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AP Biology Probability & Genetics

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AP Biology Probability & genetics Calculating probability of making a specific gamete is just like calculating the probability in flipping a coin probability of tossing heads? probability making a B gamete? 50% 100% BB B B Bb B b

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AP Biology Probability & genetics Outcome of 1 toss has no impact on the outcome of the next toss Each toss is independent, just like the distribution of alleles into gametes probability of tossing heads each time? probability making a B gamete each time? 50% Bb B b

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AP Biology Probability & genetics Like a coin toss, each ovum from a heterozygous parent has ½ a change of carrying the dominant allele and ½ chance of carrying the recessive allele The same odds apply to sperm

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AP Biology Calculating probability spermegg 1/2 offspring =x1/4 PPPP PpPpPp 1/2 =x1/4 pppp pP Pp x Pp Pp male / sperm P p female / eggs PPPpPp PpPppp 1/2 =x1/4 1/2 =x 1/4 1/2 +

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AP Biology Chance that 2 or more independent events will occur together probability that 2 coins tossed at the same time will land heads up probability of Pp x Pp pp Rule of multiplication 1/2 x 1/2 = 1/4 PpPp P p

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AP Biology Calculating probability in crosses Use rule of multiplication to predict crosses YyRr x yyrr ?% Yy x Rr x 1/4 1/16 yyrr x

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AP Biology Apply the Rule of Multiplication AABbccDdEEFfAaBbccDdeeFfx AabbccDdEeFF Bb x Bb bb cc x cc cc Dd x Dd Dd EE x ee Ee Ff x Ff FF AA x Aa Aa 1/2 1/4 1 1/2 1 1/4 1/64

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AP Biology Rule of addition Chance that an event can occur 2 or more different ways sum of the separate probabilities probability of Bb x Bb Bb spermeggoffspring 1/2 =x1/4 BbBb 1/2 =x1/4 bBBb 1/4 + 1/2

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AP Biology Rule of addition Example: There are 2 ways that gametes can combine to form a heterozygote The dominant allele could come from sperm and recessive allele from egg (probability = ¼) Or the dominant allele could come from egg and recessive from sperm (probability = ¼) The probability to a heterozygote is ¼ + ¼ = ½

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AP Biology The probability of producing a ppyyRr offspring: The probability of producing pp = 1/2 x 1/2 = 1/4. The probability of producing yy = 1/2 x 1 = 1/2. The probability of producing Rr = 1/2 x 1 = 1/2. Therefore, the probability of all three being present (ppyyRr) in one offspring is 1/4 x 1/2 x 1/2 = 1/16. For ppYyrr: 1/4 x 1/2 x 1/2 = 1/16. For Ppyyrr: 1/2 x 1/2 x 1/2 = 2/16 For PPyyrr: 1/4 x 1/2 x 1/2 = 1/16 For ppyyrr: 1/4 x 1/2 x 1/2 = 1/16 Therefore, the chance of at least two recessive traits is 6/16.

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