What are dominant and recessive factors (genes)?
The term gene can be used interchangeably with the words factor, allele or locus. A dominant gene is one that can be expressed if an individual has one or two copies of that gene. For example, the right handed gene is a dominant gene. Therefore, a person may be a righty if they have two righty genes or one righty and one lefty gene. The person with two righty genes is said to be homozygous for right handedness. The person with one righty and one lefty gene, is said to be heterozygous for right handedness. Although this individual has two different genes, the dominant one is expressed and it produces a right handed phenotype. A recessive gene is the weaker gene and can only be expressed in the homozygous condition. A left handed person can only be produced when they inherit two lefty genes. As long as both genes are the recessive lefty gene and there is no right handed dominant gene present, that individual will be a lefty. Remember that sexually reproducing individuals have two copies of each gene, one from each parent. And, in cases where there is a dominant and a recessive gene, the dominant gene will be expressed if the person has at least one copy of that gene. The recessive gene is expressed only if the individual has two copies of that gene.