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MCAT Question A Day - 5/14/13 - Answer!

Which statement is correct about homologous pairs of chromosomes?

A.  One homologous chromosome is inherited from each parent.
B.  Homologous chromosomes have genes for the same traits in the same regions (loci).
C.  Homologous chromosomes may be genetically identical for some traits but not others.
D.  All of the above

The correct answer is (D). Individuals receive one whole set of 23 chromosomes from each parent. Thus, we have two #1 chromosomes, two #2 chromosomes, two #3 chromosomes, etc. (one of each homologous pair from each parent). With the exception of the 23rd pair (sex chromosomes X and Y), each pair has genes for specific traits encoded at the same loci. For traits A, B, and C, the maternal chromosome may have alleles A, b, and C. For those traits, the paternal chromosome may have alleles A, B, and c. Thus, the homologous pair of chromosomes has identical genes at locus A, but they are genetically different at loci B and C.