Question

Artificial selection to obtain cows yielding higher milk output represents
A. Stabilizing followed by disruption as it stabilizes the population to produce higher yielding cows.
B. Stabilizing selection as it stabilizes this character in the population.
C. Directional as it pushes the mean of the character in one direction.
D. Disruptive as it splits the population into two, one yielding higher output and the other lower output.

Answer 1

Hint:You should know, Selective breeding is also referred as artificial selection, and is process by which humans use plant and animal breeding to selectively make some specific phenotypic traits or characters by choosing which typically plant or animal males and females will sexually reproduce and will have offspring together. Two pure breed animals which differ in breeds give a crossbreed, and crossbred plants are referred as hybrids

Complete answer:
Let’s look at directional selection (also called positive selection), as a mode of natural selection in which an extreme phenotype is chosen over other phenotypes, which will cause the allele frequency to shift over time in that particular phenotype direction. In directional selection, the advantageous allele is increased as a consequence of differences in survival and reproduction amongst different phenotypes. These increases are not dependent on the dominance of the allele and even if the allele is recessive, it will become fixed. It’s interesting to know that the Directional selection was first told by Charles Darwin, in the book named- On the Origin of Species as a form of natural selection. And other types of natural selection comprises, stabilizing and disruptive selection. In both type of selection, are present same principles, but slightly differs as in, Disruptive selection-it favors both extreme phenotypes, different from one extreme in directional selection and whereas in, Stabilizing selection- it favors the middle phenotype, causing the decline in variation in a population over time.
Now let’s recap, directional artificial selection is a natural selection, where an extreme phenotype is favored over other phenotypes, this causes the allele frequency to shift with time in the direction of that phenotype. Remember, in order to get the cow yielding higher milk, the directional selection is used because it pushes the mean of the frequency of the selected individual towards one direction.

Additional information:
Note that, the deliberately done exploitation of selective breeding to produce desired results has become very common in agriculture and experimental biology.

Therefore, the correct answer is option C

Note:- Always keep in mind, that Artificial selection can be unintentional, e.g., resulting from the process of human cultivation but, it may also produce unintended undesirable or desirable results. As an example, in some grains, an increase in seed size may have been resulted from ploughing practices rather than by intentional selection of larger seeds.