Evolution and Its Mechanisms

Evolution

• Evolution affects populations (species) not just individuals, even though natural selection affects individuals.
• Evolution works on existing genetic traits that are already in a population. These traits do not develop because they are needed.
• Evolution can't predict the future.
• Pre-adaptations are characteristics that exist in a population and acquire a new function due to selection; working on existing variations.
• Pre-adaptation example: giant panda's sesamoid bone, modified for grasping bamboo.

Infanticide

• A male lion kills another male's cubs from a different pride, which causes the female to go into heat and reproduce with him.
• Causes more offspring for the male.

Gonopodia

• The longer the gonopodia (in fish), the more likely the fish is to find a mate.
• Longer gonopodia are more likely to catch food.
• Longer gonopodia are also detrimental to survival.

Mutations and DNA

• Mutations are not all bad, some are beneficial.
• Mutations are changes in the DNA that can lead to a new protein product.
• Mutations are key sources of variation for evolution.
• DNA consists of a sugar phosphate backbone.
• A + T pair (2 H bonds), C + G pair (3 H bonds)
• Phosphodiester bond links them together.
• DNA → mRNA → Protein
• Watson and Crick stole Rosalind Franklin's lab and discovered DNA.
• Kornberg figured out how DNA replicates.

Sickle Cell Anemia

• This disease occurs due to a mutation in the 6th amino acid of hemoglobin, valine was inserted instead of glutamic acid.
• One base change causes the cells to be sickled.

Point Mutations

• Two types: transitions and transversions.
• Transitions swap a purine for a purine or a pyrimidine for a pyrimidine. They are more likely to persist to the next generation, causing less disruption to DNA.
• Transversions swap a purine for a pyrimidine. They cause more disruption to DNA and are more likely to be repaired.

Codons

• 3 base pairs create a codon, which determines which amino acid is incorporated.
• A change in the first or second base of a codon is less likely to be tolerated than a change in the third base, due to the wobble effect.

Synonymous and Nonsynonymous Mutations

• Nonsynonymous mutations (replacement substitution) change the amino acid sequence.
• Synonymous mutations (silent mutations) do not change the amino acid sequence, often due to the wobble effect.

Mutation Rate

• DNA polymerase makes 1 error per 100 million base pairs.
• Mutation rate depends on DNA synthesis and repair mechanisms.
• The faster DNA polymerase works, the more mutations accumulate.
• The more mutations in repair mechanisms, the higher the rate of mutations.
• Familial cancers are inherited and associated with double-stranded DNA repairs.

Evolution

• Evolution is a predicted idea that goes against the Law of Thermodynamics

Genome Duplication

• The entire chromosome set (genome) is duplicated.
• This duplication is caused by chromosomes failing to separate during meiosis 1 or sister chromatids failing to separate during meiosis 2.
• Polyploidy : more than 2 sets of chromosomes.
• Gametes have double the number of chromosomes.
• Genome duplication can lead to speciation.
• If a diploid and tetraploid organism mate, the offspring is triploid, which has a low survival rate.
• Many plants are polyploids.
• Angiosperms are one of the most diverse plants due to genome duplication.

Genetic Variation

• We look at the alleles to measure genetic variation.
• Wild type allele: most common allele with the highest fitness.
• Mutant allele: less common and any allele that is different from the wild type.
• Allele frequency: determine the genotype of a large sample of individuals and look at their alleles.

CCR5

• CCR5 is a receptor on the surface of white blood cells, helps fight off viruses, but is mutated in individuals with high resistance to HIV.
• The mutant allele of CCR5 emerged in Europe and led to increased resistance to specific strains of HIV.

Statistical Summaries of Gene Variation

• Mean heterozygosity: fraction of gene loci that are heterozygous in the genotype of the average individual.
• Percentage of polymorphic genes: the fraction of genes in a population that have at least two alleles.

CFTR Receptor

• CFTR receptor is mutated in individuals with cystic fibrosis.
• Lines the GI and respiratory tract.
• When a CFTR receptor mutates, it causes issues with the mucus membranes.
• 500 different mutations cause a mutated CFTR receptor.

Cystic Fibrosis

• Most common mutation studied.
• 4% of the population are carriers for a mutated CFTR gene.
• Mutation occurs on chromosome 7.
• Individuals used to die young, but new treatments have prolonged life.

Hardy-Weinberg Equilibrium -

• P2+2PQ+Q2=1
• Going against Hardy-Weinberg Equilibrium means evolution!
• No mutation, drift, selection, migration, or huge population.

Selection

• Even minimal amounts of selection can cause a change.
• Example: Food spiked with ethanol led to more ADH F (alcohol breakdown).

Kuru

• Kuru is a degenerative brain disease that is caused by a prion, which is a type of misfolded protein.

Malaria

• Placental inflammation due to malaria selection pressure.

Dominant vs Recessive Alleles

• Dominant allele lethal - wiped out in one generation.
• Recessive allele will persist.

Sterilisation Statue

• Attempted to sterilize individuals who were deemed "feebleminded".
• There was a slight allele frequency change over 250 years, but very small.

Mutation is a weak mechanism of evolution -

• Slow effects.
• Creates slightly different alleles, creating very little change in genetic material.

E. CoIi

• Used to study mutations due to fast reproduction rate and no conjugation.
• Accumulated one mutation in populations over 10,000 generations.
• Study of three generations of E. Coli showed that selection helped cause a significant change, while mutation alone did not.

Mutation Selection Balance

• Mutations are created and selection eliminates deleterious mutations.
• The rate at which copies of deleterious alleles are eliminated by selection = the rate at which new copies are created by mutations in allele frequencies and are at equilibrium.

Spinal Muscular Atrophy

• A neurodegenerative disease that causes wasting and weakening of muscles.
• Mutation in the telSMN gene on chromosome 5.
• Second most lethal autosomal recessive disease (after cystic fibrosis).
• It is still prevalent due to mutation selection balance with deleterious mutations.

This quiz explores key concepts of evolution, including how natural selection impacts populations rather than individuals. It discusses examples such as infanticide in lions and the role of gonopodia in fish mating, highlighting the importance of mutations and pre-adaptations. Test your understanding of these fundamental biological principles.