Discontinuous variation

Discontinuous Variation refers to the variation seen in characteristics that can be categorized into distinct classes. Unlike continuous variation, where traits can exist along a continuum (e.g., height, weight), discontinuous variation involves traits that are clearly different from each other, with no intermediate forms. Examples of discontinuous variation include blood type, flower color in certain plant species, and the ability or inability to roll one's tongue. This type of variation is often controlled by a single gene or a small number of genes, making the inheritance patterns more straightforward than those of traits influenced by many genes.

Characteristics

Discontinuous variation results in a limited number of phenotypes with no intermediates. For instance, in pea plants, the flower color can be either purple or white, a classic example studied by Gregor Mendel. Mendel's work laid the foundation for the field of genetics, demonstrating how traits are inherited from one generation to the next. In humans, an example of discontinuous variation is the ABO blood group system, where individuals can have one of four blood types: A, B, AB, or O.

Genetic Basis

The genetic basis of discontinuous variation is typically straightforward, involving one or a few genes that follow Mendelian inheritance patterns. Each gene has two or more variants, known as alleles, and the combination of alleles an individual inherits determines their phenotype for a given trait. Dominant and recessive alleles play a significant role in these patterns, with dominant alleles masking the effect of recessive alleles in heterozygotes.

Importance in Evolution

Discontinuous variation is important in the study of evolution because it can lead to speciation, the formation of new species. When a population is divided, and different traits become advantageous in different environments, natural selection can increase the frequency of those traits. Over time, this can lead to the emergence of new species. Discontinuous traits that are easily observable (e.g., flower color) can be used by researchers to track evolutionary changes.

Examples

• Blood Type - Human blood types are an example of discontinuous variation, with four main types determined by the presence or absence of certain antigens.
• Pea Flower Color - The color of pea flowers, either purple or white, is determined by a single gene with two alleles.
• Tongue Rolling - The ability to roll the tongue is another example, controlled by a single gene with two alleles, where the ability to roll the tongue is dominant over the inability.

See Also

• Continuous Variation
• Genetics
• Mendelian Inheritance
• Evolution
• Speciation