WHAT MAKES YOU UNIQUE?

Why are you right-handed or left-handed?

What makes you short or tall?

Inside every cell of your body are chromosomes that carry all of the information about your biological make-up. Eye color, blood type, or body build are characteristics that are determined by distinct units of heredity called genes. Genes are located on chromosomes, and are made-up of complex molecules called DNA. There are thousands of genes on each of our 23 pairs of chromosomes. Inherited characteristics (such as thumb curvature) are traits which are passed on to you by your parents. When you were conceived, you inherited one gene per trait from each parent. A gene may have several forms. Each form is called an allele. Alleles can be dominant or recessive. People with a curved thumb have the dominant trait; they have inherited at least one dominant allele from a parent. A curved thumb (hitch-hiker's thumb) occurs more often in the population than a straight thumb. Traits that appear more often are usually the dominant trait. If you have a curved thumb, you have the phenotype hitch-hiker's thumb. A phenotype is based on how the trait is expressed (i.e.: if it is visible or not visible). To have the dominant phenotype hitch-hiker's thumb, you must have inherited the dominant trait from one or both of your parents. Those who inherited the dominant trait from both of their parents are considered pure dominant genotypes, and those who inherited the dominant trait from only one parent are considered hybrid genotypes. If you have a straight thumb, you are a nonhitch-hiker's thumb phenotype. To have a straight thumb, a person must have inherited the recessive allele from both parents and so is considered a pure recessive genotype.

Alleles are usually represented by capital or lower case letters. Dominant alleles are expressed by capital letters, whereas recessive alleles are expressed by lower case letters. A person who inherited the dominant hitch-hiker's thumb alleles from both parents could be called the genotype HH. A person who does not have a hitch-hiker's thumb could be called the genotype hh. Genotypes that are made-up of two dominant or two recessive alleles are called homozygous. The hybrid genotype which is make-up of one dominant and one recessive allele could be expressed as Hh and is called heterozygous.