Chromosome/Chromatid Question

[The Phlebotomist]

Is this Correct?

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[NextStepTutor_2]

Is this Correct?

Prior to DNA replication (S phase), our cells contain 46 chromosomes. During S phase, all 46 chromosomes are copied, and because they are identical copies, it is accurate to say that there are now 92 (46 + 46) chromosomes in the nucleus.

But, "chromatid" is a term used to describe them until the completion of cell division. A chromatid is just what you would call a chromosome during mitosis. In addition, the chromatids are stuck together after S phase, so we could also say that there are 46 pairs of chromatids (or chromosomes) at the end of S phase, and be no less accurate. Once the (autosomal) cell goes through mitosis, these 46 pairs will separate into 2 identical daughter cells, each with 46 chromosomes.

 

[The Phlebotomist]

Prior to DNA replication (S phase), our cells contain 46 chromosomes. During S phase, all 46 chromosomes are copied, and because they are identical copies, it is accurate to say that there are now 92 (46 + 46) chromosomes in the nucleus.

But, "chromatid" is a term used to describe them until the completion of cell division. A chromatid is just what you would call a chromosome during mitosis. In addition, the chromatids are stuck together after S phase, so we could also say that there are 46 pairs of chromatids (or chromosomes) at the end of S phase, and be no less accurate. Once the (autosomal) cell goes through mitosis, these 46 pairs will separate into 2 identical daughter cells, each with 46 chromosomes.

Is the question posted referring to "Each" cell or chromosome in your opinion?

 

[5words]

Prior to DNA replication (S phase), our cells contain 46 chromosomes. During S phase, all 46 chromosomes are copied, and because they are identical copies, it is accurate to say that there are now 92 (46 + 46) chromosomes in the nucleus.

But, "chromatid" is a term used to describe them until the completion of cell division. A chromatid is just what you would call a chromosome during mitosis. In addition, the chromatids are stuck together after S phase, so we could also say that there are 46 pairs of chromatids (or chromosomes) at the end of S phase, and be no less accurate. Once the (autosomal) cell goes through mitosis, these 46 pairs will separate into 2 identical daughter cells, each with 46 chromosomes.

That's actually not accurate.

Throughout cell division the Cell has 46 chromosomes or 23 pairs of chromosomes. Here what you need to keep track of are Centromeres. 1 centromere = 1 chromosome. Thus chromosomes are very different from chromatids, chromatids are copies of chromosomes. Like, i have alluded below, think of a chromosome as a gene (since genes are carried on chromosome and a chromatid as an allele for the sake of discussion).

So in the G1 phase , the membrane bounds organelle replicates allowing the cell to go through the mitosis checkpoint in the G1 phase, thus entering the S phase.hence, Prior to the S phase, the cell has 23 pair of chromosomes or 46 chromatids because each chromosome has 2 strand known as chromatid (another way to see this is to conceptualized the chromosome as a gene and the chromatid as allele); so once into the S phase, those chromosome duplicate to give rise to 23 pair of chromosomes, and each chromosome two has 4 chromatid which are joined together by a single centromere (only in mitosis, in meiosis they formed bi-valent). Thus in the G2 phase the cell now has 23 pair of chromosome or 46 chromosomes and 92 chromatids. As you have noticed , the S phase only double the number of Chromatid! Then the cell will enter mitosis, in Prophase the cell has 46 chromosome or 23 pairs of chromosome and 92 chromatids . You have the same organization in metaphase -- in anaphase however, the centrome are split apart thereby leading to the formation of two cell each with 23 pairs of chromosomes (because 1 centromere = 1 chromosome) but 42 chromatids (because the sister chromatids are splited in half during this phase (1/2 go to one cell (46) the other half go to another cell (46)).. At this point the cell is said to be haploid. Why? because although, the cell still has 23 pairs of chromsomes, it no longer have 2 copies of chromosomes (known as chromatids), that is each chromosome only carry one copy at this point. Thus each daughter cells only have one copy now.


Now the process in meoisis is a lot different, but the picture you posted is correct. Let me know if you want me to go over meiosis as well.

Is the question posted referring to "Each" cell or chromosome in your opinion?

No the question is referring to the "Cell" and is correct. but, i don't like how they used the word chromatid.. because you have no chromatids prior to the S phase.