Heredity and Variation

Heredity (heirship or inheritance) is the transmission of genetically based characters from parents to their offsprings.

Genetics is the branch of biology that deals with heredity and variation.​ Heredity refers to the transmission of genetically controlled traits from parents to offspring, while variation refers to the differences seen among individuals of the same species.​ These two ideas are central to understanding why living organisms resemble their parents but are not exactly identical.

Heredity and variation are not opposite ideas; they work together in living organisms.​ Heredity ensures continuity of species by passing traits from one generation to the next, while variation introduces differences that make each organism unique.

Without heredity, offspring would not resemble their parents.​ Without variation, populations would become too uniform, reducing their ability to adapt to changing conditions.

Variation is of two types: (i) Continuous variation and (ii) Discontinuous variation.

Continuous Variation:

Continuous variation shows a gradual range of small differences from one extreme to another.​ It usually involves traits influenced by multiple factors and is often represented as a smooth series.​

Examples

• Height in human beings.​
• Body weight.​
• Skin shade over a range.​

Discontinuous Variation:

Discontinuous variation shows clear-cut differences with distinct categories and no intermediate forms.​ Individuals fall into one group or another.​

Examples

• Blood groups in humans.​
• Ability to roll the tongue in textbook-style examples.​
• Attached or free earlobes in simplified school-level examples.

Variation has great biological importance because it helps populations survive and adjust over time. It provides the raw material on which natural selection can act.

• Variation makes individuals of the same species different from one another.​
• It increases the chance that some individuals will survive environmental changes.
• It supports adaptation and long-term evolution.
• It forms the basis of selective breeding in plants and animals.​
• It explains why useful traits can be chosen and maintained in breeding programmes.

• Genetics is the study of inheritance and variation in living organisms.
• Inheritance means passing traits from parents to offspring.
• Variation refers to differences between offspring and their parents.
• Early humans knew that sexual reproduction causes variation (around 8000–1000 B.C.).
• Humans used selective breeding to develop desirable traits (e.g., Sahiwal cows).