🙂

1. Yes-ish. The chromatids only exist during cell division. A normal chromosome is just that, one normal chromosome. If the cell is replicating, the sister chromatids are pulled apart and are found in the two new cells each as the one normal chromosome. During the early stages of mitosis, a human cell has 23 pairs of homologous chromosomes (46 different chromosomes) and each chromosome has 2 chromatids (so technically 92 chromatids). Your logic about the homologous chromsomes is correct though.

2. Yes, 46 total chromosomes.

3. Once they are separated into the cells, the chromatid is the chromosome. A chromosome doesn't need to have two chromatids to be a chromosome. The chromatids only exist after the strand is replicated in preparation for cell division.

 

[Revilla]

Here's the way I understand it (and someone please correct me if I'm wrong).

(1) Every human being has a total of 46 chromosomes (23 pairs). You get 23 chromosomes from your father and 23 from your mother.

(2) Chromatids are just replicated chromosomes. Each chromosome is made up of two chromatids before cell division (so sister chromatids together make up a chromosome). In a human, during the S phase, each cell has 92 chromatids, but since they're just replications of the same chromosome, it's still 46 chromosomes.

(3) Sister chromatids carry identical alleles (they're replicated chromosomes, don't forget). Homologous chromosomes carry the same genes, but not the same alleles. So, for example, you have two genes for eye color that you inherited from your parents -- one is blue eyes for your dad and one is brown eyes for your mom. These chromosomes together are homologous chromosomes. That's what makes up the pair -- one from your mom and one from your dad.

(4) After cytokinesis, the cell separates, but each cell has 46 chromosomes. Each chromosome doesn't have a sister chromatid at this point because immediately after cytokinesis, it hasn't replicated yet. Once it begins the replication process again, the chromosomes will have their chromatids and the cycle begins again.

ETA: ksmi replied while I was typing so my post is redundant, but I'll leave it up anyway 🙂

 

[ping3pong]

This might sound kind of stupid but i have been a little confused on some important topics in cell division. I have written out my understanding of cell division/chromosomes, and if anything is wrong, can someone please correct me/verify that my thinking is correct?

1. A chromosome consists of 2 sister chromatids that are completely identicle to each other (so each chromatid has 46 chromosomes?). Each chromosome has a homologous chromosome that is its partner and has a different trait for the same gene? Like one chromosome is for blue eyes and the homologous pair is for brown eyes. Now is one pair from a mom and the other homologous pair is from the dad?😕

2. When we say humans have 23 pairs of chromosomes, does that mean 23 chromosomes and 23 homologous chromosomes, so 46 all together and 23 pairs? (i feel like im making this harder than it really is)

3. During mitosis, chromosomes line up the middle in metaphase and split up so each sister chromatid goes to the opposite side of the cell. The part im confused about is, when cytokinesis occurs, each cell gets a chromatid, but then how does it become a chromosome again if it only got one chromatid?

Thanks!🙂

After a diploid cell replicates (in the S1) it is 4n. It has twice the number of DNA it needs. Each chromatid has half 2n or both of the traits. For haploid cells each chromatid only has 1n or one allele of a certain trait. This happens in the second stage of meiosis after the cell has not replicated its DNA again.