BSC2010-evolution-4-2024 (2)

Processes of Evolution

Title: Processes of Evolution IAuthors: Shenghao Ye et al. 2024, PNAS BSC 2010, Fall 202

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Outline of Evolutionary Concepts

  • What evolves?

  • Heritable Units

  • Mendel’s Theory of Heredity

  • Microevolution Defined

  • Gene Pool Definition

  • Detecting Evolution in Populations

  • Hardy-Weinberg Equilibrium

What Evolves?

Focus on: Populations

Definition: A group of individuals of the same species living in the same area at the same time

Insight: Darwin understood the evolution of populations through natural selection but did not know the concept of heritable units.

Darwin’s Early Ideas on Heredity

Gemmules Concept: From his work, Variation of Plants and Animals under Domestication (1868)Described cells producing granules (gemmules) that convey inherited traits across generations.This explanation was eventually deemed incorrect.

Advancements from Gregor Mendel

Mendelian Genetics (1866):Developed theory of heredity, showingParents pass discrete, heritable factors (genes) to offspring, determining inherited traits.Key Concepts: Genes act in predictable ways, forming the basis of heredity.

Integration of Darwin and Mendel

Population Genetics:Merging of concepts from Darwin and MendelNatural selection acts on individuals; evolution occurs at the population level.Genes as units of heredity.

Understanding Alleles

Definitions:

  • Homozygous: Two identical alleles

  • Heterozygous: Two different alleles

  • Dominant Alleles: Expressed in phenotype; suppress recessive

  • Recessive Alleles: Not expressed in the presence of a dominant allele.

Microevolution Defined

Gene Pool:All genes in a population, including all alleles.Microevolution Characteristics:

  • Changes in genotype proportions within a population.

  • Altered allele frequencies over time.

Monitoring Population Evolution

Detecting Evolution:Measure allele frequencies across generations.Lack of change indicates equilibrium; population remains non-evolving.

Hardy-Weinberg Theorem

Key Formula:In a two-allele system:p + q = 1 (where p = frequency of dominant, q = frequency of recessive allele)Frequency calculations based on genotypes follows: p² + 2pq + q² = 1 (predicts next generation's genotype frequencies).

Genetic Equilibrium and Its Implications

Equilibrium Indicators:Frequency of alleles remains stable across generations.If allele frequencies match H-W predictions, the population is not evolving for that trait.

Factors Affecting Genetic Equilibrium

Causes of Microevolution:

  • Mutation: Changes in genetic material

  • Gene Flow: Movement of alleles between populations

  • Genetic Drift: Random fluctuations in allele frequencies

  • Nonrandom Mating: Selective patterns in mating

  • Natural Selection: Differential survival and reproduction based on genotype.

Population Genetics Definitions

  • Genotype: Genetic constitution of an individual.

  • Phenotype: Observable traits determined by genotype.

  • Gene: The unit of heredity; the basis of phenotype.

  • Allele: Variants of a gene.

Example of Alleles in Plants

Color Genetics:R = dominant allele, r = recessive alleleVarious combinations include homozygous dominant (RR), heterozygous (Rr), and homozygous recessive (rr).