Exam 3 Flashcards - Evolution

Evolution Exam 3

What are the main problems with ancient DNA?

A: Contamination (from bacteria/fungi or modern humans) and highly degraded DNA (short 100-200bp fragments). Solutions include targeting mitochondrial DNA (more abundant), using Alu-repeat regions to avoid contamination, and working with cold/dry preserved specimens.

Why did PCR revolutionize ancient DNA research?

Before PCR (pre-1985), cloning DNA was slow and labor-intensive. PCR allowed amplification of tiny, degraded fragments from specimens like the Denisovan finger bone (2010).

What conditions favor DNA preservation?

Cold, dry, anoxic environments (permafrost, amber) best preserve DNA> Warm / wet conditions accelerate degredation. I.E. horse dna found in permafrost

What is group selection?

The idea that natural selection can act on whole group, not just individuals

Why is kin selection better than group selection?

Group selection is mathematically flawed, has no clear mechanism, and is rare in nature. Kin selection works due to Hamilton’s rule, genetic evidence and predictive power.

What is the green beard effect?

A rare case where a single gene causes a visible trait, the ability to recognize others with the same trait, and altruistic behavior towards those individuals. I.E. red fire ants killing queens without a specific gene

Define the biological species concept

Species are groups of actually or potentially interbreeding organisms reproductively isolated from other such groups

Define the phylogenetic species concept

The smallest diagnosable cluster with a parental pattern of ancestry or descent

Give examples of pre and post mating isolation

Pre mating: crickets (spring vs fall mating) Post mating: horse + donkey produces sterile mule

Why use DNA to test reproductive isolation?

Genetic markers reveal if populations share alleles or are diverged

Why are species concepts limited?

BSC fails for fossils and asexual species, PSC can split populations arbitrarily

When does PSC fail for Greya moths?

Incomplete lineage sorting, recent divergence causes conflicting gene trees. I.E. Locus 1 groups B +C; Locus 2 groups A+C

Describe allopatric speciation

Physical barrier divides population, stopping gene flow. Subpopulations evolve independently from one another

Evidence for allopatric speciation?

Vicariance (fish and plants seperated by ancient sea level) and founders effects (Greya mitellae from G. piperella subset)

Define vicariance

Geographic seperation of populations by barriers (e.g. mountain rise), leading to independent evolution.

Define founder effect speciation

Small, isolated population diverges rapidly

Compare vicariance vs founder phylogenies

vicariance shows symmetric splits; founder effects show derived species nested within ancestral diversity

Describe disruptive (diversifying) selection

Form of natural selection that favors extreme phenotypes over intermediate forms, potentially leading to speciation

How does sympatric speciation overcome recombination?

Requires strong disruptive selection, assortative mating, and genetic linkage of adaptive and mating traits

What are some examples of sympatric speciation

Apple maggot flies - ongoing divergence on apple vs hawthorn hosts ; Arctic charr in Icelandic lakes - multiple ecotypes in single lakes

How to demonstrate sympatric rather than allopatric speciation?

Must show current sympatry of sister species, no historical geographic barriers, ecological divergence without isolation, and genetic signatures of disruptive selection

Define polyploid

An organism with greater than 2 complete chromosome sets, common in plants like wheat (6n) and potato (4n)

Describe autopolyploid speciation

Speciation via genome duplication within a species. I.E. cultivated potato originated from diploid ancestors through chromosome doubling

Describe allopolyploud speciation

Speciation via hybridization + genome doubling between species. I.E. Bread wheat formed from three ancestral species through sequential polyploidization events

Why are there more polyploid plants than animals?

Plants can self fertilize (establish populations from one individual), reproduce vegetatively (maintain sterile hybrids), tolerate genome duplications better developmentally

What are some exceptions to polyploid animals?

Parthenogenic stick insects and snails

Describe recombinational speciation with an example

fertile hybrid species form without ploidy change via chromosome recombination. I.E. sunflowers originated from hybrids with reshuffled genomes

Define coevolution

Reciprocal evolutionary change between interacting species I.E. host-parasites / plants-pollinators

How does evolution affect medicine and drug resistance?

Germs evolve to survive medicines, the more we use antibiotics, the faster resistance spreads. Some TB strains now survive multiple drugs, and overuse of Cholera antibiotics makes it harder to treat

What is genetic drift?

Random allele frequency changes that are stronger in smaller populations. More impactful in small populations due to sampling error and founder effects / bottleneck

What is a genetic bottleneck?

Sever population reduction lowers diversity I.E. quagga and cheetah

What is the founder effect?

Small colonizing population has non-representative allele frequencies I.E. Greya miellae from G. piperella subset

What are the conditions for the Hardy-Weinberg Equilibrium?

No mutations, no natural selection, random mating, extremely large population size, and no gene flow (migration)

Why is Mayr’s founder mechanism rejected?

He proposed severe bottlenecks drive speciation, but most isolates retain genetic diversity. Modern view emphasizes selection and mild drift

What is parapatric speciation?

Speciation occurs when populations in adjacent but environmentally different habitats diverge due to limited gene flow and varying selection pressues