Name the phenomenon that governs the following:
(i) Green beetles living in green bushes are not eaten by the crows.
(ii) Number of blue beetles in green bushes increases only because the red beetles, living there, were trampled by a herd of elephants.
(iii) No ‘medium height plants’ are obtained in F 1 generation, upon crossing pure tall and drawf pea plants.
(iv) Tails of mice were surgically removed for several generations, still mice had tails in the following generations.
(v) A migrant beetle reproduces with the local population; as a result genes of migrant beetle enter the new population.
(i) Natural Selection
It is the process of evolution of a species whereby characteristics which help individual organisms to survive and reproduce are passed on to their offspring , and those characteristics which do not are not passed on.
The green beetles camouflage on the green leaves and cannot be seen by crows, and hence they are not eaten by crows. Whereas, the population of red beetles is continuously declining.
(ii) Genetic Drift
Drastic changes in the frequencies of genes in a small population is called genetic drift.
The elephant stamping and, by chance, eradication of the red beetle population leaves only the blue beetle population.
Even though the blue color has no survival advantage, this accident in a tiny population caused a variance in the frequency of particular genes.
(iii) Law of Dominance
The law of dominance of traits states that “When parents having pure contrasting characters are crossed then only one character expresses itself in F1 generation . This character is the dominant character and the character which cannot express itself is called a recessive character ”.
When pure tall (TT) pea plants are crossed with pure dwarf (tt) pea plants, all the plants in the F 1 progeny are tall(Tt) .
The appearance of all Tall plants in the F 1 generation shows that tallness is the dominant character while dwarfness is the recessive character.
(iv) Acquired traits are not inherited
Acquired traits are the traits a person develops during his lifetime and they aren’t passed from one generation to the next.
Surgical removal of the tails of mice does not affect the germ cells of the mice. Only if there is a change in the germ cell, the trait will be passed onto the next generation.
(v) Gene flow
Gene flow is the transfer of genes from one population species to another . Gene flow occurs when the transfer of genes is followed by interbreeding.
When migrant beetles reproduce with local beetles, there is a transfer of genes and interbreeding taking place.