IGA 8/e Chapter 2

22 Chapter Two8. What statistical rules might be relevant, and in what situations can they beapplied? Do such situations exist in this problem?Answer: The major statistical rule needed to solve the problem is theproduct rule (the “and” rule). It is used to calculate the cumulativeprobabilities described in part 2 of this unpacked solution (e.g., What isthe probability that Martha’s parent inherited the galactosemia allele ANDpassed that allele onto Martha AND Martha will pass that allele on to herchild?).9. What are two generalities about autosomal recessive diseases in humanpopulations?Answer: Autosomal recessive disorders are assumed to be rare and tooccur equally frequently in males and females. They are also assumed tobe expressed if the person is homozygous for the recessive genotype.10. What is the relevance of the rareness of the phenotype under study inpedigree analysis generally, and what can be inferred in this problem?Answer: Rareness leads to the assumption that people who marry into afamily that is being studied do not carry the allele, which was assumed inentry (6) above.11. In this family, whose genotypes are certain and whose are uncertain?Answer: The only certain genotypes in the pedigree are John’s parents,John’s brother, and Martha’s great-grandmother and grandmother. Allother individuals have uncertain genotypes.12. In what way is John’s side of the pedigree different from Martha’s side?How does this difference affect your calculations?Answer: John’s family can be treated simply as a heterozygous-byheterozygouscross, with John having a 2 / 3 probability of being a carrier,while it is unknown if either of Martha’s parents carry the allele.Therefore Martha’s chance of being a carrier must be calculated as a seriesof probabilities.13. Is there any irrelevant information in the problem as stated?