The Gene Machine

By Bill Kendrick
BIO115L, SSU, Spring 1998


This simple program determines some facts about your genes ("genotype") based on physical traits you and your parents show ("phenotype").
(It's based on "Lab 8 - Mendelian Inheritance In Humans" from SSU's Biology 115L lab book.)

People are diploid. That is, they possess two sets of chromosomes. Humans posses several single-gene traits ("phenotypes") where there are only two "alleles" (different forms of the same gene, located in the same place on the DNA strand) for that gene, and the gene behaves in a "dominant" fashion.

P1: O * / F1: O O O O / F2: O O * O
Similar to "yellow peas vs green peas" and "wrinkled peas vs round peas" in the experiments performed by Gregor Mendel (click here to learn more), by looking at the phenotypes of yourself and your parents, I will try to determine your genotype.

The reason I must know about your parents is that when a particular gene has a dominant allele, a person with a genotype with one allele of the dominant gene will have the same phenotype as a person with two copies of the dominant allele. When a person has two identical alleles for that gene, we call the genotype "homozygous". When a person has two different alleles for that gene, we call the genotype "heterozygous". If the homozygous person has the dominant allele, they will have the same phenotype as the heterozygous person. (Take another look at the pea example above). If the homozygous person has tw copies of the non-dominant allele, they show the "recessive" phenotype. This means that, with three possible genotypes (homozygous dominant, heterozygous, and homozygous recessive) we get two possible phenotypes (the dominant one, and the recessive one).

So if you have a dominant phenotype, you could be either heterozygous or homozygous for your genotype. To determine which you are, I will have to consider the possble alleles you might have inherited from your parents. For example, one of your parents might have a widow's peak hairline, but you or your siblings might have a straight hairline (if one of your parents is heterozygous for that trait).

(Punnett square) One way to analyze possible genotypes and phenotypes is using a chart called a Punnett Square. There is one illustrated to the right. The genotypes of the parents are shown on the outside of the grid, and the possible combinations resulting from those alleles are shown on the inside of the square.

Enough! Begin!

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