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Chapter 21: Problem 13

Assume that a recessive autosomal disorder occurs in 1 of 10,000 individuals (0.0001) in the general population and that in this population about 2 percent (0.02) of the individuals are carriers for the disorder. Estimate the probability of this disorder occurring in the offspring of a marriage between first cousins. Compare this probability to the population at large.

Short Answer

Expert verified
Answer: The probability of the recessive autosomal disorder occurring in the offspring of a marriage between first cousins is 0.0001, which is the same as in the general population (1 in 10,000).

Step by step solution

01

Find the probability that one of the first cousins is a carrier

In the general population, 0.02 or 2% of individuals are carriers. Therefore, the probability that one of the first cousins is a carrier is equal to 0.02.
02

Find the probability that both first cousins are carriers

Since both cousins are part of the general population, we can assume that they have the same probability of being a carrier. To find the probability that both are carriers, we multiply the individual probabilities together: 0.02 * 0.02 = 0.0004.
03

Find the probability that their offspring inherits the disorder

If both parents are carriers, there is a 1 in 4 chance that their offspring will inherit the disorder. In probability terms, this is equal to 0.25 or 25%.
04

Find the probability of the disorder in the offspring of first cousins

To find the probability that an offspring of first cousins will have the disorder, multiply the probability that both parents are carriers (0.0004) by the probability that their offspring inherits the disorder (0.25): 0.0004 * 0.25 = 0.0001.
05

Compare the probability to the general population

The probability of the recessive autosomal disorder occurring in the offspring of a marriage between first cousins is 0.0001, which is the same as the percentage of individuals affected by the disorder in the general population (0.0001 or 1 in 10,000). So the probability of the disorder occurring in the offspring of first cousins is the same as in the general population.

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Most popular questions from this chapter

A form of dwarfism known as Ellis-van Creveld syndrome was first discovered in the late 1930 s, when Richard Ellis and simon van Creveld shared a train compartment on the way to a pediatrics meeting. In the course of conversation, they discovered that they each had a patient with this syndrome. They published a description of the syndrome in \(1940 .\) Individuals with this syndrome have a short-limbed form of dwarfism and often have defects of the lips and teeth, and polydactyly (extra fingers). The largest pedigree for the condition was reported in an Old Order Amish population in eastern Pennsylvania by Victor McKusick and his colleagues \((1964) .\) In that population of \(8000,\) the observed frequency is 2 per \(1000 .\) In all cases, parents of children with the syndrome were unaffected, and all cases can be traced to Samuel King and his wife, who arrived in the area in \(1774 .\) It is known that neither King nor his wife was affected with the disorder. There are no cases of the disorder in other Amish communities, such as those in Ohio or Indiana. (a) From the information provided, derive the most likely mode of inheritance of this disorder. Using the Hardy-Weinberg law, calculate the frequency of the mutant allele in the population and the frequency of heterozygotes, assuming Hardy-Weinberg conditions. (b) What is the most likely explanation for the high frequency of the disorder in the Pennsylvania Amish community and its absence in other Amish communities?

In a population where only the total number of individuals wit the dominant phenotype is known, how can you calculate th percentage of carriers and homozygous recessives?

One of the first Mendelian traits identified in humans was a dominant condition known as brachydactyly. This gene causes an abnormal shortening of the fingers or toes (or both). At the time, some researchers thought that the dominant trait would spread until 75 percent of the population would be affected (because the phenotypic ratio of dominant to recessive is 3: 1 ). Show that the reasoning was incorrect.

List the barriers that prevent interbreeding, and give an example of each.

What are considered significant factors in maintaining the surprisingly high levels of genetic variation in natural populations?
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