CBSE Class 10 Science Heredity And Evolution Notes Set 05

Heredity
Heredity refers to the transmission of characters from parents to offspring.

Inherited Traits: An inherited trait is a particular genetically determined feature that distinguishes a person from the others for example; attached or free ear lobes in human beings.

Rules for the inheritance of traits:
Mendel’s contribution: The rules for inheritance of traits in human beings are related to the fact that both mother and father contribute an equal amount of genetic material i.e. DNA to their offspring. So, an offspring will get two versions of that trait from the two parents. Mendel worked out rules for inheritance of these traits. Gregor Johann Mendel regarded as the ‘Father of Genetics’ performed his experiments with garden peas (Pisum sativum) in the garden behind his monastery Gene is the part of a chromosome which controls a specific biological function.

Contrasting characters: A pair of visible characters such as tall and dwarf, white and violet flowers, round and wrinkled seeds, green and yellow seeds etc.

Dominant trait: The character which expresses itself in a (Ft) generation is dominant trait. Example: Tallness is a dominant character in pea plant.

Recessive trait: The character which does not express itself but is present in a generation is recessive trait. Ex. dwarfism in the pea plant.

Homozygous: A condition in which both the genes of same type are present for example; an organism has both the genes for tallness it is expressed as TT and genes for dwarfness are written as tt.

Heterozygous: A condition in which both the genes are of different types for example; an organism has genes Tt it means it has a gene for tallness and the other for dwarfness only tall character is expressed.

Genotype: It is genetic makeup of an individual for example; A pure tall plant is expressed as TT and hybrid tall as Tt.

Phenotype: It is external appearance of the organism for example; a plant having Tt composition will appear tall although it has gene for dwarfness.

Law of Dominance: When parents having pure contrasting, characters are crossed then only one character expresses itself in the Ft generation. This character is the dominant character and the character/factor which cannot express itself is called the recessive character.