Your BFF is a red-headed, left-handed, blue-eyed girl. She finds out that you are taking Human Genetics and wants you to explain to her the genetic basis of her three traits. So, your task is to provide her with the most up-to-date explanation, to the extent that is possible. You have to do so in 400-500 words.

First of all, you should ask your friend if any of her parents also have these characteristics. In this you must explain the concept of heredity, which is the genetic phenomenon that allows us to be able to inherit genetic information from our parents, through DNA. That's because each of us has half the DNA of each of our parents, so we have characteristics in common with them.

After explaining heredity, you should talk about your friend's blue eyes. Blue eyes are characterized by a small amount of melanin, which is the brown pigment that colors our eyes, skin and hair. The more melanin, the darker the eyes. What determines the amount of melanin in the eyes is DNA. If your friend's parents have light eyes, it means they have little melanin and that trait was passed to her through DNA.

Red hair, on the other hand, is the result of a genetic mutation that is passed from parents to children through DNA. People with red hair have a mutation in the gene responsible for the production of melanin. This mutation causes the gene to produce very low levels of melanin for the hair, but it produces large amounts of pheomelanin which is a reddish pigment.

However being left-handed is not related to heredity. Many scientists believe that what determines whether a person is left-handed or not is a set of genes that choose the left or right side of the body as dominant. However, other scientists believe that this is actually linked to a matter of skill and custom.

Red hair, left handed, and blue eyes are recessive traits.

Any trait has its two allele, dominant and recessive. Dominant trait allele if present with the recessive allele, then the phenotype will be of dominant allele.

Suppose A = dominant allele for brown color hair, a = recessive allele for red color hair.

As mentioned above red color hair is recessive in nature. for the recessive traits to show, the alleles should be recessive only.

Aa (brown hair) (parent 1) is crossed with Aa (parent 2) (brown hair). They both have gametes A and a.

Their children will have genotype AA, aa, and Aa. AA = brown color, aa = red color hair, and Aa = brown color hair.

Same case goes with the left hand and blue eyes traits.

So, the girl parents must be having recessive alleles for all the traits, and she must have inherited all the recessive allele only.