Question

Explain how artificial selection has led to so many variations in dog breeds.

Describe how the process of natural selection causes evolution.

Answer 1

(A) Artificial selection, also called "selective breeding”, is where humans select for desirable traits in agricultural products or animals, rather than leaving the species to evolve and change gradually without human interference, like in natural selection.

1)Artificial selection was used to create 400-plus dog breeds. The effects of this selection on the dog genome can be observed when we compare different breeds to one another.

2)One example is leg length. Some breeds are defined by an unusually short leg without a proportional reduction in body size, such as in basset hounds and dachshunds. This trait is known as “chondrodysplasia.

3It was selected based on its utility for certain hunting roles, such as the pursuit of burrowing animals. The genetic basis of this trait turns out to be another duplication event that happened once within domestic dogs,all short leg breeds share the same genetic innovation.

4)The new gene is a processed pseudogene that acquired a function at the time of its duplication. Since the new copy was functional from the beginning, it is not best described as a pseudogene, but rather as a retrogene: the mRNA copy of a gene that was (a) reverse transcribed from mRNA back into DNA, (b) inserted into the genome next to sequences that could direct its expression, and (c) came under selection to maintain it.

(B) Natural selection leads to evolutionary change when individuals with certain characteristics have a greater survival or reproductive rate than other individuals in a population and pass on these inheritable genetic characteristics to their offspring.

Darwin's conclusions:-
1)In a population, some individuals will have inherited traits that help them survive and reproduce . The individuals with the helpful traits will leave more offspring in the next generation than their peers, since the traits make them more effective at surviving and reproducing.

2)Because the helpful traits are heritable, and because organisms with these traits leave more offspring, the traits will tend to become more common in the next generation.

3)Over generations, the population will become adapted to its environment as individuals with traits helpful in that environment have consistently greater reproductive success than their peer.

Example:

In the beginning there were two types of mice i.e tan ones and black ones.Hawks can see and catch the tan mice easily on the other hand black mice were caught less as their colour resembles the ground colour.So in the surviving population of mice the number of black mice is more.After several generations the tan mice may disappear.It is an example of natural selection causing evolution.