Week 8: The Allele for Cystic Fibrosis and Evolution

Vocabulary flashcards covering key terms from Week 8 notes on CF allele, TB, and evolution.

Cystic Fibrosis allele

A genetic variant that may be more common in some populations due to a potential protective effect against tuberculosis in carriers.

Tuberculosis (TB)

Infectious disease caused by Mycobacterium tuberculosis; ~2 billion people carry TB globally; ~1 new infection per second; ~2 million deaths per year; 90% infections are asymptomatic.

Mycobacterium tuberculosis

The bacterium that causes tuberculosis.

Tubercles

Nodules formed to contain bacterial colonies in the lungs.

Consumption

Old term for TB, reflecting the wasting and damage caused by prolonged infection.

TB Transmission

Spread through the air from infected individuals; a single sneeze can release up to 40,000 droplets.

Groups at highest risk

Young children, elderly individuals, and people with weakened immune systems.

TB treatment before antibiotics

Rural sanatorium care focusing on fresh air and isolation to limit spread.

TB treatment after antibiotics

Antibiotics since the 1940s; after 2 weeks, patients are no longer contagious; full treatment lasts 6–12 months.

MDR-TB

Multidrug-resistant TB; resistant to standard first-line antibiotics.

XDR-TB

Extensively drug-resistant TB; resistant to second-line drugs; cure rates are low.

KDR-TB

TB resistant even to second-line drugs.

Cystic fibrosis allele protection hypothesis

Observation that the CF allele is more common in some populations; hypothesis that it protects carriers from TB.

Prediction of CF-TB hypothesis

Populations with past TB epidemics would have a higher frequency of CF carriers after the epidemic.

Carrier frequency

Frequency of carriers in a population; calculated as the number of carriers divided by the total population.

Darwin’s Theory of Common Descent

All species descended from a single common ancestor; widely accepted within about 20 years of publication.

Natural Selection

Process by which traits that improve survival or reproduction become more common in a population over time; results from competition; a key cause of evolution.

Observation 1: Variation Within Populations

Variation exists within populations and can be inherited.

Observation 2: Heritable Variation

Some variations are inherited by offspring; genetics (rediscovery of Mendel) explain heredity.

Observation 3: Overproduction of Offspring

Populations produce more offspring than can survive, leading to competition for resources.

Observation 4: Non-Random Survival and Reproduction

Some individuals have advantageous traits; survival and reproduction are not random.

Fitness

Relative survival and reproductive success of a variant.

Adaptation

A trait that increases an individual's fitness in a particular environment.

Beak Size adaptation example

Larger beaks help cracking tough seeds during droughts; increased fitness and higher frequency of large-beaked birds.

Evolution

A change in the inherited traits of individuals in a population over generations.

Artificial Selection

Human-directed selection of individuals with preferred traits for reproduction.

Natural Selection in the Lab

Controlled experiments show how environmental conditions (e.g., varying alcohol) can favor certain traits over generations.

Natural Selection in Wild Populations

Real-world examples include antibiotic resistance in TB, beak size changes in Galápagos finches, and thicker shells in blue mussels against invasive predators.

Drug resistance and human health

Directional selection can occur when antibiotic treatment favors resistant bacteria.

MRSA

Methicillin-resistant Staphylococcus aureus; evolved from common skin bacteria into a dangerous pathogen due to antibiotic misuse.

Sickle-cell allele and malaria

In malaria-endemic regions, one sickle-cell allele increases fitness by reducing malaria parasite reproduction, maintaining the allele due to selective pressure.

Binomial Naming System

Two-part species name: Genus (capitalized) and species (lowercase); sometimes subspecies; developed by Linnaeus.

Genus

First part of the binomial name; broader group (e.g., Panthera).

Species

Second part of the binomial name; specific identity (e.g., leo).

Linnaeus Homo sapiens sapiens

Humans as the subspecies Homo sapiens sapiens.

Biological Species Concept

A species can interbreed and produce fertile offspring; cannot reproduce successfully with other species.

Difficulties applying BSC

Hard to apply to fossils and asexual organisms (e.g., bacteria).

Gene Pool

All the alleles present in individuals of a species.

Gene Flow

Spread of an allele across a species' gene pool; no gene flow between different species.

Reproductive Isolation

Pre-fertilization barriers prevent mating or fertilization; post-fertilization barriers result in hybrids that cannot reproduce (e.g., mule).

Mule

Infertile hybrid of a horse and a donkey; demonstrates a post-fertilization reproductive barrier.

Evolution of Reproductive Isolation

The precise moment two populations become separate species is unclear; examples include dragonflies and dogs.