Watch this YouTube video about DNA: http://www.youtube.com/watch?v=qy8dk5iS1f0
Look at your reflection in the mirror. Why do you have blonde, brown,black, or red hair? (Or any color in between- and don't tell me it's from a bottle!) Why are your eyes blue, brown, gray, hazel, green, etc.? Why is your face shaped as it is; your eyes the shape and size they are?
It is because your genotype (Your genes- not your jeans- are made up of DNA, and those genes come together to make up your genotype) determines your phenotype (how you look). So everything can be traced back to your DNA.
Have you ever heard of polydactyly? This is when people (or dogs or cats) have extra fingers and/or toes! There are many examples, like the six-fingered man (the count) in The Princess Bride. While that is a fictional reference, it does occur in reality as well. It happens when there is a mutation in the way DNA gets copied...
So, how do you determine your DNA? When you become a developing embryo, your cells are constantly dividing and multiplying, through cell division. You received one set of DNA from each parent cell, and it mixes from there. Each time there is a division of cells, there is the potential for mutation, although our bodies have certain ways to "proofread" the results before cementing it into our genotype.
Remember: skim chapter 11, and get ready to talk about DNA!!
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