Probability in Genetics

What is Probability?

• Probability is the likelihood that something will happen.

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This does NOT necessarily mean that it WILL happen, it just predicts how often something could/should happen.

• Keep in mind that other factors can affect probability…mutations, chance, crossing over, etc.

Looking at Probability in Coins

• When a coin is flipped, how many possible outcomes (realistically) are there?

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• What is the probability that the coin will land on heads?

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There are two possible outcomes, heads or tails.

Probability would be 1 out of 2 or 50%.

Looking at Probability in Coins

• What would be the probability of flipping four heads in a row?

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There is a ½ (50%) probability EVERY TIME the coin is flipped to get a heads, so for multiple flips you multiply the probabilities together.

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What would this probability be expressed as a percentage?

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½ x ½ x ½ x ½ = 1/16

1/16 = 6.25%

DO NOT FORGET!!!

• Past outcomes DO NOT affect future outcomes.

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Just because you flipped a heads the first time DOES NOT mean you cannot flip heads the second time.

Probability in Genetics

• Probability applies to genetics because the formation of gametes depends on random events…

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An organism has two different alleles for the same gene…so the chances are 1 in 2, or ½, or 50% that one of its gametes carries a particular allele for the gene.

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• Ex: Pp x pp-
• What is the probability the flower will inherit pp?

½ or 50%

Probability in Genetics

• What if you planted 4 seeds from a cross with parents who had genotypes (Pp x Pp)?

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What would be the probability that every seed inherits a pp genotype?

Start with a Punnett Square.

Probability of 1 seed = ¼ or 25%

Probability of 4 seeds = ¼ x ¼ x ¼ x ¼ = 1/256

Probability of 4 seeds = .391%

Application to Genetics?

• Why should people have interest in understanding probability in relation to Genetics/Inheritance?