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home / study / science / biology / biology questions and answers / If 1 Percent Of Individuals In A Population At Hardy-Weinberg Equilibrium Express A Recessive ... Question: If 1 percent of individuals in a population at Hardy-Weinberg equilibrium express a recessive tra... Edit question If 1 percent of individuals in a population at Hardy-Weinberg equilibrium express a recessive trait, we might like to know what is the probability that the offspring of any two individuals who do not express the trait will express it. This asks you to use the probability thinking from both population genetics (where expectations come from HWE) and Mendelian genetic crosses (where expectations are made about the outcomes of a specific mating).

The logic: We know that two carriers (individuals not expressing the trait, but being able to pass the recessive alleles to offpsring) have a 25% chance of producing a child that inherits recessive alleles from both parents (1/2 x 1/2 = 0.25). But, now we need to know how likely it is that individuals in the population are carriers, so that we can predict the probability that any two people not expressing the trait will have a child that does express the trait.

To estimate this from the information that we know -- 1% of individuals express the recessive trait -- we need to recognize what this frequency represents. Let the frequency of the rare recessive allele be represented by 'q'.

c) Carriers are heterozygotes, so we can estimate their frequency in the population using the HWE expectation of 2pq. Using this equation, what is the frequency of carriers of the recessive allele in the population? ____________

d) What is the probability that the offspring of two individuals who themselves do not express the disease will express it? Here we need to first calculate the probability that two individuals who are carriers mate, which is the product of the probabilities of each being a carrier. And then we need to multiply that by the probability that two heterozygotes have an offspring that inherits two copies of the recessive allele. Enter that combined probability here: ____________

** Note: Some of you may have realized that, to be precise, we should incorporate the information that the two individuals do not express the disease, meaning that we should only be considering the 99% of individuals that do not express the trait when we do this calculation. This ends up modifying the probability only slightly and both answers are scored correct.

Enter numeric answers to 4 decimal places, if rounding is necessary (e.g., 0.66666… should be entered as 0.6667).

Answer 1