Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
According to Charles Darwin, evolution occurs through small, continuous variations that are directional and lead to gradual changes over generations.
Hugo de Vries proposed the Mutation Theory based on his work on the evening primrose ( ), suggesting that mutations are the primary cause of evolution.
Mutations are defined as sudden, random, and directionless changes in the genetic material (DNA).
De Vries coined the term 'Saltation' to describe a single-step large mutation that can lead to the formation of a new species.
In modern synthetic theory, variation is caused by multiple factors: gene mutations, chromosomal aberrations, genetic recombination during meiosis ( ), and gene flow.
While Darwinian variations are small and directional (leading to gradualism), mutations are large and random (leading to saltation).
📐Formulae
💡Examples
Problem 1:
Explain the molecular basis of the mutation that causes Sickle Cell Anemia as a mechanism of variation.
Solution:
A point mutation occurs in the -globin chain of hemoglobin. The triplet codon (coding for Glutamic acid) is mutated to (coding for Valine) at the position.
Explanation:
This single base substitution () results in a structural change in the molecule under low oxygen tension, leading to the sickling of . This represents a hereditary variation caused by mutation.
Problem 2:
Contrast Darwinian variation with Hugo de Vries' mutation concept in a population of size .
Solution:
Darwinian variation: Small, directional, and leads to gradualism. Mutation: Large, random, directionless, and leads to saltation.
Explanation:
Darwin believed that evolution was a slow, continuous process, whereas De Vries believed that a single large mutation could cause speciation () instantly without intermediates.