Background InformationPhysical traits are observable characteristics determined by specific segments of DNA called genes. Multiple genes are grouped together to form chromosomes, which reside in the nucleus of the cell. Every cell (except eggs and sperm) in an individual’s body contains two copies of each gene. This is due to the fact that both mother and father contribute a copy at the time of conception. This original genetic material is copied each time a cell divides so that all cells contain the same DNA. Genes store the information needed for the cell to assemble proteins, which eventually yield specific physical traits.Most genes have two or more variations, called alleles. For example, the gene for hairline shape has two alleles – widow’s peak or straight. An individual may inherit two identical or two different alleles from their parents. When two different alleles are present they interact in specific ways. For the traits included in this activity, the alleles interact in what is called a dominant or a recessive manner. The traits due to dominant alleles are always observed, even when a recessive allele is present. Traits due to recessive alleles are only observed when two recessive alleles are present. For example, the allele for widow’s peak is dominant and the allele for straight hairline is recessive. If an individual inherits: • Two widow’s peak alleles (both dominant), their hairline will have a peak• One widow’s peak allele (dominant) and one straight hairline allele (recessive), they will have a widow’s peak• Two straight hairline alleles (recessive), their hairline will be straight.