Study Notes on Evolution and Lactose Persistence

Key focus on the mechanisms of evolution and natural selection
Introduction of phylogenetic trees, which visually represent evolutionary relationships

Definition: Lactose intolerance is a common condition where individuals lose the ability to digest lactose, a sugar primarily found in milk.
Personal anecdote mentioning dislike for milk.

Lactose: A sugar consisting of glucose and galactose.
- Chemical structure:
- Involved in energy storage.

Lactase: Enzyme responsible for breaking down lactose into glucose and galactose.
- Location: Small intestine.
- Lactase is essential as glucose from lactose becomes the body's main energy source as well as playing critical roles in neural and immunological processes.

Lactase Tolerant: Individuals who continue to produce lactase into adulthood.
Lactase Intolerant: Individuals whose lactase production significantly decreases after weaning.

When lactose is not digested:
- Bacterial fermentation occurs in the large intestine, leading to gas and acids production.
- Symptoms include flatulence and abdominal pain.

LCT Gene: Gene that encodes for lactase enzyme.
- Regulation: Changes in diet can affect expression of the LCT gene.
- Despite the capability to digest lactose, the default condition for most mammals and humans is lactose intolerance.

Variation: 0-100% prevalence in different populations, depicted in a Lactose Intolerance Map.
- Map Overview: Percentages showing lactose intolerance prevalence across global regions.

Dairy Diaspora:
- The spread of dairying in human cultures began with the Neolithic transition:
- 11,000-10,000 years ago: Development of agriculture and possibly domestication of dairy animals.
- 8,400 years ago: Neolithic life spreads to Greece.
- 8,000 years ago: Neolithic reaches the Balkans.
- 7,500 years ago: Dairy economy established in central Europe.
Emergence of lactase persistence about 7,500 years ago in Central Europe correlates with these early dairy practices.

Lactase persistence has arisen multiple times within human populations, increasing in frequency.
Example sequences of lactase gene variants:
- Original allele and variations found in different populations:
- Europe: $(…AAGATAATGTAGTCCCTG…)$ (T-13910)
- Kenya: $(…AAGATAAGGTAGCCCCTG…)$ (G-13915)

Number of individuals identified as lactose tolerant versus those with mutations in the MCM6 gene associated with lactase persistence.
Phenomenon of directional selection enhancing lactose tolerance as these tolerant individuals interbreed.

Lactose intolerance as the baseline condition emphasizes the role of natural selection in shaping traits like lactose tolerance in specific environments.

Illustrate the mechanics of natural selection through examples such as disruptive selection in populations of mammals and their adaptation to diets.

Genetic factors influencing skin color and the involvement of melanin in this process.
Describe the function of melanin via keratinocytes and melanocytes.

Phylogenetic trees visually depict branches of evolution and shared ancestry, illustrating connections between species.
Importance of phylogenetic analysis in tracing disease evolution and family histories.

Discuss the role of DNA evidence in crime investigations, including famous cases like the Golden State Killer.
California Proposition 69: required collection of felon DNA samples to aid in criminal investigations.

Comparison of average household sizes worldwide, showcasing variances in living arrangements—highlighting cultural and geographic differences.

Explore how genetic ancestry services (like 23andMe and Ancestry.com) provide insights into familial connections and genetic traits, including shared ancestry.

Overall, genetic and evolutionary principles are reflected in human dietary habits, adaptations, and even familial relationships.

Phylogeny: The evolutionary history of a species or group of related species.
Clade: A group consisting of an ancestor and all its descendants.
Sister taxa: Two lineages that share a recent common ancestor.
Node: Represents a common ancestor on a phylogenetic tree.
Polytomy: A situation in phylogenetics where a single node gives rise to multiple branches (more than two).

Taxa: The plural form of taxon, representing a group of organisms at any level of classification.
Normalized distance: Involves distance measurement on phylogenetic trees to represent evolutionary time.

Applying principles of phylogeny and genetic analysis to understand evolution, genetic diversity, and the impact of environment on species adaptation.