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Human Genetics 8 th Grade Science. Think About it….  Observe the colors of the kitten in the photo. Look at the kitten’s coat colors and pattern.  Observe.

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Presentation on theme: "Human Genetics 8 th Grade Science. Think About it….  Observe the colors of the kitten in the photo. Look at the kitten’s coat colors and pattern.  Observe."— Presentation transcript:

1 Human Genetics 8 th Grade Science

2 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.

3 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?

4 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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6  (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

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

8 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**

9  javascript:openPDF('view1_sx05_cart078.pdf')

10 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.

11 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.

12 Results

13 Dominant and Recessive Allelles

14  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.

15  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.

16 Probability and Heredity

17 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.

18 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?

19 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.

20 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?

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

22 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.

23 How to Make a Punnett Square

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25 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.

26  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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