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
  1. Prenatal testing for heritable diseases
  2. Heritable diseases
  3. Pedigrees