Three out of four children will be tall, since three out of four have a dominant “T” allele for tallness. The recessive “t” allele for shortness is masked whenever it is paired with a dominant “T” allele for tallness. Dominant alleles are shown by a capital letter. Recessive alleles are shown by the lower case of the same letter.

You can visualize this using Punnett Squares, which show the probability of having children who have a certain trait.

3 out of 4 children will be tall:

· 25% chance of being pure tall
· 50% chance of being hybrid tall
· 25% chance of being short

Background notes and definitions:

1. Hereditary traits are determined by specific genes. Within the DNA molecule, genes exist that specify a certain, single characteristic; there is a gene for height, a gene for weight, and a gene for eye color, etc. Variations of the gene relating to the same trait are called alleles.

2. Individuals carry two genes for each trait, one from the mother’s egg and one from the father’s sperm. One of these two genes may be dominant over the other. The dominant allele will mask the other, called the recessive allele. For example, if the father gives a tall allele of the height gene, and the mother gives a short allele, the offspring will be tall. This is because tall is dominant and short is recessive.

3. When an individual reproduces, the two genes split up (segregate) and end up in separate gametes (a gamete is either an egg or a sperm). For example, if the individual is a man, some of his sperm would carry one gene and the some of the same individual’s sperm would carry the other gene.