How can a Punnett Square be used to explain basic genetics?

A Punnett Square (Source: Answers in Genesis)

When studying genetics, the Punnett Square is used to simplify the DNA possibilities.  Let’s use the picture to understand skin tones.  The capital letters “A,B” represent a person with more melanin (dark skin), and the lower-case letters “a,b” represent having very little melanin (light skin).  If a dark-skinned mother (A,B) has a child with a dark-skinned father (A,B), their child will have dark skin (A,A,B,B) because that is the only option in the DNA.  If a light-skinned mother (a,b) has a child with a light-skinned father (a,b), then that child will have light skin (a,a,b,b).  If you mix it up with a (A,B) mother and a (a,b) father, you have multiple possibilities.  In fact, some sets of twins have been born where one is light-skinned and the other is dark-skinned. 

Both parents had a “white” mother and a “black” father. Together, they had twins with different skin tones. (Source: Answers in Genesis)

You can see from the chart that there are many possibilities when you mix up mothers and fathers with different skin colors.  The chart shows that the most frequent combination would be a medium-brown skin color (remember that we are all shades of brown).  The majority of the world’s population is also medium-brown.

Here is another example of mixing DNA.  The following example is very basic–the required information needed for specific traits is far more complex, but hopefully this illustration will show the potentials within the DNA combinations.

A basic illustration of the possible combinations in DNA to show variations of the kind (Source: Answers in Genesis)