Genes are the basic functional units of DNA.
Your DNA contains instructions to build every single molecule in your body. It is the blueprint for you. 
- On the molecular level, humans are 99.9% exactly the same! The difference between you and someone on the other side of the planet is only .01% of your genes.
- To get even stranger, the genetic difference between humans and monkeys is only 99.8%!
- Even stranger… 97.5% of our DNA is exactly the same as that of a mouse! That’s only a 2.5% difference in genetic information. (This is one reason we use mice to test medicines before we test them on humans. Also because mice make lots of babies, fast…)
Humans have about 20,000 functional genes. The other 98% of your genetic material is not used – we call this “junk” DNA.
So how do we inherit genetic traits?
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How Heredity Works:
Each of your parents gives you a copy of their DNA. So you get 2 versions of each gene – one from Mom and one from Dad.
These 2 versions of each gene are called “Alleles”. 
- In a simple case, one version of the gene will be “Dominant”, and the other will be “Recessive”. For example: dark hair is dominant, and light hair is recessive.
- Dominant gene alleles always win over recessive gene alleles.
- If you have one dominant gene (dark hair) and one recessive gene (light hair), then you will express the dominant characteristic – you will have dark hair.
- To express a recessive gene both versions of the gene that you got from each parent must be recessive. So in order to have light hair, both of your parents have to give you the gene for light hair.
So there are 3 basic possibilities:
1. You get 2 dark = you have dark hair
2. You get 1 light and 1 dark = you have dark hair
3. You get 2 light = you have light hair
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The Rules of Heredity:
1. Your parents give you 2 versions of each gene (1 version from each parent)
2. The genes you receive are completely random.
3. The dominant genes will express themselves over the recessive genes.
4. The combinations are endless!
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Want to know what Traits Are Genetic?
Read our original genetics post below!
Hereditary Traits in Humans
What is Genetic ? 