Darwin's Missing Link: Genetics & Epigenetics

What Darwin didn’t know…particulate inheritance

• Darwin used “blending” to explain heredity/inheritance (weak)

• 1866: Gregor Mendel’s experiments/ideas on particulate inheritance published - “Experiements in Plant Hybridation”

  • offspring aren’t blends of parents, but receive indivisible units of heredity (we now call genes)

  • significance of his work was obscure for about 30 years

Genotypes & Phenotypes

• genotype: entire collection of genes an individual possesses

• phenotype: expressed or “on” genes behind traits the individual possesses

• for alleles, individuals can be homozygous (same gene form in each pair) or heterozygous (different versions of gene)

• may alleles have dominant or recessive members of gene pairs that determine phenotypic traits

Frrom genes to traits

• polygenic traits: “multiple genes affect one trait”

  • e.g., skin color (3 genes)

• pleiotropy: “one gene affects multiple traits”

  • e.g., phenylketonuria (PKU) from gene mutation (chromosome 12) can affect growth, temperament, IQ

This would blow Darwin’s mind…Deep genetic ancestry

• hox genes: fundamental ways the body get built

  • controls how bodies form

  • Different species can have same set of genes → but are modified

Deep Ancestry: Homeobox (“Hox”) genes

• hox genes: have been around for billion yrs but have been carried on through different species & still do fundamental job

Heritability Estimates for Human Physical Traits

• physical has strong genetic ability

  • eye color is the most

  • BMI is 2nd

  • Height is 3rd

  • Athletic ability is last

• personality

  • OCEAN has strong top 5

  • lots of psych traits have genetic component

    • variation is present

    • how strong?

Epigenetics: Rainbow & C.C.

• color variation differred

Epigenetics

• Epigenetics can be defined as “any heritable influence on gene activity that does not involve a change in DNA sequence”

  • involves expression of genes

Epigenetics: Histones & Methylation

• methylation → makes DNA wrap tight around histones => down-regulates genes

Epigenetics: Agouti = Big Booty; epigenetic effect from mother’s diet

• what mother ate → adding methyl group → silences agouti gene

• aka what mom ate changed expression of offspring genes

Epigenetic effect from grandmother’s diet

• what grandmother ate altered expression of grandchildren mice (aka 2 generations later)

  • from 80% → 60%

• epigenetics are transgenerational

  • not changing DNA, but changing expression of genes

Epigenetics: The Overkälix Studies

• grandson’s mortality risk ratio:

  • baseline: 1.0

  • when harvest was poor = grandson’s died a lower

  • when harvest was good = grandson’s died at higher rate

  • → counterintuitive = maybe change in response to survival

• something beyond DNA is passing on & affecting health based on grandfather during sexual maturity