Concept 14.2: Probability laws govern Mendelian inheritance Flashcards
states that to determine this probability, we multiply the probability of one event (one coin coming up heads) by the probability of the other event (the other coin coming up heads).
multiplication rule
By the multiplication rule, then, the probability that both coins will land heads up is .
½X½=¼
With seed shape in pea plants as the heritable character, the genotype of F1 plants is
Rr.
Each egg produced has a ּּ½ chance of carrying the dominant allele (R) and a ּּ½ chance of carrying the
recessive allele (r).
figure 14.9
the probability that any one of two or more mutually exclusive events will occur is calculated by adding their individual probabilities
addition rule
The probability for one possible way of obtaining an F2 heterozygote—the dominant allele from the egg and the recessive allele from the sperm—is .
ּּ¼
The probability for the other possible way—the recessive allele from the egg and the dominant allele from the sperm—is also
ּּ¼
Using the rule of addition, then, we can calculate the probability of an F2 heterozygote as .
ּּ¼+ּּ¼=ּּ½
We can also apply the rules of probability to predict the outcome of crosses involving multiple characters. Recall that each allelic pair segregates independently during
gamete formation (the law of independent assortment)
Thus, a dihybrid or other multicharacter cross is equivalent to two or more independent monohybrid crosses occurring
simultaneously.
For a monohybrid cross of Yy plants, we can use a simple Punnett square to determine that the probabilities of the offspring genotypes are ּּ
¼ for YY, ּּ½ for Yy, and ּּ¼ for yy.
probability of YYRR=
ּּ¼ (probability of YY) X ּּ¼ (RR)= 1/16
Probability of YyRR=
ּּ½ (Yy) x ּּ¼ (RR)= 1/8
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