Brown Eyed Children

Formal Essay:
Introduction
* Talk about what makes the colour of the eye appear and how it works
Body
* Explain dominant colours * Give examples of how the colours and genes work with different eye colour parents
Finish
* Talk about how eye colours change and what makes them change

Draft essay:
Is there any possible way for two blue-eyed parents to have a green or brown-eyed child?
Eye colour comes from a combination of two black and yellow pigments called melanin in the iris of your eye. If you have no melanin in the front part of your iris, you have blue eyes. An increasing proportion of the yellow melanin, in combination with the black melanin, results in shades of colours between brown and blue, including green and hazel.
The best way to illustrate how this might happen is with an example. Let's say there is a genetic pathway made up of four genes (cleverly named A, B, C, and D) that are needed to make brown eyes. A mutation in both copies of any one of these genes results in blue eyes (these mutations are denoted with lower case letters, a, b, c, and d).
Now let's say that dad has blue eyes because of a mutation in both his copies of gene A and mom because of a mutation in both her copies of gene D. As I am sure you know, we have two copies of each gene, one from our mom and one from our dad. If either parent gives you a brown version of a gene, it will be dominant over the blue copy.
Let's suppose that mom gives you a brown copy of gene A and dad gives you a brown copy of gene D. What colour eyes would you have? Brown.(The same argument works for green eyes as well.)
Another common genetic process that could be responsible for brown eyes from blue-eyed parents is called recombination. When eggs and sperm are made, only one of a pair of chromosomes gets put into an egg or sperm. Before this happens, there is a bunch of DNA swapping that goes on between the pair of chromosomes. Sometimes when the DNA is swapped or recombined, DNA mutations get fixed.
Now imagine that when his sperm is being made, the middle part of the eye colour gene is switched between the two genes resulting in one brown eye gene and one blue eye gene with two mutations. Now dad can produce a brown-eyed child. (Again, the same argument works for a green eye gene as well.)
There are cases, for example, of certain drugs changing a person's eye colour -- the environment clearly has changed what happened to eye colour in this case. Another possibility is that a gene is on or off for some reversible reason instead of an irreversible change in DNA. In this case, something in the environment reverses the change, turning the eye colour gene back on or off.

Final Essay:
Is there any possible way for two blue-eyed parents to have a green or brown-eyed child?
Eye colour comes from a combination of two black and yellow pigments called melanin in the iris of your eye. If you have no melanin in the front part of your iris, you have blue eyes. An increasing proportion of the yellow melanin, in combination with the black melanin, results in shades of colours between brown and blue, including green and hazel.
What we are taught in high school biology is generally true, brown eye genes are dominant over green eye genes which are both dominant over blue eye genes. However, because many genes are required to make each of the yellow and black pigments, there is a way called genetic compensation to get brown or green eyes from blue-eyed parents.
The best way to illustrate how this might happen is with an example. Let's say there is a genetic pathway made up of four genes (cleverly named A, B, C, and D) that are needed to make brown eyes. A mutation in both copies of any one of these genes results in blue eyes (these mutations are denoted with lower case letters, a, b, c, and d).
Now let's say that dad has blue eyes because of a mutation in both his copies of gene A and mom because of a mutation in both her copies of gene D. As I am sure you know, we have two copies of each gene, one from our mom and one from our dad. If either parent gives you a brown version of a gene, it will be dominant over the blue copy.
Let's suppose that mom gives you a brown copy of gene A and dad gives you a brown copy of gene D. What colour eyes would you have? Brown.(The same argument works for green eyes as well.)
Another common genetic process that could be responsible for brown eyes from blue-eyed parents is called recombination. When eggs and sperm are made, only one of a pair of chromosomes gets put into an egg or sperm. Before this happens, there is a bunch of DNA swapping that goes on between the pair of chromosomes. Sometimes when the DNA is swapped or recombined, DNA mutations get fixed.
Again, an example can show how this might work. Imagine dad has blue eyes because of a mutation at the front end of one copy of his eye colour gene and a different mutation at the back end of the other copy of the gene. Each gene has a single mutation but at different places in the gene (see Figure 2).
Now imagine that when his sperm is being made, the middle part of the eye colour gene is switched between the two genes resulting in one brown eye gene and one blue eye gene with two mutations. Now dad can produce a brown-eyed child. (Again, the same argument works for a green eye gene as well.)
Another way to get brown eyes from blue-eyed parents is for something in the environment to affect the eye colour gene. Even though there are well-documented cases in which this happens, the reasons for it are pretty poorly understood.
There are cases, for example, of certain drugs changing a person's eye colour -- the environment clearly has changed what happened to eye colour in this case. Another possibility is that a gene is on or off for some reversible reason instead of an irreversible change in DNA. In this case, something in the environment reverses the change, turning the eye colour gene back on or off.