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Vocabulary: DNA-­‐ DNA is the molecule that holds all of your genetic information. DNA is made up of long strings of nucleotides. The nucleotides come in four different “flavors”: adenine (abbreviated A), thymine (T), guanine (G) and cytosine (C). The order of the G,A,T and C nucleotides in your DNA makes up the instructions, or the “recipes”, that tell the cells of your body how to make all the proteins they need. Proteins determine almost everything about you. You have the color hair you have because of proteins. Your hair is straight or curly because of proteins. Your eye color? You guessed it. Proteins! Genes Each gene is a section of DNA that contains the information for making one type of protein. You have about 20,000 genes in your cells! There may be two or more versions of the same gene. These versions are called alleles. Each allele differs slightly in its DNA sequence, that is, the order of the G, A, T, and C nucleotides. Sometimes these differences in DNA sequence cause differences in the coded proteins, sometimes they do not. If the proteins are different, they may lead to variations in the trait, e.g., curly versus straight hair or freckled versus unfreckled skin. Chromosomes: A cell’s DNA is wound up around proteins (there they are again!) and packaged into chromosomes so that it all will fit in the nucleus. Humans have 23 pairs of chromosomes. One set (of 23) comes from your father, while the other set (of 23) comes from your mother. You have a total of 46 chromosomes. Analogy: Think back to the recipe analogy. Your DNA is composed of letters that form words and the words spell out the recipes for all of your body’s proteins. Each chromosome is a book that holds hundreds to thousands of different recipes. You’ve inherited two copies of each type of chromosome/recipe book-­‐-­‐ one from your mom and one from your dad. Just like your mom and dad may have their own recipe for making spaghetti, some of the genes on their chromosomes will contain different alleles of a gene. Did you know? More than 99.9% of your DNA is found in the nucleus of your cell, but a tiny amount is found in your mitochondria. Humans have ~20,000 genes and 37 come from the mitochondria. Almost every cell in your body has the same DNA. However your skin cells are way different than your muscle cells, which are different than your eye cells. They are different because they have “turned on” a different set of genes. If a gene is turned “off” in a cell, then the protein that gene codes for won’t be made. If a gene is turned “on” in a cell, then the protein will be made! Genotype-­‐ Your genotype is the composition of alleles you have for a particular gene or genes. Remember than many genes come in two or more different “flavors” or alleles—one version (or allele) may code for a protein that gives you freckles (symbolized by a capital F), while another allele may code for an alternate version of that protein that does NOT give you freckles (symbolized by a lower case f). When someone talks about a genotype, they are referring to the alleles you have inherited at a given gene, like the freckles-­‐determining gene. For the freckles-­‐determining gene, you could have one of three possible genotypes: FF or Ff or ff. Phenotype-­‐ the observable characteristics you have based on what your genes say (or genotype). In the case of hair color, your phenotype might be blonde hair, black, red or brown or somewhere in between. For the freckles-­‐determining gene your phenotype is freckled or unfreckled. For each gene, you have 2 copies. (Remember you get one from your mom and one from your dad!) Knowing whether a certain gene is dominant or recessive can help scientists predict whether a person will have a genetic disorder or not. Dominant and recessive traits-­‐ Many genes exist in alternate forms. E.g., there is a gene that determines whether you have freckles or not. One version of a gene codes for freckles and another version of the same gene codes for NO freckles. The freckles version is dominant over the NO freckles version. This means that if you inherit one of each version of the gene, you will have freckles. The freckles trait/gene is dominant over the NO freckles trait/gene. This also means that to have freckle-­‐free skin, you must inherit two copies of the no-­‐freckles version of the gene. That version is recessive to the freckles version. Mutations-­‐ A mistake in the genetic information. Sometimes the mistake is the wrong base pair like an A instead of a G. Other times a base pair is just left out or an extra one is put in the DNA. Whatever the case, if the recipe for your genetic information even has one wrong base pair, that affects the protein that is made. Sometimes no protein will be made at all. Other times a protein is made but it doesn’t work right. Mutagens-­‐ something that causes a genetic mutation. Examples of mutagens are certain chemicals, Ultra Violet Light from the sun, or X-­‐rays. Cake Analogy: You have decided to bake a cake. You’re on your own for dinner tonight so what else were you supposed to make? You aren’t much of a cook but a cake? How hard can that be? All you have to do is add the cake mix, oil, eggs, and water. You dump the cake mix in and the oil, but then your phone dings. Oh ha ha your friends have started a group text and are being ridiculous. You shake your head and laugh. Ok, now for the water. Stir it all up and in the oven it goes. Now to lick the bowl. Yum. Uh oh. You forgot to add the eggs. You don’t realize this at first because the batter still tastes delicious. But when the cake comes out of the oven, it is all crumbly and dry. You see, egg is a binder and adds moisture to the cake. It is an essential ingredient to the recipe of baking a cake. No egg equals a messed up cake. Think back to the analogy of your DNA as a recipe instructing the cells of your body on what proteins to make. What happens if there is a mistake in the recipe? Remember those mistakes are called mutations. So let’s say instead of a G, your DNA says A. How big of a deal can one little wrong base pair be? Think back to your cake. Eggs may not have seemed like that big of a deal, but without them your cake is dry and crumbly. The shape is messed up. Proteins in your body have a unique job based on their shape. Their structure determines what kind of job they have in your cell. If their shape is messed up, they won’t work. Do you see how one little mistake (mutation) can cause a lot of problems in our bodies? Vocabulary Review Activity:
That’s Sketchy
The Rules:
Divide students into two teams. One student from one team comes to the front of
the class, chooses a word from the basket, and draws a picture representation of
the word without writing any letters. Whichever team yells out the correct word
first earns a point. The next student to draw a word comes from the other team,
and so on. Whichever team has the most points when time is called wins. You
may wish to limit each team to two or three guesses per turn.
Materials Needed:
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Each word on a separate small piece of paper
A basket
Chalk or marker
How to Expand the Game:
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This game can be played for a longer period of time to review for
an exam. You can also include bonus words from other units for
deeper review.
Look Out For:
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Make sure to have a set time period so that students feel it is fair
for one team to win.
Thanks to our friends at Flocabulary: Vocabulary Minigames https://www.flocabulary.com/vocabulary-­‐mini-­‐games/