The TAS2R38 gene encodes a receptor protein that influences the ability to taste bitterness. The gene has two alleles: a dominant, wild-type allele that enables an individual (taster) to taste bitterness and a recessive, mutant allele that interferes with the ability of an individual (nontaster) to taste bitterness. Three single nucleotide mutations in the coding region of the TAS2R38 gene are associated with the nontaster allele. The nucleotides present at the three positions are shown in the table below.

Nucleotide Variation in the TAS2R38 Gene
Position in the Nucleotide Sequence
145 785 886
Human nontaster G T A
Human taster C C G
Bonobo C C G
Chimpanzee C C G
Gorilla C C G

A cladogram representing the evolutionary relatedness of selected primates is shown below.

From left to right, the branches are as follows: Orangutan, Gorilla, and Chimpanzee. Past the branches, the main line is labeled Human. Another branch, labeled Bonobo, is connected to the Chimpanzee branch.

Toxic substances often have a bitter taste that causes animals who try to eat such substances to spit them out rather than swallow them. Additional data suggest that gorilla populations have a very low frequency of nontasters.

Which of the following best describes the likely evolution of the TAS2R38 locus in the gorilla population?

Question

The TAS2R38 gene encodes a receptor protein that influences the ability to taste bitterness. The gene has two alleles: a dominant, wild-type allele that enables an individual (taster) to taste bitterness and a recessive, mutant allele that interferes with the ability of an individual (nontaster) to taste bitterness. Three single nucleotide mutations in the coding region of the TAS2R38 gene are associated with the nontaster allele. The nucleotides present at the three positions are shown in the table below.

Nucleotide Variation in the TAS2R38 Gene
	Position in the Nucleotide Sequence
	145	785	886
Human nontaster	G	T	A
Human taster	C	C	G
Bonobo	C	C	G
Chimpanzee	C	C	G
Gorilla	C	C	G

A cladogram representing the evolutionary relatedness of selected primates is shown below.

From left to right, the branches are as follows: Orangutan, Gorilla, and Chimpanzee. Past the branches, the main line is labeled Human. Another branch, labeled Bonobo, is connected to the Chimpanzee branch.

Toxic substances often have a bitter taste that causes animals who try to eat such substances to spit them out rather than swallow them. Additional data suggest that gorilla populations have a very low frequency of nontasters.

Which of the following best describes the likely evolution of the TAS2R38 locus in the gorilla population?

BlackTom AI · Accepted Answer

Natural selection favors alleles that increase an individual's chance of surviving long enough to reproduce. The TAS2R38 data show gorillas have the C–C–G nucleotide pattern at the three key positions — the same pattern seen in bonobo, chimpanzee, and the human taster — whereas the human nontaster has a different set (G–T–A). This indicates the taster allele (C–C–G) is the ancestral and common form in apes, and the nontaster (G–T–A) is a derived mutant found in some humans.

Step-by-step reasoning:
1. Compare sequences: gorilla = C C G, other great apes (chimp, bonobo) = C C G, human taster = C C G; human nontaster = G T A. Thus gorillas retain the ancestral taster genotype.
2. Observe population data: gorilla populations have a very low frequency of nontasters, implying the taster allele is common and nontaster alleles are rare.
3. Link phenotype to fitness: bitter taste receptors help detect toxic compounds in plants/food; individuals who can taste bitterness are more likely to reject toxic items, reducing poisoning risk and increasing survival.
4. Evolutionary inference: because tasters would have higher survival and reproductive success in environments with toxic foods, natural selection would favor the taster allele, keeping nontaster alleles at low frequency.

Why the correct answer fits: "Gorillas who could taste bitter toxins were more likely to survive and reproduce than nontasters" directly explains the high frequency of the taster allele via positive selection (or purifying selection against deleterious nontaster mutations).

Why other options are incorrect:
- Horizontal gene transfer is extremely unlikely between vertebrates and unnecessary here; shared sequence is ancestral, not transferred.
- Claim that tasters became resistant so the gene was no longer under selection contradicts the low frequency of nontasters (which indicates continued selection for tasters).
- The idea that tasters could utilize food resources nontasters could not is inconsistent with bitter taste typically deterring consumption of potentially toxic items rather than enabling new food use.

Conclusion: The best explanation is that tasting bitterness increased gorilla survival and reproductive success, matching the provided correct answer.

类似问题

Of all the factors that can disrupt Hardy-Weinberg equilibrium, ______ is the only one that can change a population to be better suited to its environment.

In Darwinian terms, the fittest individuals of a species are those that

Which of the following is probably the best explanation for the fact that Antarctic penguins cannot fly, although there is evidence that millions of years ago their ancestors could do so?

In Darwinian terms, the fittest individuals of a species are those that

Which of the following principles is NOT part of Darwin’s theory of evolution by natural selection?

In evolutionary terms, which of the following organisms is the most successful?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单