The Genetics of White and Gold, Blue and Black: A Holler to 23andMe

The internet is currently losing its collective composure over the perception of colour in the following unremarkable photograph:

Blue and black, or white and gold?

Buzzfeed’s explanation invokes the illusion of compensation; that a single shade can be perceived in multiple ways depending on the lighting context (see image below). There is an excellent write up of the illusion on Jerry Coyne’s blog so I won’t go into any more detail on it here. But you should click through to see a vivid example of the illusion in action.

Compensation illusion: A and B are the same shade.

What I am more interested in is the ratio of “Black and Blue”, to “White and Gold” in that Buzzfeed survey. The sample size is large (>200000 people have voted), and those numbers look suspiciously Mendelian, which got me thinking that perhaps there might be an opportunity to look for a genetic link to colour perception.

Source: Buzzfeed

For those who remember high school genetics, Mendel was the Monk who discovered genetic inheritance by crossing pea flowers of varying colours. When we refer to simple inheritance of traits they are often described as “Mendelian”. At a single locus, perhaps there is a dominant ‘White and Gold’ gene, and a recessive ‘Blue and Black’ gene. At equal frequency in the population, one would expect the phenotypes (white/gold versus blue/black) exactly as shown in the survey. That’s a lot of “ifs”, and highly unlikely, but it is possible that there may be some genetic control underlying this variation in perception.

Mendelian inheritance

Is it possible that compensating in colour perception could be partly influenced by just one locus? It sounds absurd, but if this is not some elaborate trolling then it might actually be a real possibility.

This is where you come in 23andme! As holder of one of the greatest collections of human genetic variation data, I implore you to carry out the white and gold, blue and black survey yourselves. Linked to 600,000 single nucleotide polymorphisms for over 1 million people, we could get a pretty powerful association study done really quickly. The result could tell us something fascinating about the genetics of perception.

Roses reflect greatest above 620 nm, Violets reflect at 420 – 480 nm…

Roses are red,  Violets are blue,  Botany is sexy, But less so than you.

Roses are red,
Violets are blue,
Botany is sexy,
But less so than you.

Along with odour, flower colour is perhaps the most important cue plants use to advertise to pollinators. Change the colour of a flower and that change can have large consequences on which pollinating animals are likely to visit[1]. Bees, for example, are attracted to purple flowers with UV highlights. If that plant were to mutate to white, it could very well find itself being visited by nocturnal moths[2].

In studying plant-pollinator evolution and ecology, it is very important then that we have some objective quantification of the colour of a flower. Human eyes are famously fallible and many insects and birds can see outside the range of our colour vision (400 – 700 nm).

The instrument we use is a spectrometer[3]. It uses optic fibres to bounce an initially white-light beam off the surface you want to measure. The wavelengths of light that are reflected (as opposed to absorbed) determine the colour of the surface you are looking at. The spectrometer collects the reflected light, separates the wavelengths through diffraction and digitises the signal. The result is a graph such as the one above.

In the graph, the wavelength is given on the horizontal axis, while the proportion of reflectance is on the vertical. The rainbow bar above provides an approximation of how the human eye perceives a given wavelength of light. The rose therefore will reflect greatest at wavelengths above 620 nm, the red part of the spectrum. A violet most strongly reflects around 420 – 480 nm. A pure white surface would show high reflectance across the range of the visible light spectrum.

Dedicated to my sweetheart, who for the second year in a row has been alone on Valentine’s.

Kniphofia are red, Agapanthus are blue.

Fieldwork is fun, But I do miss you.