ACQUIRED AND INHERITED TRAITS Explained : NCERT Notes on Biology

ACQUIRED AND INHERITED TRAITS

  • A trait (or characteristic) of an organism which is ‘not inherited’ but develops in response to the environment is called an acquired trait.
  • For example, if a beetle does not get sufficient food for a considerable time, its weight will be reduced due to starvation.
  • The ‘low weight’ of this beetle is an acquired trait of the beetle which has been acquired in response to the environment which contained insufficient food.
  • The acquired traits of organisms cannot be passed on to their future generations
  • Only those traits can be transmitted to future generations in which changes have occurred in the genes (or DNA) present in the reproductive cells (or gametes) of parent organisms.
  • The changes in the non-reproductive body cells of an organism cannot be inherited by its offsprings.

Beetle Experiment

  • When the weight of a beetle is reduced too much due to starvation, then though there is a change in the normal body cells of the beetle but no change takes place in the genes (or DNA) present in its reproductive cells (or gametes).
  • And since there is no change in the genes (or DNA) of gametes, this acquired trait (of low weight) of beetles cannot be inherited by its offspring.

Inherited trait: A trait (or characteristic) of an organism which is caused by a change in its genes (or DNA) is called an inherited trait.

  • Inherited traits can be passed on to the progeny of the organism because they have produced changes in the genes (or DNA) of the organism.
  • Inherited traits actually mean the characteristics which we receive from our parents.
  • For example, a father has red curly hair, brown eyes, a snub nose and a cleft chin.
  • Again suppose that the mother has straight black hair, blue eyes, a long thin nose and a pointed chin.
  • The children in the family inherit some characteristics from each of their parents.
  • For example, two children have red hair like their father but one of them has straight red hair while the other one has curly red hair.
  • The two children have black hair like the mother.
  • Again, two children have brown eyes like father but the other two have blue eyes like the mother.
  • And finally, two children have snub nose and cleft chin like father whereas the other two have a long thin nose and a pointed chin.

SPECIATION

  • A species is a population of organisms consisting of similar individuals which can breed together and produce fertile offspring.
  • The process by which new species develop from the existing species is known as speciation.
  • In simple words, the formation of new species is called speciation
  • In most of the cases, new species are formed when the population of the same species splits into two separate groups which then get isolated from each other geographically by the barriers such as mountain ranges, rivers or the sea.
  • The geographical isolation of the two groups of population leads to their reproductive isolation due to which no genes are exchanged between them.
  • However, breeding continues within the isolated populations producing more and more generations.
  • Over the generations, the processes of genetic drift (random change in gene frequency), and natural selection operate in different ways in the two isolated groups of population and make them more and more different from each other.
  • Geographical isolation is the major factor in the speciation of sexually reproducing animals because it interrupts the flow of genes between their isolated populations through the gametes.

 

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