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after dna replication during s phase of interphase, each chromosome has a copy and the cell is now 4n. we call these identical pairs and they are held together by a

a. homologous pairs; centrosome.
b. sister chromatids; histone.
c. homologous pairs; histone.
d. sister chromatids; centromere.

D. sister chromatids; centromere

Explanation:

Chromosomes are made up of two filaments joined by the centromere. Each of these filaments is called a chromatid. The two chromatids found on a duplicated chromosome (duplication occurs during the interphase in cell division) are called sister chromatids. In the process of cell division, they separate, each going to a daughter cell.

In other words, we can say that after DNA replication during the S phase of the interphase, each chromosome has a copy and the cell is now 4n. We call these identical pairs of sister chromatids and they are held together by a centromere.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.