Why are my eyes brown?

BEDA 2018

Hello and welcome to day 6 of BEDA. So far so good right?

On Fridays I’m going to be talking about genetics, it’s a massive field in the world of biology. Therefore, I’m going to try and break it down and keep things light and simple! My apologies to any geneticists out there!

So I’ll start with a simple question, why are my eyes brown, or hazel or blue?

Well eye colour is an inherited gene.

The leading question to that is whats a gene? and what does inherited mean?

A gene is a chunk of DNA, that DNA works as an instruction manual for the body to make you you! So each gene codes for a different thing and there is a gene specifically for your eye colour. Genes are broken into dominant and recessive genes. The dominant ones are more likely to occur and the recessive ones are less likely to occur.

Inherited means that it comes from your parents.  The sperm and the egg both carry half the amount of genetic material needed to make a human, when they meet the genetic material combines. This means that your genes are inherited from your parents.

So whats the gene for eye colour?

On your 15th chromosome you have two genes located very close together: OCA2 and HERC2. These genes can create the proteins required to make up the eye. 

What makes my eye the colour that it is then?

A person’s eye color results from pigmentation of a structure called the iris, which surrounds the small black hole in the center of the eye (the pupil) and helps control how much light can enter the eye. The color of the iris ranges on a continuum from very light blue to dark brown. The protein produced from the OCA2 gene, known as the P protein, is involved in the maturation of melanosomes, which are cellular structures that produce and store melanin. The P protein therefore plays a crucial role in the amount and quality of melanin that is present in the iris. Several common variations (polymorphisms) in the OCA2 gene reduce the amount of functional P protein that is produced. Less P protein means that less melanin is present in the iris, leading to blue eyes instead of brown in people with a polymorphism in this gene.

What does that have to do with my mother and father?

Each of these two genes comes in two different versions (the dominant and recessive versions we spoke about earlier). The genes come in a brown (dark) and a blue (light) version. Dependent on which your parents have determine which genes are expressed in your eyes. Where brown or dark versions of the gene are more dominant.

Sounds simple!

It is but these two genes have to work together to produce the darker colour, if any of the 2 genes are in the “off position” which is the blue colour then you can end up with lighter eyes. Shown below:

So can you predict a babys eye colour?

Yes you can but there is always an element of chance:

Image result for likelihood of eye color chart

I hope this didn’t get too confusing! Let me know if you have any questions in the comments!

ThatBiologist Everywhere!







The Science of Firework Colours


“Remember, remember, the fifth of November, The Gunpowder Treason and plot”


On this last day of ThatBiologist does Halloween we’re going to explore the science of fireworks! A long time a go I did a 6 facts in 60 seconds post on fireworks here. However today we’re going into more detail on firework colours!

Explosions have been around for a very long time and fireworks have often been used as a sign of celebration. Chinese people are believed to have made explosive rockets in the 6th century CE during the Sung dynasty (960–1279CE). The word “firework” comes from the Greek word pyrotechnics, which means “fire art” or “fire skill”. Fireworks are in essence a controlled explosion inside a missile.

The beautiful colours and styles of fireworks come from a chemical reaction. How it works is that there will be a particular metal compound and an explosion. The metal reacts with the explosion to produce a colour. Sodium compounds give yellow and orange, for example, copper and barium salts give green or blue, and calcium or strontium make red.

Here’s a very cool infographic from Compound Chem explaining that in a bit more detail:

Image result for firework chemical reaction

Make sure you stay safe this guy fawkes night as fireworks are very dangerous. This brings this years ThatBiologist Does Halloween to a close. I hope you’ve enjoyed this week of posts. Feel free to let me know your favourites with a quick tweet or in the comments below!

ThatBiologist Everywhere!




Why aren’t all plants green?


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As part of my time off I took yet another visit to kew gardens with a friend who had never been before. Every time I go I learn a little something different and this time I was wondering about colours of plants. Most plants are green in colour but not all! Today I thought we would explore why this is?

Why are plants green?

Plants are green because their cells contain chloroplasts which have the pigment chlorophyll. This pigment absorbs deep-blue and red light, so that the rest of the sunlight spectrum is being reflected, causing the plant to look green.

What other plant colours can you get?

Think of a colour any colour, you can almost definitely find a plant that colour! Often the colours are found in the flowers but some plants have different coloured leaves too!

Why do plants have different colours?

Often the colours are an adaptation to attract different pollinators. The colours come from different chemicals that absorb different wavelengths of light leaving different colours behind!

Hope you feel like you’ve learnt something a little different this Wednesday! See you on Sunday!

ThatBiologist Everywhere!




6 in 60 – Number 6: Life In Colour


Hello! It’s another 6 scientific things in 60 seconds, three weeks on the trot aren’t you all lucky. Thanks to some inspiration from some pictures of some beautiful corals, this week is all about colour!

  1. Corals glow in an array of colours thanks to a fluorescent light. The light allows you to see the protiens that glow within the coral and the algae.mg22730380.100-4_800
  2. Chameleons rapidly rearrange crystals in their skin to change colour. The crystals reflect different wavelengths of life.1
  3. New evidence suggests that dinosaur eggs were likely a blueish green colour.
  4. Not exactly new news for me but the reason plants are green is due to a pigment called chlorophyll. It is found in high concentrations in the chloroplasts in plant cells.
  5. Not all plants are green! Some plants have almost black coloured leaves, although again this is due to the pigments within the plant.
  6. Men have a higher chance of being colour blind. This is thought to be as males have less rods and cones in their eyes.

That’s all for this week. Remember the 6 in 60 series comes around every Tuesday!

The Sources

Number 1 comes from an article in the new scientist and the beautiful photos have been taken by Oliver Meckles. Number 2 is another article written by Andy Coghlan. Number 3 is again brought to you by an article in the new scientist written by Jeff Hect. Number 4 came from my three years studying biology but nevertheless here is the wiki on chlorophyll for your enjoyment. Number five comes from this article. Number six comes from an article on discoveryeye.org.