All living organisms contain DNA filled with genetic information. Humans are no different! In each of your body cells you have 23 pairs of chromosomes, a set inherited from each parent. This combination of genetic information leads to similarities and differences found in bloodlines and leads to genetic diversity.
There are several easily identifiable traits (listed below) with known inheritance patterns. An expressed trait (what you can see) is called a phenotype. The phenotype is determined by the genes present. The genes that make up the phenotype are called the genotype. The genotype is made up of alleles. An allele is a variation of a gene (one from mom, one from dad) and are categorized as being dominant or recessive.
A dominant trait is designated by a capital letter allele and a recessive trait is designated by a lower-case letter allele. A heterozygous genotype is one capital allele and one lower-case allele (Gg) and displays the phenotype of G because the dominant allele masks the recessive allele. A homozygous dominant genotype would be two dominant alleles (GG) and display phenotype G. A homozygous recessive genotype would be two lower-case alleles (gg) and display a phenotype of gg.
Here are some examples of common single-trait dominant and recessive phenotypes and their genotypes.
• Free earlobes, not attached to the head, is a dominant trait. Genotype is EE or Ee
o Attached earlobes is a recessive trait. Genotype is ee
• Widow’s peak hairline is a dominant trait. Genotype is WW or Ww
o Straight hairline is a recessive trait. Genotype is ww
• Chin dimple is a dominant trait. Genotype is DD or Dd
o No chin dimple is dd
• Interlocking fingers (clasp your hands as through you are ready to pray and look at your thumbs). Left thumb over right thumb is a dominant trait. Genotype is FF or Ff
o Right thumb over left is recessive. Genotype is ff
• Tongue rolling. If you can make a “U” with your tongue, it is a dominant trait. Genotype is TT or Tt
o If you can’t do it, it is a recessive trait tt
Look at yourself, or a family member, or a friend or even your favorite celebrity, and identify a phenotype from the list above. Then, discuss the following points:
• What phenotype are you observing?
• What conclusions can you make about the person’s genotype and/or their parents’ genotype?
• What predictions can you make about their offspring?
