Human Genetic Variation
What evidence shows modern humans interbred with Neanderthals?
The presence of Neanderthal DNA fragments in modern human genomes, particularly in non-African populations.
What are two examples of traits shaped by natural selection in humans?
Skin pigmentation adapted to UV radiation and lactase persistence in populations practicing dairy farming.
What is the simplest definition of speciation?
The formation of new species due to the cessation of gene flow between populations.
What is the main goal of a GWAS?
To identify genetic variants, such as SNPs, associated with specific traits or diseases.
Why do traits that confer a survival advantage in one environment sometimes become disadvantageous in another?
Selective pressures vary between environments, so traits beneficial in one setting, such as large body size in cold climates, may reduce fitness in others, like warm climates where smaller bodies conserve less heat
Why is the EPAS1 gene associated with Tibetan populations important for survival?
It helps regulate oxygen use at high altitudes, providing an adaptive advantage in low-oxygen environments.
How do visual systems across animals adapt to different environmental needs?
Visual systems evolve specific structures and functions, such as compound eyes for wide-angle vision or camera-type eyes for detailed images, to meet the ecological demands of different species.
How does geographic isolation facilitate speciation?
It prevents gene flow, allowing populations to accumulate genetic differences that lead to reproductive isolation.
How does heritability differ from genetic determinism?
Heritability measures the genetic contribution to trait variation in a specific environment, but it does not mean the trait is entirely controlled by genes.
What evidence shows that traits under selection in natural populations can evolve quickly?
HINT: Finches
Real-time studies, like the rapid change in beak size in finches following environmental changes, show measurable trait shifts within a few generations.
What is the role of admixture in human evolution?
It introduces genetic material from different populations, increasing diversity and enabling adaptations to new environments.
Why is Tiktaalik considered a transitional species?
It bridges the evolutionary gap between aquatic lobe-finned fish and terrestrial tetrapods with features like weight-bearing fins.
What are two examples of prezygotic barriers to reproduction?
Temporal isolation, where species mate at different times, and behavioral isolation, where species differ in mating behaviors.
Why are large sample sizes important for GWAS?
They increase the statistical power to detect small-effect genetic variants associated with complex traits.
How does stabilizing selection affect the genetic diversity of a population?
It reduces genetic diversity by favoring intermediate trait values while selecting against extreme phenotypes, leading to a more uniform population.
How do selective sweeps affect genetic diversity across a genome?
They reduce genetic diversity near advantageous alleles by increasing the frequency of linked SNPs
How does sexual selection contribute to rapid trait evolution?
Traits like elaborate plumage or calls evolve quickly because they enhance reproductive success, even if they impose survival costs.
Why does hybrid sterility often involve chromosomal differences?
Mismatched chromosome numbers or arrangements disrupt meiosis, preventing viable gametes from forming.
What is linkage disequilibrium, and why does it matter in GWAS?
It refers to the non-random association of alleles at nearby loci, which helps locate causal variants but can complicate interpretations.
Why might a polygenic trait, such as body size, evolve differently in response to a sudden environmental shift compared to a gradual one?
Sudden shifts favor individuals with extreme pre-existing traits, leading to rapid selection, while gradual changes allow more genetic recombination and subtle allele frequency shifts, potentially enabling long-term adaptation.
How do patterns of SNP diversity across human populations inform our understanding of migration and adaptation?
They reveal historical migration events, such as the out-of-Africa dispersal, and local adaptations to environments like high altitudes or varying UV levels, shaped by both natural selection and genetic drift.
How does convergent evolution challenge our understanding of shared ancestry?
It shows that similar traits, like mirror-based optics in Spookfish and scallops, can evolve independently in response to similar pressures, not shared ancestry.
How does reinforcement strengthen reproductive isolation between species?
Natural selection favors traits that reduce hybridization, increasing the divergence of prezygotic barriers.
How can GWAS results for the same trait differ between populations?
Different populations may have distinct causal variants, genetic architectures, and linkage disequilibrium patterns that influence trait expression.
How can epistasis and gene-environment interactions complicate predictions about the evolution of complex traits?
Epistasis refers to interactions between genes where the effect of one gene is influenced by the presence of others, while gene-environment interactions occur when the impact of a genetic variant changes depending on environmental conditions. These dynamics combine to produce complex and often unpredictable evolutionary patterns.