Question

which best describes a centromere?
sister chromosomes that are held together by a chromatid
paired chromosomes that have genes arranged in the same order
the part of a chromosome that joins the sister chromatids
the material that makes up a chromosome

Explanation:

To determine the correct description of a centromere, we analyze each option:

• Option 1: Sister chromosomes held by a chromatid is incorrect; sister chromatids are held by the centromere, not sister chromosomes by a chromatid.
• Option 2: Paired chromosomes with genes in the same order refers to homologous chromosomes, not centromere.
• Option 3: The part of a chromosome that joins sister chromatids is the definition of a centromere.
• Option 4: The material making up a chromosome is chromatin (DNA + proteins), not centromere.

Answer:

the part of a chromosome that joins the sister chromatids (the third option in the list, corresponding to the option with text "the part of a chromosome that joins the sister chromatids")