The following example illustrates how both principles of probability can be comb

Question

The following example illustrates how both principles of probability can be combined to solve problems in genetics. Probability can also be a useful tool in predicting the results of dihybrid and trihybrid matings For example, in mating AaBb x AaBb, one would expect 1/4 of the progeny to be AA, 2/4 Aa, and 1/4 aa, or 3/4 A- to 1/4 aa. Likewise, 1/4 should be BB, 2/4 Bb, and 1/4 bb, or 3/4 B- to 1/4 bb. Now, if the ACa) and BCb) genes are independently assorting, one would expect 34 x 3/4-9/16 of the progeny to be A-B , 1/#x 1/4 to be AAbb, and so forth. Use this ap- proach in answering the following series of questions. If AaBb is mated to AaBb, what is the probability that the offspring will have a. either the phenotype aaB- or the genotype aabb b. either the genotype aabb or the genotype AaBb

Explanation / Answer

Let us construct the punnett square first

a) Probability that the offspring will have either the phenotype -aaB or the genotype aabb:

Now looking into punnett square, we can say probability of phenotype -aaB is 3/16 and probability of aabb is 1/16, therefore applying the rule of addition the answer is 3/16 + 1/16 or 1/4 or 0.25

b) Probability that the offspring will have either the genotype -aabb or the genotype AaBb:

Now looking into punnett square, we can say probability of genotype -aabb is 1/16 and probability of AaBb is 4/16, therefore applying the rule of addition the answer is 1/16 +4/16 = 5/16 or 0.3125

c) Probability that the offspring will have either the genotype A-bb or the genotype AAbb:

Now looking into punnett square, we can say probability of phenotype A-bb is 3/16 and probability of AAbb is 1/16, therefore applying the rule of addition the answer is3/16 + 1/16 or 1/4 or 0.25

d) Probability that the offspring will have either the phenotype A-B- or the genotype aabb:

Now looking into punnett square, we can say probability of phenotype A-B- is 9/16 and probability of aabb is 1/16, therefore applying the rule of addition the answer is 9/16 + 1/16 or 10/16 or 0.625

AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb

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