Why is incest an issue for some animals?

16 June 2015

Question

Why is incest an issue for some animals and not others?

Answer

Naked Scientists Chris Smith and Georgia Mills considered William's question:

Georgia - Well, to start with, the reason incest is an issue is because of your DNA which is your internal code. So, your DNA is made from both parents. So, half is from your mum, half is from your dad. When these two pieces are put together, so every gene you have - so for example, let's say my eye colour gene, I have one bit from my mum, one bit from my dad. Say, my dad's one is a bit rubbish and codes for a bad eye, but my mum's is good, I still have a good eye. I don't know why I'm using myself as an example here, but then if I breed with someone from my family, they're likely to have the bad gene too. So, when this assortment of genetics happens in the next generation, they're more likely to have two copies of this bad gene. And therefore, exhibit this terrible trait. If you think about it, there's so many genes across throughout your DNA, the chances of this happening are quite high. Another reason why incest is in general a bad idea for animals is because if populations have quite similar DNA, something like a disease can come along and wipe them all out because there's not enough diversity. I was interested in this question, and I did a little research because I had some pet mice and I remember they were meant to be all brothers. One of them was a sister and then suddenly, I had hundreds of mice. I remember thinking that they just didn't care. But apparently, mice do care. They can actually smell whether they're related to each other. But if there's no other opportunities to mate with someone who's not related, they will just take what they can get. So, incest is an issue for pretty much all animals that breed sexually for the reasons I outlined. Most animals do have ways of telling if they're kin or males get trucked out of group. So, it's less likely to happen. But it does happen more often in nature sometimes.

Chris - I suppose it's worth mentioning that if plants don't have sex and exchange genes and by this, I'm thinking of plants like bananas where they're all clones - if you look at where we get our banana plants from, a sucker comes up from the root or you get a cutting, you make a new plant, but it's genetically identical to the parent plant. We've seen with potatoes as well. They're all genetically clones of each other. All it takes is a pathogen or a bug to come in and exploits or finds a loophole in the defences of these particular plant species and it just wipes out the population. We saw this with the Irish potato famine where a fungus evolved the ability to attack a certain strain of potato. And now, the banana is under threat because we've seen the loss of the Gros Michel banana which are very sweet and very nice little banana to Panama disease and now, the Cavendish banana - the big yellow ones we all buy in the supermarket that we're all very fond of - they're under threat too for exactly this reason. So, sex isn't just important to animals. It's important to plants too.

Georgia - Yup! Anything that breeds sexually which does include plants although they might not look like they do.

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