TF

HERITABILITY

Heredity and Variation

  • Key Concepts: Mutation, inheritance, and the modern synthesis
  • Outline:
  • Inheritance of traits
  • Discrete vs. Continuous variation
  • Mendel's experiments
  • Mendelians vs. Biometricians
  • The Modern Synthesis

Variation in Genetics

Discrete Variation

  • Definition: Variation in qualitative traits that fall into distinct categories.
  • Human Examples:
  • Tongue rolling
  • Attached ear lobes
  • Widow's peak
  • Hitchhiker's thumb

Continuous Variation

  • Definition: Variation in quantitative traits that fall along a numerical continuum.
  • Human Examples:
  • Height
  • Skin Color
  • Body Mass
  • Number of fingerprint ridges

Inheritance of Traits: Historical Perspective

Major Questions in Darwin's Time

  1. Which tissues carry genetic information?
  2. How is genetic information passed on?

Key Terms

  • Germ line: Cells (gametes) that contribute genetic information through meiosis.
  • Soma: All other somatic tissues.

Theories of Heredity

  • Pangenesis Theory: Darwin's provisional mechanism; suggests all body parts contribute to gametes.
  • Germ Plasm Theory: Only gonads contribute genetic material to sex cells.

Blending Inheritance

  • Darwin's idea noted, leading to critiques of natural selection:
  • Favorable types may be lost across populations.
  • Small natural variation impacts selection.
  • Hugo de Vries' Mutation Theory: Rediscovered Mendelian inheritance in 1900; focused on mutation as a mechanism for evolution.

Evolution Mechanisms

  1. Darwin and Biometricians: Emphasized natural selection.
  2. De Vries and Mendelians: Emphasized mutations and discrete variation.

Mendelian Genetics

Mendel's Experiments

  • Conducted in 19th-century Czech Republic using Pisum sativum (pea plants).
  • Crossed plants with distinct traits over two years to track offspring characteristics.

Genetics Vocabulary

  • Gene: Unit of heredity.
  • Allele: Variant of a gene; can be dominant or recessive.
  • Locus: Location of a gene on a chromosome.
  • Genotype: Genetic makeup; can be homozygous (same alleles) or heterozygous (different alleles).

Mendel's Laws

  • Law of Segregation: Each gamete carries one allele for every trait.
  • Law of Independent Assortment: Alleles for different genes are inherited independently.

The Modern Synthesis

  • Timeframe: 1930s and 40s; integrated Mendelian genetics with evolution.
  • Macroevolution vs. Microevolution: Synonymous linkage of macroevolutionary patterns with microevolutionary processes as seen through genetics.
  • Codominance and Polygenic Traits: Shared effects of multiple genes on a single phenotype.

Key Factors

  • Mutation: Raw material for evolution; underpins adaptation through natural selection.
  • Gradualism: Emphasizes gradual change leading to macroevolution effects.

Natural Selection

  • Variation exists within traits of individuals, and this variation is inherited.
  • Survival and Reproductive Success: Influenced by genetic traits.

Important Mechanisms

  • Mutations: Create new alleles; reshuffle through segregation and independent assortment, leading to heritable variation.

Mutations: Types and Effects

  • Point Mutation / Insertion / Deletion: Alters allele formation.

  • Gene Duplication: Leads to potential new gene functions.

  • Genome Duplication: Can result in new species through significant genetic transitions.

  • Overall Impact: Essential in generating evolutionarily significant variation.