Chapter 13.5: Selection Can Maintain Polymorphisms in Populations

Flashcards from Chapter 13.5 of Principles of Life, 3rd Edition.

Polymorphism

The presence of two or more variants of a character in the same population

• Natural selection often preserves variation in this way

Frequency-dependent selection

Selection that changes in intensity with the proportion of individuals in a population having the trait

• Seen with P. microlepis, which prey on fish from one side in equal numbers in order to preserve their distorted mouth characteristic in nature

Heterozygote advantage

The advantage of having two different alleles in an organism compared to having two of the same alleles due to greater adaptability to environments

• Seen with the Colias butterflies of the Rocky Mountains, due to their need to survive in cold and hot temperatures seasonally

Clinal variation

A pattern of gradual change in phenotype across a geographic gradient due to environmental changes

• Seen with T. repens clovers producing varying levels of cyanide due to European temperature differences making production hazardous in colder areas