Genetics and Evolution Notes

Alleles

  • Alleles are different forms of a gene.
  • Example: Gene for eye color, alleles for brown, blue, green, or gray eyes.

Dominant vs. Recessive Alleles

  • Dominant allele: Only one copy needed for expression.
  • Recessive allele: Two copies needed for expression.

Genotype and Phenotype

  • Genotype: Combination of alleles at a locus (e.g., big A little a).
  • Homozygous: Two of the same alleles.
  • Heterozygous: Two different alleles.
  • Phenotype: Observable manifestation of a genotype (e.g., green eyes from big A little a genotype).

Dominance Types

  • Complete dominance: Only one dominant allele.
  • Codominance: More than one dominant allele is expressed.
  • Incomplete dominance: No dominant allele; expression can be mixed or partial.

Penetrance

  • Proportion of individuals with a specific allele who express the associated phenotype.
  • Example: Some people with an allele for a condition may not show the phenotype.

Expressivity

  • Variable phenotypic outcome of a genotype.
  • Example: Genotype for extra fingers can result in different numbers of fingers (e.g., six or nine).

Genetic Leakage

  • Flow of genes between species via hybrid offspring.

Genetic Drift

  • Changes in the composition of a gene pool due to chance.
  • Example: In a small population, one allele can dominate over time.

Founder Effect

  • When a small group establishes a new population, their genes become disproportionately common.
  • Leads to inbreeding.

Taxonomic Rank

  • Mnemonic: King Philip Came Over From Great Spain (Kingdom, Phylum, Class, Order, Family, Genus, Species)

Mendel's Laws

  • Law of Segregation: Two alleles for a gene separate during anaphase I of meiosis.
  • Law of Independent Assortment: Alleles of different genes assort independently of one another (not true for linked genes).
  • Linked genes: Genes located close together on the same chromosome are more likely to be inherited together.

Experiments Showing DNA as Genetic Material

  • Griffith's experiment: Demonstrated transformation; bacteria could pick up DNA from their environment.
  • Avery-MacLeod-McCarty experiment: Showed that degradation of DNA led to cessation of bacterial transformation while degradation of proteins did not, indicating DNA is the transforming factor.
  • Hershey-Chase experiment: Radio-labeled DNA was found in bacteriophage-infected bacteria, confirming DNA as genetic material.

Types of Evolution

  • Divergent, parallel, and convergent evolution.

Nucleotide Mutations

  • Point mutation.
  • Frameshift mutation.
  • Results:
    • Silent: No effect on protein.
    • Missense: One amino acid replaced by another.
    • Nonsense: Results in a stop codon, truncating the protein.

Frameshift Mutations

  • Insertion or deletion of nucleotides, altering the reading frame of mRNA.
  • Example: Adding 'A' to 'ATC' shifts the reading frame: 'AAT C'.

Results in Protein

  • Silent: No effect on protein.
    • Missense or Nonsense.
  • Insertion or Deletion: Insertion of an amino acid into the amino acid chain.

Chromosomal Mutations

  • Affect large segments of DNA on a chromosome.
  • Types: Deletion, duplication, inversion, insertion, translocation.

Analytical Techniques

  • Hardy-Weinberg Principle:
    • p + q = 1 (for two alleles)
    • p and q represent the frequencies of the two alleles.
    • Assumes stagnant population with no evolution.

Recombination Frequency

  • Likelihood of two alleles being separated during crossing over in meiosis.
  • Crossing over can swap alleles on the same chromosome.
  • Recombination frequency is related to the distance between genes; closer genes have lower recombination frequency.

Evolution

  • Natural selection: Primary mechanism for evolution.

Modern Synthesis Model

  • Mutation and recombination are mechanisms for variation.

Inclusive Fitness

  • Allele frequencies remain constant in the absence of environmental change and evolution.

Punctuated Equilibrium

  • Long periods of slow evolution followed by bursts of evolutionary activity.

Types of Natural Selection

Stabilizing, directional, disruptive, and adaptive.

Molecular Clock Model

  • The degree of genomic difference between two species is related to the time since they diverged from a common ancestor.
  • Species with a more recent common ancestor have more similar genomes.