Question

Ascorbic acid (vitamin C) is an organic molecule necessary for the health of plants and animals. The majority of animals, including most mammals, synthesize ascorbic acid from organic precursors, but some primates are unable to synthesize ascorbic acid and must instead acquire it from dietary sources, such as certain fruits and vegetables. The L- gulonolactone oxidase (GULO) gene encodes an enzyme that catalyzes a required step in the biosynthesis of ascorbic acid. Most mammals carry a functional copy of the GULO gene, but some primates carry only a GULO pseudogene, which is a nonfunctional variant. A comparison of GULO genes and GULO pseudogenes from different animals can provide insight into the evolutionary relatedness of the animals. In Table 1, selected members of some mammalian groups are listed, along with an indication of their ability to synthesize ascorbic acid. Table Il shows an alignment of amino acid coding sequences from homologous regions of the GULO genes and GULO pseudogenes of the organisms listed in Table 1. Figure 1 represents the universal genetic code. TABLE : SELECTED MAMMALIAN GROUPS Biosynthesis of Selected Members Group Ascorbic Acid Nonprimate mammals Elephant, mouse Primale mammals Orangutan, chimpanzee mur I luman TABLET DNA SEQUENCE ALKINMENT Het Position ATCIT AGA SAATUAGGA ides in the tripleted the template coding and A n icates the Fresh DNA w el, the acting shaded and pen reading freshen me right of a no shared the

Answer 1

Non-primates and Lemurs can synthesize ascorbic acid from its organic precursors. But some primate mammals i.e. orangutans, chimpanzees and humans cannot do the same because of the mutation in GULO gene. So, it is clear that mutation of GULO gene occurred in the most recent common ancestor (MRCA) of orangutans, chimpamzees and humans. The phylogenetic tree in option-A clearly indicates that the mutation (denoted by 'X') occurred in most recent common ancestor of orangutans, chimpamzees and humans.

Option-B is incorrect because it is showing that the mutation occurred in MRCA of Lemurs which is false.

Option-C is incorrect because it is showing that the mutation occurred in MRCA of non-primates but Lemurs being a primate have the functional copy of GULO gene. So it is false.

Option-D is incorrect because it is showing that the mutation occurred in MRCA of all the primates and non-primates. So, it is false.

Option-A is the correct answer.