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Question by ricky g: How many chromosomes are present in a cell during interphase (it is about to do mitosis)?How many chromosomes are present in a cell during interphase (it is about to do mitosis)?
There were 28 chromosomes total. How many are there now? 28? How many chromatids are now present? How many homologous pairs are present? I am a bit confused between chromosome and chromatid and what happens to them during interphase.
And YES, I have gone to Wikipedia so if that was your answer then you are no help at all.
Best answer:Answer by science girl
Answers here... explanation to follow:
Before S phase:
2n = 28 total chromosomes
14 homologous pairs (n=14)
This looks like 28 "I"s
Each "I" is a single chromosome
After S phase:
4n = 56 total chromosomes
14 replicated homologous pairs in the form of 56 chromatids, 28 pairs of chromatids
This looks like 28 "X"s, each X is composed of 2 chromatids.
Chromatids are the replicated copy of an original chromsome that are still connected to the original chromsome at the centromere.
Explanation:
Let's assume the organism is diploid, like humans, meaning that a mom and a dad each contribute a set of chromsomes. If this is the case, and the cell has 28 total chromosomes, then that means that 14 came from mom and 14 came from dad. A diploid organism has 2 copies of each chromosome. So, this org has 14 different chromosomes, just 2 of each: for ex- AA, BB, CC, DD, EE, FF, GG, HH, II, JJ, KK, LL, MM, NN. Chromosome A might carry the genes ( the info) for hair color. On the copy of A from mom the info might say blond hair, while the copy from dad might specify that the color of the hair should be brown.
So, this means that 14 homologous pairs are present. A from dad is a homolog of A from mom = 1 homologous pair. B from dad is a homolog of B from mom = 2nd homologous pair, etc. all the way up to 14 homologous pairs = 28 total chromosomes.
During S phase of interphase, all DNA is copied, xerox'ed, replicated. So chromosome A from mom gets duplicated- so now there is an original and a copy. These are called chromatids and they remain attached to one another at the centromere. THe same thing happens to chromosome A from dad. It gets copied- resulting in an original A from dad and a copy of A from dad = 2 chromatids that stay connected at the centromere. The same thing happend to each of the remaining 13 chromosomes from mom and the 13 chromosomes from dad. SO, at the end of S phase (S stands for synthesis of DNA-the copying) of interphase, there are twice as many chromosomes as we started with. If n (the number of different chromsomes in a genome) = 14, the cell before S phase is 2n (it has a homologous pair of each of the 14 chromsomes (A-N), and the cell after S phase is 4n (4Xn=56).
MItosis is the process that gets the 2 daughter cells back to 2n-diploid.
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