DAT Question of the Day

Correct Answer: C. a nonsense mutation

A silent mutation often occurs in the wobble site of the codon on the mRNA strand. For most codons, if the third base pair is changed, the correct amino acid can still be made. A missense mutation results in the addition of an incorrect amino acid, but can still lead to a functional protein. Nonsense mutations result in a polypeptide chain that is shorter and is non-functional. For nonsense mutations, an insertion or deletion of a nucleotide base creates a premature stop codon (UGA, UAG, or UAA), terminating translation before the polypeptide can be completed. Transfer mutation is not an accurate term in biology.

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Correct Answer: A. Two squirrel populations separated by a river

In allopatric speciation, two species result due to the geographical barrier between the two species. Two birds living in different parts of the tree may result in two separate species over time, if the birds have different mating rituals or mating seasons. This would not be due to a geographical barrier and would be an example of sympatric speciation. Lion prides could still reproduce with one another especially since they inhabit the same area and climate. Insects with the same mating call would interbreed and this would not result in two different species over time. Similarly, two groups of dogs with different fur color should still be able to reproduce. However, two squirrel populations separated by a river may evolve into two different species over time, as the squirrels may be inhabiting different environments and are separated by the body of water.

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Correct Answer: A. radial

Spiral cleavage results in daughter cells after cell division, being located at an angle in relationship to each other. This is common in protostomes. Whereas radial cleavage results in the daughter cells after cell division being stacked on top of each other. Radial cleavage is seen in deuterostomes.

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