Bihar Board - Class 12 Biology - Chapter 7: Evolution Short Answer Question

Q.1. What is the precondition for adaptive radiation?

A.1. The pre-condition for adaptive radiation is forming physical and geographical barriers between the population of the same species.

Q.2. What is the founder effect?

A.2. The founder effect is a type of genetic drift  which occurs when a few individuals in a population separate from the original population and form a colony. The genetic diversity of this new population will not be the same as that of the original population. This is a gradual process.

Q.3. What is the bottleneck effect?

A.3. The bottleneck effect is a type of genetic drift that occurs when the size of a population is severely reduced due to events such as earthquakes, epidemics, floods, fire, etc. In this process, a large number of organisms are deceased leaving behind only a handful of the population. Now, the genetic diversity of the surviving population becomes the genetic diversity of the entire population.

Q.4. What is natural selection?

A.4. Natural selection is the process in which the survival and reproductive rate of individuals with certain characteristics are greater than that of the other individuals in a population. This process leads to an evolutionary change.

Q.5. What are the factors affecting the Hardy-Weinberg equilibrium?

A.5. The factors affecting the Hardy-Weinberg equilibrium are:

• Genetic Recombination

• Gene Flow

• Genetic Drift

• Natural Selection

• Mutation

Q.6. What are the various stages of evolution?

A.6. There are seven stages of human evolution:

1. Dryopithecus

2. Ramapithecus

3. Australopithecus

4. Homo Erectus

5. Homo Sapiens Neanderthalensis

6. Homo Sapiens Sapiens

Q.7. What do you mean by “survival of the fittest”?

A.7. The term “survival of the fittest” was coined by Darwin in support of his theory of natural selection. The organisms that adapt to the changing environmental conditions and overcome the competitions for food and space are selected by nature to survive. In simple terms, the organisms that are physically in good shape and health are considered “fit”. The ones that aren’t are eliminated. This is known as “survival of the fittest”.

Q.8. Comment on the statement, “Migration may increase or decrease the effects of selection”.

A.8. Migration is the movement of individuals from one place to another. The individuals can either move to a different population or move into a particular population. Movement of individuals to a different population might remove certain alleles that confer better adaptations. Movement into a particular population might add certain alleles that blur the effects of selection. Thus we can say that migration can increase or decrease the effects of selection.

Q.9. How is nascent oxygen toxic to aerobic living organisms?

A.9. Nascent oxygen is very reactive and can react with all types of biomolecules present in living organisms, such as DNA, proteins and enzymes. It can cause mutation in DNA and can degrade proteins and enzymes on reactions, hence, toxic to aerobic life forms.

Q.10. Creation and presence of variation are directionless, but natural selection is directional as it is in the context of adaptation. Comment.

A.10. Variation is considered directionless because it is spontaneous and random. It is seen in sexually reproducing organisms which occurs as a result of crossing over during meiosis or fusion of gametes. The variations which help the individuals in adapting to the environment are passed on to successive generations. Natural selection is directional because it leads only to one path, i.e., selection. It is an evolutionary change that leads to the survival of the fittest and elimination of the unfit individuals.

Q.11. Comment on the statement with reference to industrial melanism, “Evolution is apparently reversible”.

A.11. The peppered moth resided on the surface of the lichens and protected itself from the predators due to camouflage. During industrialization in Europe, the surface of the lichens turned black due to the emissions from the coal-based industries. The moths were now easily visible to the predators and got eliminated gradually. A mutant of peppered moth flourished during this period. It was not visible to the predators due to its black color and hence was selected by nature. Clean air legislation was passed in Europe in 1956 as a result of which the emission of smoke decreased. The non-melanic peppered moth is appearing again along with the lichens. This proves that evolution is reversible.

Q.12. What is genetic drift?

A.12. Genetic drift is a mechanism of evolution in which the allele frequencies change over generations as a matter of chance. It occurs in populations of all sizes but its effect is the maximum in a small population. Genetic drift is observed when there is a sudden decline in the population due to natural disasters (bottleneck effect), or when a new population separates from the original population to form a colony (founder effect). Genetic drift does not take into account whether the allele is beneficial or harmful to the individual carrying it. It is possible that a beneficial allele is lost and a harmful allele persists.