Scanning for causes: an introduction to genome-wide association studies

Understanding genetic determinants

You’ve probably been exposed to one news headline or another in the recent past (let’s say the last 5 years) that reads something like “SCIENTISTS DISCOVER GENES THAT CAUSE (X).” X, of course, varies massively based on the study itself (and sometimes the bastardisation of said study by media): it can include describing medical conditions such as cancer, autism or congenital diseases; behavioural traits, such as sexual preferences; or broad physical traits, such as the classic problem of the inheritability of height. Unsurprisingly, you may think that trying to find the genes responsible for some traits should be either a) super easy, or b) super hard, depending on your own philosophical preference or the trait in question. So how do these studies come about, anyway?

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What’s yours is mine: evolution by adaptive introgression

Gene flow and introgression

Genetic variation remains a key component of not only understanding the process and history of evolution, but also for allowing evolution to continue into the future. This is the basis of the concept of ‘evolutionary potential’ – the available variation within a population or species which may enable them to adapt to new environmental stressors as they occur. With the looming threat of contemporary climate change and environmental transformations by humanity, predicting and supporting evolutionary potential across the diversity of life is critical for conserving the stability of our biosphere.

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Islands of speciation and speciation on islands

The concept of a species

We’ve spent some time before discussing the nature of the term ‘species’ and what it means in reality. Of course, answers to questions in biology are always more complicated than we wish they might be, and despite the common nomenclature of the word ‘species’ the underlying definition is convoluted and variable.

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Evolutionary clocks out of sync

Evolutionary time

It shouldn’t come as a surprise to anyone with a basic understanding of evolution that it is a temporal (and also spatial concept). Time is a fundamental aspect of the process of evolution by natural selection, and without it evolution wouldn’t exist. But time is also a fickle thing, and although it remains constant (let’s not delve into that issue here) not all things experience it in the same way.

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Genes in parallel

Adaptation from genetic variation

One of the central themes of this blog, and indeed of evolutionary biology as a whole, is the notion that adaptation is often underpinned by genes. Genetic variation acts as the basis for natural selection to favour or disfavour traits: while this is directly through phenotypic traits (e.g. fur colour, morphology, behaviour), these traits are typically determined by a genetic component. In the early stages of adaptation, evolution can often be observed by changes in the frequency of genetic variants (alleles) within a species or population over time as natural selection acts, gradually leading to the observable (and sometimes dramatic) change in species over time.

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