MadSci Network: Genetics

Re: Genetic 'Experiments' for 2nd grade students

Area: Genetics
Posted By: Lynn Bry, MadSci Admin
Date: Mon Apr 21 18:45:26 1997
Area of science: Genetics
ID: 861658201.Ge


"Genetics" is probably one of the tougher areas of biology for most students to grasp (yet it's one of the most important..). Thus it's heartening to see that you'd like to tackle the subject with such young children! I think a number of basic concepts can be illustrated in a manner that 2nd graders can understand and appreciate. I'll list a few easy-to-recognize traits. Before you show the kids the traits, I'd consider emphasizing the following points:

  1. Genetic traits are things we can see with our eyes that are the result of having certain gene(s) - hair color, eye color, and the traits listed below.
  2. Each person has thousands upon thousands of genes that contribute to our appearance as well as who we are. Genes are very very small so we can't see them, only the effect they have on us.
  3. We each carry two copies of genes in every cell of our body (except the sperm and egg cells..): one set comes from each parent. For this reason people often say how much we look like our parents, siblings, and relatives. We look alike because we share many common genes.
  4. It also may be useful to mention that as individuals we are the sum of our "genes" and also of our environment (so genes control a lot, but they don't control everything!).
Then take some time to go over some of the characteristics below. I'd make a big table on a piece of paper or the chalkboard so you can keep tabs on how many people in the class have each trait.

I'm guessing most 2nd graders will enjoy anything that lets them stick their tongues out in the name of education, so I'd try the tongue-rolling trait first:

Tongue rolling - stick your tongue out and see if you can roll the edges into a loop. This trait is *thought to be* dominant, meaning you only need one "working" copy of the gene to have it - Tt, or TT. I say "thought to be dominant" as there have been studies suggesting that the trait can be learned. Additionally, identical twins do not always share the tongue rolling trait - a piece of information which indicates that it may not be genetically controlled. I present it, however, as it is a simple test, and because most kids raise no objection to an opportunity to stick out their tongues.

If the students seem to be following along, you may want to work in the fact that the two copies of genes we receive from our parents are not necessarily identical. However, I'd emphasize the nature of observation in determining whether a person has a particular trait.

Hitchiker's thumb - Stick your thumb up, as though "thumbing" a ride. You have the trait if the first part of the thumb bends back more than 45 degrees. This trait is recessive meaning you need two copies of the gene to have it (hh).

Ear lobe attachment - See whether the ear lobes are attached to the side of the head, or whether they hang freely. Unattached earlobes are dominant to attached earlobes.

Widow's peak - People whose hair comes to a point over the middle of their forehead have a widows peak (a dominant trait).

A number of K-12 schools have online projects to collect data concerning genetic traits. Your students can use the WWW to submit their information to some of these projects.

If things can be discussed in more than one session, send the students home with a list of traits to see which ones their parents and siblings have. I'd create a table similar to the one below. When the students return it might be of interest to construct pedigrees of specific traits based on the information each person collected. I don't expect they'll follow all the nuances of inheritance, but it will at least illustrate the concept of where our genetic traits come from.

Person:	Traits:   Tongue rolling     Hitchiker's thumb    Ear lobes    Widow's peak

Making a pedigree:
  1. Generations start with the oldest at the top of the page and the youngest at the bottom of the page.
  2. Squares represent boys, and circles girls.
  3. If a person has the trait, their circle/square is filled in (black). Otherwise it's empty.

In addition, the following sites may of help:

What are some traits in your family
Online Mendelian Inheritance in Man: At the NIH.

Good luck!

- Lynn Bry, MadSci Admin

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