Last week, we started talking about genetics and earlobes. This time, we will continue exploring dominant and recessive traits.

IMPORTANT! As I said last week, if your results cause you to think that you are adopted, don't panic. Scientists are learning new things about genetics every day, and the more we learn; the more complex it gets. We THINK that these traits are controlled by a single gene, but future studies may change that.

We looked at inheritance of earlobes, and saw that free earlobes is a dominant trait, and attached earlobes is a recessive trait. Now we will explore and easier way to look at how these traits are inherited, using something called a Punnett square.

To make a Punnett square, start by drawing a Tic-Tac-Toe board.

| |
_____|_____|_____
| |
| |
_____|_____|_____
| |
| |

In the left hand column, we will put the possible genes that an offspring could get from its father. We will stick with the same symbols that we used last week, with "E" for free lobes and "e" for attached lobes. If your father has attached earlobes, which is recessive, then he has two recessive genes (ee), so you would put an "e" in both of those boxes. If your father has free earlobes, then it could either he might have two "E"s or he might have one of each, "Ee". To find out which could take some research on his parents, and possibly their parents, etc. For now, lets say that he has one of each, "Ee". We put an "E" in the middle box on the left side, and an "e" in the bottom box on the left side.

| |
_____|_____|_____
| |
E | |
_____|_____|_____
| |
e | |

Then, across the top, we will put the possible genes that an offspring could get from its mother. For this example, we will let the mother also have "Ee", which means that while she has free earlobes, she also carries the recessive gene for attached lobes. We put her genes across the top.

| E | e
_____|_____|_____
| |
E | |
_____|_____|_____
| |
e | |

Now comes the important part for the science of genetics. We fill in the other blocks by combining the letter at the top of the column, and the letter at the left of the row. For the center box, the letter at the top is an "E", and the letter at the left is an "E", so in that box, we would write "EE".

| E | e
_____|_____|_____
| |
E | EE |
_____|_____|_____
| |
e | |

Then we do the same thing for the other boxes.

| E | e
_____|_____|_____
| |
E | EE | Ee
_____|_____|_____
| |
e | Ee | ee

This shows us the four possible combinations that each offspring could have.

There is one box with "EE", so there is a 25% chance (one in four) that each offspring will get "EE", which means two dominant genes. That child will have free earlobes.

There are two boxes with "Ee" which means that there is a 50% chance (two 25%s combined) that the child will get "Ee", one dominant gene and one recessive gene. That child will have free earlobes, but will carry the gene for attached earlobes, just like her parents.

There is also one box with "ee", so there is a 25% chance that the offspring will get "ee". That child will have attached earlobes, even though his parents both have free earlobes.

Once you get a grasp on that idea, try some other combinations. What if the father had "ee" and the mother had "EE"? What if the father had "ee" and the mother had "Ee"?

Now, don't confuse % chance with actual percentages. In the example with the boxes above, there was only a 25% chance of the child having attached earlobes, "ee". If the parents had four children, they might all have attached earlobes, or they might all have free earlobes.

Think of it like flipping a coin. When you flip the coin, there is a 50/50 chance of getting heads or tails. Now, what if you flipped the coin five times and each time it came up heads. What is the chance that your next flip will be heads? 50%. Each flip has a 50% chance of being heads. The same is true of genetics. If there is a 25% chance that offspring will have attached lobes that does not mean that if there are four children, only one can have attached lobes. It means that each has a 25% chance of having them.

There are several other traits that seem to be controlled by a single gene, and you can make Punnett squares for them too. Some that you might try include:

Hairline: Having a "widow's peak" is dominant, and a straight hairline is recessive.
Dimples: Having dimples is dominant.
Hitchhiker's thumb: Open your hand as wide as you can. If your thumb bends backwards that is hitchhiker's thumb, which is recessive. Straight thumbs are dominant.
Cleft chin: Having a cleft chin is dominant.

One last thought on the subject. Remember that we are constantly learning more and more about genetics. Each of these may be found to be controlled by more than one gene, so don't panic if the results don't match reality. As long as you have the "I love ice cream" gene, everything will be OK.

Have a wonder-filled week.

This week's experiment is a result of me looking over the various state science standards to see where I have gaps in coverage. One big gap turned up in genetics, so I began working on a couple of genetics videos. I kept finding more and more interesting stuff, and could not wait to share some and let you in on the fun. This time, we will take a quick look at dominant and recessive traits, to see what that really means. To explore that, you will need:

- your ears
- the ears of other family members

Friends, Romans, and countrymen. Lend me your ears! I only need them for a moment, just long enough to look at your ear lobes. No, it does not matter if they are pierced or not. We just want to see how they connect to your head.

For some people, the ear lobes are connected directly to the side of their head, all the way to the bottom of the lobe. We will refer to those as attached ear lobes. I have attached ear lobes.

