Question

When human DNA molecules and chimpanzee DNA molecules are heated to separate the two sides of the molecules from each other and then mixed together at cooler temperatures, strands of human DNA are able to form hydrogen bonds and base-pair with over $98\%$ of the nucleotides in the chimpanzee DNA strands. Which of the following is the most logical conclusion to draw from this information?
A. Humans evolved from chimpanzees.
B. Humans and chimpanzees share a relatively recent common ancestor.
C. Chimpanzees evolved from humans.
D. Convergent evolution has led to similar nucleotide sequences in the two genomes.

Answer 1

Hint: Human and chimp are so closely related that is why their DNA is so similar to each other. Humans, chimps and bonobos have a single ancestor species which lived about six to seven million years ago. As humans and chimps gradually evolved from a common ancestor their DNA also changed by passing from generations to generations. Most of these changes in DNA had led to the difference between human and chimp appearance and behavior.

Complete answer:
Option A: Humans evolved from chimpanzees - Both humans and monkeys are primates. The humans are not descended from monkeys or any other primates which are living today. But the humans share a common ape ancestor with chimpanzees. Since humans did not evolve from chimpanzees.
So, option A is not correct.
Option B: Humans and chimpanzees share a relatively recent common ancestor - Chimpanzees and humans share a common ancestor commonly known as the chimpanzee - human last common ancestor (CHLCA). This is shared by the extant Homo and Pan genera of Hominini. The formation of hydrogen bonds or complementary base pairing when single stranded DNA from chimpanzee and humans are allowed to combine together, is over , meaning that chimpanzees are closest ancestors to humans. Hence option B is correct.
Option C: Chimpanzees evolved from humans - Chimpanzees did not evolve from humans. But humans and chimpanzees share a common ancestor.
Hence option C is not correct
Option D: Convergent evolution has led to similar nucleotide sequences in the two genomes - Most of the well-documented cases of convergent evolution of similar DNA sequence cases are usually restricted to a few amino acids. Hence it is not possible for convergent evolution to lead to similar nucleotide sequences in two genomes.
Hence option D is not correct.

So, Option B is the correct answer.

Note:
The human and chimpanzee immune systems are surprisingly similar. Most of the viruses that cause diseases like AIDS and hepatitis can also infect chimpanzees. But chimpanzees do not get infected by the malaria parasite Plasmodium falciparum, which a mosquito can transmit through its bite into human blood. A small DNA difference in humans makes human red blood cells vulnerable to this parasite, which chimp blood cells are resistant to.