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Human Genetics 8 th Grade Science

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Think About it…. Observe the colors of the kitten in the photo. Look at the kitten’s coat colors and pattern. Observe the mother cat in the photo. Note her coat color and pattern.

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Who was Gregor Mendal? During this short video consider the following questions: What observation (remember the scientific method!) prompted Mendal to begin studying genetics What do YOU think Mendal’s greatest discovery was?

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Some Important Terms Heredity-The passing of traits from parents to offspring. Genetics- the scientific study of heredity Trait- A characteristic that an organism can pass on to its offspring through its genes.

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(write this) Fertilization- the process in which an egg cell and a sperm cell join to form a new organism. (you don’t have to right all this) In order to conduct his experiments correctly, Mendal had to prevent the pea plants from self pollinating and cross pollinated the plants himself

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Purebred- The offspring of many generations that have the same traits. Mendal began his experiments with pea plants by crossing purebred plants

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The F1 Offspring In one experiment, Mendel crossed purebred tall plants with purebred short plants. Scientists today call these parent plants the parental generation, or P generation. The offspring from this cross are the first filial (fil ee ul) generation, or the F 1 generation. **You do not need to write every word, but you do need to know what the P and F1 generations are**

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The F2 Offspring Once the F1 offspring were full grown, Mendal allowed them to self pollinate and the offspring produce were a mix of both tall and short! About three fourths of the plants were tall, while one fourth were short.

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Experiments With Other Traits Mendel also crossed pea plants with other contrasting traits. In all of Mendel’s crosses, only one form of the trait appeared in the F 1 generation. However, in the F 2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants.

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Results

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Dominant and Recessive Allelles

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Gene- The set of information that controls a trait; a segment of DNA on a chromosome that codes for a specific trait. Alleles- The different forms of a gene. An organism’s traits are controlled by the alleles it inherits from its parents. Some alleles are dominant, while other alleles are recessive.

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Dominant allele- An allele whose trait always shows up in the organism when the allele is present. Recessive allele- An allele that is masked when a dominant allele is present.

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Probability and Heredity

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What Are the Odds? Suppose you were to toss a coin 20 times. Predict how many times the coin would land with heads up and how many times it would land with tails up.

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Test Your Predictions Test your prediction by tossing a coin 20 times. Record the number of times the coin lands with heads up and the number of times it lands with tails up. Combine the data from the entire class. Record the total number of tosses, the number of heads, and the number of tails. Think It Over: Predicting: How did your results in Step 2 compare to your prediction? How can you account for any differences between your results and the class results?

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Probability Probability- A number that describes how likely it is that an event will occur. The laws of probability predict what is likely to occur, not necessarily what will occur.

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Percentage One way you can express a probability is as a percentage. A percentage (%) is a number compared to 100. For example, 50% means 50 out of 100. Suppose that 3 out of 5 tossed coins landed with heads up. Here’s how you can calculate what percent of the coins landed with heads up. Write the comparison as a fraction then, multiply the fraction by 100% to express it as a percentage. Write the comparison as a fraction then, multiply the fraction by 100% to express it as a percentage. Practice Problem Suppose 3 out of 12 coins landed with tails up. How can you express this as a percent?

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Probability and Genetics So how is probability related to genetics? What do you think?

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Punnett Squares A tool that can help you understand how the laws of probability apply to genetics is called a Punnett square Punnett Square- A chart that shows all the possible combinations of alleles that can result from a genetic cross.

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How to Make a Punnett Square

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Coin Crosses Conduct the following activity with a partner: Here’s how you can use coins to model Mendel’s cross between two Tt pea plants. Place a small piece of masking tape on each side of two coins. Write a T (for tall) on one side of each coin and a t (for short) on the other. Toss both coins together 20 times. Record the letter combinations that you obtain from each toss.

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Interpreting Data How many of the offspring would be tall plants? (Hint: What different letter combinations would result in a tall plant?) How many would be short? Convert your results to percentages. Then compare your results to Mendel’s.

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