# AP Biology Probability & Genetics AP Biology Probability & genetics  Calculating probability of making a specific gamete is just like calculating the.

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AP Biology Probability & Genetics

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

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

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

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 +

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

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

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

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

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

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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