I think people generally pick 30 - 100 million different distinct "genes" are in the human chromosome. This might code for a billion or more different "traits". Amazing, isn't it?

A lot of people would like to know the answer to that question.The Human Genome Project human-gen-proj is a group of people trying to map every one of our estimated 80,000 genes. Unfortunately, that still won't answer your question. Genes are basically recipes for making us (or oak trees, or earthworms). If each gene acted like a recipe for making one dish in a meal, we would be able to answer your question as soon as we had the genes mapped. 8 recipes would make 8 dishes, right? So do 80,000 genes make 80,000 traits? Nope.

The 'gene cookbook' works more like this: You have to read 10 different recipes at once to make a salad. When you add pepper to a sauce, garlic is added to your biscuits, your lemonade turns blue, and your lasagne freezes. When you set the oven for your cake, your carrots disappear. If you follow a recipe on a cloudy day you get ice cream, on a sunny day the same recipe makes mashed potatoes. That's more like the way genes create us.

Here's why:

1. "Additive effects", meaning that many genes may work together to produce a single trait. For example, your height is determined by many different genes, but the final trait can be expressed as one number (though it will change over time). If many genes are working together, and you might have any combination of those genes. What will the *population* look like? (hint: compare this with a simple dominant trait. For example, let's say that if you have one P gene your ears will be pointy. What will a population look like if both P and p are equally numerous? Compare this with a population where many genes control ear shape.) (Many genes can = 1 trait.)

2. "Pleitropy" (PLEE-oh-troh-pee), meaning one gene can affect many things which don't even seem to be related to each other. What would happen if your body had genes that were an *incorrect* recipe for insulin? If we couldn't treat you for this disease, effects would be found from your eyes to your feet. What do we call this disease? (1 gene can = many traits.)

3. "Epistasis" (eh-PISS-tih-sis), which basically mean that one set of genes interferes with another set so we don't see the trait they'd normally cause. For example, Labrador retrievers have one set of genes that produce the black pigment for the fur, skin, and eyes. Another set determines whether the pigment will actually be put into the fur. So just because a dog can make the pigment doesn't mean the trait will be *expressed* by the dog. Does a yellow lab have the genes for black pigment even though it's yellow? Could you tell by looking at it? (Hint: read this paragraph carefully, there's a clue in it.) (A few genes can = 1 trait or a few traits)

4. The effects of environment, which may change the way genes are expressed. For example, what happens if your genes code for you to be tall, but you don't get good nutrition when you're growing? (1 gene or a few genes can = one trait, but whether the trait shows up depends the environment.)

So, 80,000 genes = how many traits? Beats me, but it's an interesting question.

This is a great question! First, I would like to know what the students think about "traits that are specified by the genes on the chromosomes" versus "traits that are determined by the environment." For example, do you think that eye color is determined by your genes? Why or why not? How about your sense of humor? Would that "trait" be something that is determined by the DNA in your cells? This is a big debate among many scientists. We really do not know how many traits are "encoded" by our genes and we certainly do not understand fully how the environment influences those traits that are a part of our genetic makeup.
Along a different line, we do know that many genes are necessary to carry out the basic functions that our cells need to survive. When one of these "traits" or genes is "mutated" (abnormal), then a disease can result. Scientists are discovering more and more of these genes every day. You may have heard about something called the "Human Genome Project." This is a big, international project involving many scientists--the goal is to try and determine all of the genes on the 23 pairs of chromosomes. Even if this is accomplished, we still won't know for sure what each gene does; that will be the next phase of the project. The best guess right now is that there about 100,000 different genes spread among the 23 chromosomes. So there is lots to discover!

This is a tough question, and I bet a lot of scientists would like to know the answer. The problem is that the genes on our chromosomes provide the instructions for virtually everything that goes on in our bodies. Our chromosomes contain information for all the traits you can think of and then some. Everything from hair color to the shape of enzymes in your liver: millions and millions of different things which are needed to make person.