State that discontinuous variation results in a limited number of phenotypes with no intermediates; examples include ABO blood groups, seed shape in peas and seed colour in peas

Discontinuous variation refers to the type of variation in which individuals within a population exhibit distinct phenotypes with no intermediates. This results in a limited number of discrete categories rather than a continuous range of traits.

Characteristics of Discontinuous Variation

• Distinct Phenotypes: Individuals can be classified into clear categories based on specific traits, with no gradual transitions between these categories.
• Influence of Single Genes: Traits that display discontinuous variation are often controlled by single genes (or a small number of genes), leading to distinct phenotypic expressions.

Examples of Discontinuous Variation

1. ABO Blood Groups
   • Human blood types are classified into four distinct groups: A, B, AB, and O. There are no intermediate blood types, illustrating clear categories based on the presence or absence of specific antigens.
2. Seed Shape in Peas
   • In pea plants (Pisum sativum), seed shape can be either round or wrinkled. This trait is determined by a single gene, resulting in two distinct phenotypes without any intermediate forms.
3. Seed Colour in Peas
   • Similarly, pea seeds can be yellow or green, again reflecting a clear distinction with no intermediate colors. This trait is also governed by a single gene.