IMAT 2012 Q50 [Chromosomes]

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1

Which one of the following is NOT correct about human chromosomes?

A. They contain regions called genes.
B. They are made of DNA and protein.
C. They are sometimes not found in pairs
D. They can attach to the spindle at the centriole.
E. They are sometimes found in pairs.

2

The answer to this question is D.

Let us then analyze why choices A, B, C, and E are correct:

  • They contain regions called genes: Genes are the basic unit of our inheritance, and they dictate our phenotypes, which is why they are often called our “blueprint”. Genes are basically made up of DNA, and how exactly are chromosomes concerned with DNA? Each chromosome contains DNA, and its unique structure keeps it tightly wrapped, this is to ensure that they will be able to fit inside cells.

  • They are made of DNA and protein: As mentioned above, the characteristic structure of chromosomes allows it to be compact. This compact structure is made possible by proteins called histones, where DNA is tightly wrapped around these proteins like a spool. This combination of protein and DNA also provides stability to the whole structure.

  • They are sometimes found in pairs. & They are sometimes not found in pairs: Usually, chromosomes are arranged in pairs within the nucleus of the cell. We humans have 23 pairs of chromosomes which makes a total of 46 chromosomes. However, it is possible for chromosomes to not be in a pair, which are found in gametes or human reproductive cells, where each gamete carries 1 copy of each chromosome. When 2 gametes from each parent unites, this forms a single cell that contains 2 copies of each chromosome.

Why is “They can attach to the spindle at the centriole.”, wrong?

  • This is a false statement, since spindles attach to centromeres and not centrioles.
  • To prevent being confused over centrioles and centromeres, let’s list a few key differences between the two. A centriole is a cylindrical organelle made of microtubules within the cell, whereas a centromere is a region of the chromosome made of heterochromatin that connects 2 sister chromatids. The main function of a centriole is the synthesis and organization of spindle fibers, while on the other hand, centromeres serve as attachment sites to the spindle fibers.
  • Thus, with this comparison in mind, it would now make sense why choice D is the correct answer, since it does not correctly describe the nature of human chromosomes.