LESSON ONE
ACTIVITY
To predict the offspring of a cross between two individuals using a Punnett Square
PROBLEM
How is chance involved with inheritance of genes?
BACKGROUND INFORMATION
Genes are the plans or instructions that determine what characteristics an individual will have and how that body will run. Pairs of genes for traits are inherited from parents and each parent contributes one gene for each trait to the offspring. These genes provide complicated instructions for determining the body features an of individual.
This exercise will show how genes from each parent can combine. It should be noted that: A. some genes can combine so that their offspring are bound to inherit certain genes and B. some offspring can inherit some genes by chance.
Some features such as eye and hair color are inherited involving only or two genes. If offspring has conflicting genes, such as one gene for blue eyes and one for brown, the body follows instructions in the dominant gene.
MATERIALS
1. 200 cards-100 each with symbols circle and square
2. Container to hold cards
Note: Genes are represented by cards and parent by container. Any pair of cards in container represents gene pair.
PROCEDURE
Draw a box with four squares. Write the genes that the male parent contributes across the top. Write the genes that the female contributes down the left side. Fill in each square with one male gene and one female gene. The filled in chart will demonstrate the predicted genotypes of the offspring.
The Punnett square shows how genes from each parent can combine.
Example 1: Parent has identical pairs of genes and parents are the same
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Both parents have circle-circle gene pairs
So circle will be passed to their offspring
All offspring will have circle-circle pairs
Example 2: One parent has identical pairs and the other parent has the identical pairs of genes but the genes are different from each other.
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Circle circle
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Circle circle
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Square square
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Square square
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One parent has identical pair of genes
So does the other parent—but the 2 parents are different from each other.
Results: All the offspring has the same combination of genes, which is circle-square
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Circle
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Square
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One parent has circle—square pairs
One parent has circle—square pairs
Circle—square are passed to offspring
All offspring has circle—square pairs
Both parents are the same—they each have different pair of genes—circle-square combinations. Each parent can pass on either square or circle genes. The offspring can have 3 different types of genes pairs possible. The types of combinations that can result will follow the mathematical laws of chances.
Note: Mixed pairs of genes will result in the dominant gene dictating the feature that will result.
EXERCISE 4:
1. Get two hundred index cards
2. Draw circles on 100 cards and squares on the other 100 cards
3. Put 100 squares and 100 circle cards in each container
4. Mix well.
5. Draw card from each container and pair them
6. Repeat until all cards are used
7. Chart the results
What proportions were square-square, circle-circle, and square-circle pairs?