For other people, the ear lobe hangs down beyond the point of attachment. We will refer to those as free ear lobes.

OK, so why do some people have attached lobes and others have free lobes? That is where the science of genetics comes in, because ear lobe attachment is an inherited trait. That's right. You got your ear lobes from your parents.

Inside most of the cells in your body (not red blood cells) there is a complete set of instructions for your body and how it develops. These instructions are chemicals that fit together into very long molecules called DNA. In a human cell, the DNA forms 46 strands, called chromosomes, which fit together to form 23 pairs. Each pair of chromosomes fits together, sort of like the teeth in a zipper. Arranged along the chromosomes are sequences of chemicals that form genes. Each gene is a part of the chromosome that some of the instructions for making you you. Genes control the color of your hair, how tall you will be, the color of your eyes, the color of your skin, and many, many other characteristics, called traits.

Now, it gets even better. Some genes control more than one trait, and some traits are controlled by several genes working together. Some genes turn other genes on or off. Some genes don't do anything that we can detect so far. That does not mean that they are useless, just that we don't yet know what they do.

The connection of ear lobes seems to be controlled by a single gene. I say "seems to be" because there is still a tremendous amount that we don't know about genes. For example, many books list tongue rolling (the ability to roll up the sides of your tongue to form a tube) as a single gene trait, but recent studies suggest that it is not.

So that must mean that you can look at your ears and tell whether you got the gene for your ear lobes from your father or your mother, right? No. Actually, you got an ear lobe gene from each of them. Remember that I said your chromosomes form pairs that are zipped together. One strand of each chromosome pair is from your father, and the other strand is from your mother. So, what happens if your father has attached ear lobes and your mother has free ear lobes? Do you wind up with ears that don't match, one attached and one free?

No. Some genes are dominant, and others are recessive. Dominant genes take priority. In the case of ear lobes, free lobes are dominant and attached lobes are recessive. Since you got one gene from each parent, and there are two options for each gene; there are four possible combinations.

1. If you got a dominant, free lobe gene (we will label that E) from your father and a dominant, free lobe gene from your mother (E), then you have (EE), two dominant, free lobe genes, so your ears will have free lobes.

2. If you got a recessive, attached lobe gene from your father (we will label that with a lower case e) and a dominant, free lobe gene from your mother (E), then you have (Ee), one dominant, free lobe gene and one recessive, attached lobe gene. The dominant gene takes priority, so your ears will have free lobes.

3. If you got a dominant, free lobe gene from your father (E) and a recessive, attached lobe gene from your mother (e), then you have (eE), one dominant, free lobe gene and one recessive, attached lobe gene. The dominant gene takes priority, so, again, your ears will have free lobes.

4. If you got a recessive, attached lobe gene from your father (e) and a recessive, attached lobe gene from your mother (e), then you have (ee), two recessive, attached lobe genes, so your ears will have attached lobes.

Now, if you are reading this and realizing that you have attached lobes and both of your parents have free lobes, don't start worrying that you are adopted. Remember that each of your parents also has a pair of genes that control ear lobe attachment, and that you only get one from each parent. If your father has (Ee), then you have a 50/50 chance of getting either an E (dominant, free lobe) or an e (recessive, attached lobe) gene. The same is true for your mother, so if both are (Ee), they would both have free lobes, but there is a one in four chance that you could wind up with (ee), getting the recessive attached lobe gene from both parents.

When you add in more variables, it gets more difficult to predict the outcome. For example, hair color depends on the interaction of several genes that control different amounts of different pigments, and it is also genetically connected to skin tone and eye color. That is why it is much easier to deal with traits that are controlled by a single gene, such as ear lobe attachment.

Next time, we will look at some other traits and learn a bit more about the wonders of genetics.

Have a wonder-filled week.

This week's experiment comes from tonight's supper. I have been craving a big pot of Great Northern Beans; so last night I put some into a pot of water to soak overnight. The results reminded me of a fun science experiment. To try it, you will need:

- a package of dry beans (any kind will do)
- a drinking glass
- water
-a metal cookie sheet or cake pan

Fill the glass full of dry beans. Add enough water to fill it to the top, and place the glass in the center of the metal pan. Put it somewhere nearby, where it won't be in the way, and then go about your daily routine. After a few hours, you will hear a clink as one of the beans falls out of the glass onto the pan. Then you will hear another. Over the next few hours, you will continue to hear the sounds of the beans falling, so unless you are a heavy sleeper, don't try this at night. (And of course you would never hide your experiment in your sister's closet before bedtime!) You will find that the beans expand to more than twice their original size.

Why does that happen? The dry beans absorb the water to start the process of sprouting. The water softens the cells, and is absorbed into them by the process of osmosis. This causes the cells to expand, making the beans larger.

When your experiment is finished, put the beans into some water with some spices of your choice. Then bake some corn bread, and you are ready for a tasty treat.

Have a wonder-filled week.

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