Inheritance

How much alike are we to each other?

How are genetic traits passed along?

A. Patterns of Inheritance

  1. Phenotype: observable traits

    1. Feather color in Parakeets
    2. Mendel's pea garden observations
      • Inheritance of traits follows strict patterns
      • Multiple forms of genes exist for each trait
      • Individuals have 2 "heritable factors" per trait
      • Egg and sperm (pollen) each contribute 1 factor
      • Dominant and recessive traits exist
    3. Examples of Mendel's crosses
      • The Punnett square
      • F1 and F2 generation
  2. Genotype: gene combinations

    1. Different forms of the same gene exist = alleles
    2. Alleles are carried on homologous chromosomes
    3. Sperm and egg only contribute 1 homologue = 1 allele per trait
    4. Phenotype is determined by the combination of 2 alleles
      • Homozygous: both alleles same (PP or pp)
      • Heterozygous: 2 different alleles (Pp)
  3. Principles of Inheritance
    1. Segregation of alleles: homologous chromosomes
      • parental generation
      • F1 generation
      • F2 generation
      • Rules of probability!
    2. Independent assortment: for traits on different  chromosomes
      • Inheritance of trait A does not affect inheritance of trait B
      • AaBb x AaBb yields 9:3:3:1 ratio of phenotypes
    3. Genetic Linkage
      • Inheritance of traits A and B is linked
      • AB stay together and ab stay together
      • AaBb x AaBb yields 3:1 ratio of phenotypes
    4. Incomplete (partial) dominance
      • Heterozygotes have a unique phenotype
      • Aa xAa yields 1:2:1 ratio of phenotypes
    5. Codominance
    6. Pleiotropy
      • One gene has multiple phenotypic effects
      • e.g. syndromes (sickle cell, Marfan's, CF)
    7. Multiple gene traits: 
    8. Epistasis
      • Two genes interact to determine phenotype
      • AaBa x AaBb yields 9:3:4 ratio of phenotypes 
      • Model: white --> brown --> black
    9. Environmental influence on inheritance

B. Human Genetics

  1. Heritable human disorders
  2. Human Blood type system
  3. Gender determination: sex chromosomes
  4. Sex-linked traits
Why are more men color-blind than women? 
Are there any Y-linked traits?

Revisiting the Origins of genetic diversity

  1. Random assortment of chromosomes
  2. Crossing over
  3. Random fertilization
Applications
  1. Prenatal testing for heritable diseases
  2. Heritable diseases
  3. Pedigrees