The given question involves understanding the concepts of synonymous and non-synonymous substitution in evolutionary biology and interpreting what it means if the rate of one exceeds the other. Let's break it down:
- Understanding Synonymous and Non-Synonymous Substitutions:
- Synonymous Substitution: This is a change in the DNA sequence that does not alter the amino acid sequence of a protein. Thus, it is often considered neutral in terms of selection.
- Non-Synonymous Substitution: This is a change in the DNA sequence that results in a change in the amino acid sequence of a protein. Such changes can affect the function of a protein and are subject to selective pressures.
- Analyzing the Rates:
- If the rate of non-synonymous substitution exceeds that of synonymous substitution, it suggests that changes in the protein sequence are advantageous and being favored by natural selection.
- In typical scenarios, synonymous substitutions occur more frequently because they are usually neutral. Non-synonymous substitutions being more frequent indicate positive selection pressure.
- Evaluating Options:
- Deleterious mutations are accumulating: This is unlikely because deleterious mutations tend to decrease fitness and are not positively selected for.
- Evolution is not occurring: This is incorrect because substitution rates being non-neutral indicate ongoing evolution.
- Genetic drift is operating: Genetic drift is a random process, whereas the scenario described involves selection, which is not random.
- Selection is operating: This is correct, as the excess of non-synonymous substitutions suggests positive selection for advantageous traits. Hence, this is the correct answer.
In conclusion, when the rate of non-synonymous substitution at a locus exceeds that of synonymous substitution, it indicates that selection is operating.
Important Questions from Natural selection
Aphids feed on both alfalfa and clover plants. A researcher collected and reared different genotypes of aphids from separate alfalfa and clover fields. He then measured the fecundity of both aphid groups when fed on each of the two host plants. The figure summarizes the performance of aphid groups originating from alfalfa (dashed) or clover (solid).
Which one or more of the following situations does the figure depict?- Which one or more of the following conditions is/are necessary for the evolution of increased nectar production in an insect-pollinated plant via natural selection?
There are two species, X and Y, with abundances $x$ and $y$, respectively. Species X has growth rate $\alpha$, and species Y has growth rate $\beta$. Assume that the sum of the species abundances is constant over time, i.e., $x + y = 1$. Let $x$ and $y$ follow the rate equations:
$$\frac{dx}{dt} = \alpha x - \varphi x,$$
$$\frac{dy}{dt} = \beta y - \varphi y,$$ where $\varphi$ is the average species fitness.
Which one of the following options correctly represents the expression for $\varphi$?The figure illustrates the soil zinc tolerance of the grass species Anthoxanthum along a transect from inside a mine to the middle of a pasture outside the mine.
Which one or more of the following processes explain(s) the observed pattern of zinc tolerance in this grass species?A researcher estimates the relationship between reproductive success ($N$, number of offspring) and horn length ($H$, in cm) in a wild goat as
$N = 40 – 2.2H + 0.04H^2$
Horn length typically varies from 10 cm to 50 cm in this species. Which one of the following graphs correctly represents this relationship?
