26:2 Expected Results and Observed Results

• Objectives:

• Discuss the purpose of the Punnett square

• Compare expected results and observed results

• Explain the importance of Gregor Mendel’s work

The Punnett square

• The Punnett square is a way to show which genes can combine when a sperm and egg joins.

• Letters are used in place of genes• A capital letter is used for the dominant

gene• A lower case letter is used for the

recessive gene

• Pure recessive color

Lower case lettersCapital letters are

dominant and the trait will show

Heterozygous colorOne capital letter, one

lower case letter

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Expected Results

• Using the Punnett square you are able to predict traits in offspring.

• The ratio is 1:4 that a dominate trait will show.

Observed Results

• You can not always see the expected results using a Punnett square.

• One parent can have a heterozygous trait while the other parent has a pure recessive trait.

• If that occurs then there is a 50% chance that the trait will show.

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Mendel’s work

• Gregor Mendel was an Australian monk in 1805.

• He notices certain traits in garden pea plants

• Using the scientific method he experimented to find out which traits were recessive and which were dominant in pea plants.

• One trait he noticed was height.

• He observed that when a tall plant was mated with a short plant all of the offspring was always tall.

• He then took the tall offspring and mated them and found that 3/4 of the plants produced were tall and 1/4 were short.

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• Mendel concluded that some traits were present in the tall plants, but were not seen

• His experiments explained the basic law of genetics