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11-2 Probability and Punnett Squares
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Genetics and Probability
Genetics is based on probability probability: the likelihood that a particular event will occur the probability of a particular event occurring is divided by all the possible outcomes past outcomes do not affect future ones principles of probability can be used to predict outcomes of genetic crosses
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Probability of getting heads on a coin in one flip is 1 out of 2 or 1/2 or .5 or 50%
What if you want to know the chance of getting two coins to both be tails? You simply multiply each of the coins separate probabilities together ½ x ½ = ¼ Called the Rule of Multiplication
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Probability ranges from 0 to 1
0 = the event will not occur (0 % chance) 1 = the event will occur (100 % chance) There can be fractions in between All the possible outcome probabilities must add up to one
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Probabilities Predict Averages
in order to get the predicted average for a particular event, the event would have to occur many times in a genetics cross, you need many offspring in a generation to come close to the predicted ratio
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Genetic Terminology Punnett squares: a grid used for determining the genetic combinations that would result from a genetic cross These predict the possible outcome percentages of the offspring
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parents gametes
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predicted offspring
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All traits have a 3:1 ratio in F2 generation
Parents Long stems short stems Red flowers white flowers Green pods yellow pods Round seeds wrinkled seeds Yellow seeds green seeds First Generation All long All red All green All round All yellow Second Generation 787 long: 277 short 705 red: 224 white 428 green: 152 yellow 5474 round: 1850 wrinkled 6022 yellow: 2001 green Results All traits have a 3:1 ratio in F2 generation
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