Do you have your father’s nose? Your mother’s chin? Does your cousin look a lot like you? Our genes are what determine our physical characteristics. Genes decide the color of our hair, the size of our feet, the shape of our eyes, and many other things. Our parents pass on these genes to us.
Many of our physical characteristics are determined by the interaction of many genes. However, only one gene is needed in order to pass on some traits – in other words, if you have a specific gene, you will exhibit that characteristic.
You get two genes for every trait – one from your mother and one from your father. Some genes are dominant (represented with capital letters), which means you only need one of them to exhibit that characteristic. If you don’t have any dominant genes for a characteristic, you are considered recessive (represented with small letters) for that trait. Scientists often call these letter combinations genotypes, while the characteristics they represent are known as phenotypes.
Genetic Physical Traits
The following are physical traits that are determined by one gene:
If your earlobes hang free at the bottom, you are dominant for that trait. This means you only need one dominant gene for this characteristic, and you are either EE or Ee. If your earlobes are attached, you are recessive for that trait. This means neither of your parents passed the dominant gene to you. In this case, you are ee.
If you are able to roll your tongue into a U shape, you are dominant for that trait. This means you only need one dominant gene for this characteristic, and you are either TT or Tt. If you cannot roll your tongue, you are recessive for that trait. In this case, you are tt.
If you have dimples (even one!) when you smile, you are dominant for that trait. This means you only need one dominant gene for this characteristic, and you are either DD or Dd. If you don’t have dimples, you are recessive for that trait. In this case, you are dd.
Geneticists use many tools to help predict traits of offspring. One of the tools is called a Punnett Square, a grid in which the frequencies of different phenotypes can be determined by crossing two particular parents. For example, if both parents have genotypes of Dd, the chances of their children having dimples can be illustrated like the diagram below.
In this case, even though both of these parents have dimples (Dd), they actually have a one in four (25%) chance of producing a child without dimples (dd). Three in four children will carry the dominant trait, and will therefore exhibit dimples.
Students love to complete these activities, and you can design lessons as basic or as complicated as the ages and abilities of your class. For some great worksheets and activities involving genetics and Punnett Squares, check out the following lessons.
Additional Genetics and Punnett Square lessons
Pupils work on exercises involving genotypes, phenotypes, dominant genes, and recessive genes. They also work on using Punnett Squares to work out genetic questions. The problems increase in difficulty.
This is an interesting activity that asks learners to conduct a simulation involving a monster with one or two horns.
Here is a lesson that involves a class survey to identify physical traits. Scholars find out which of their classmates have dimples, hitchhiker’s thumb, etc. They can then graph their findings.
Learners examine pea pods and discuss the differences within a group. They then talk about how dominant and recessive traits, genotypes, and phenotypes help produce variation in a population.