Problem 1 A curious polymorphism in human populations has to do with the ability to curl up the sides of the tongue make a trough (“tongue rolling”). Some people can do this trick, and others simply cannot. Hence it is and example of a dimorphism. Its significance is a complete mystery. In one family, a boy was unable to roll his tongue, but, to his great chagrin, his sister could. Furthermore, both his parents were rollers, and so were both grandfathers, one paternal uncle, and one paternal aunt. One paternal aunt, one paternal uncle, and one maternal uncle could not. A. Draw the pedigree for this family, defining your symbols clearly, and deduce the genotypes of as many individual members as possible. B. The pedigree that you drew is typical of what type of mode of inheritance C. If the boys parents had a sister what is the probability that she would be able to roll her tongue. D. In a study 33 pairs of identical twins, both members of 18 pairs could roll, neither member of 8 pairs could roll, and one of the twins in 7 pairs could roll but the other could not. Because identical twins are derived from the splitting of one fertilized egg into two embryos, the members of a pair must be genetically identical. How can the existence of the seven discordant pairs be reconciled with your genetic explanation of the pedigree?

Answer Problem 1 Draw the pedigree for this family, defining your symbols clearly, and deduce the genotypes of as many individual members as possible R/r R/r -/r ? ? If R is roller and r is no roller -/r r/r R/r R/r R/- R/- r/r r/r r/r R/- Sister could roll parents were rollers, and so were both grandfathers, one paternal uncle, and one paternal aunt One paternal aunt, one paternal uncle, and one maternal uncle could not The pedigree that you drew is typical of the autosomal dominant mode of inheritance. It is present in both parents and offspring. It is also present in both females and males

Answer Problem 1 R r R R/R R/r r R/r r/r C. If the boys parents had a sister what is the probability that she would be able to roll her tongue. There is 75% chance she would be able to roll her tongue. R r R R/R R/r r R/r r/r How can the existence of the seven discordant pairs be reconciled with your genetic explanation of the pedigree? Two possible answers there could be an environmental element affecting the phenotype expression or the R allele might not be fully penetrant

Problem 2 Duchenne’s muscular dystrophy is sex linked and usually affects only males. Victims of the disease become progressively weaker, starting early in life. A. What is the probability that a woman whose brother has Duchenne’s disease will have an affected child? B. If your mother’s brother (uncle) had Duchenne’s disease, what is the probability that you have received the allele? C. If your father’s brother had the disease, what is the probability that you have received the allele?

Answer Problem 2 A possible pedigree D/d D/Y D/- d/Y D/Y 1/8 A. What is the probability that a woman whose brother has Duchenne’s disease will have an affected child? A possible pedigree D/d D/Y D/- 1/2 The probability of passing it on to the child is 1/2 Because Duchenne’s disease is X-linked we know it can only be inherited from females. Therefore the maternal grandmother must be a carrier. d/Y D/Y 1/8 Probably the child is male is ½ and the chance of passing the allele is ½. Therefore the chance of having an affected child is ½*1/2*1/2=1/8

Answer Problem 2 Same pedigree applies D/d D/Y D/- d/Y D/Y ½*1/2=1/4 If your mother’s brother (uncle) had Duchenne’s disease, what is the probability that you have received the allele? Same pedigree applies The probability of passing it on to the child is 1/2 D/d D/Y D/- 1/2 Because Duchenne’s disease is X-linked we know it can only be inherited from females. Therefore the maternal grandmother must be a carrier. d/Y D/Y ½ is the probability she passes it to you ½*1/2=1/4

Answer Problem 2 A possible pedigree applies D/d D/Y d/Y D/D D/Y 0% C. If your father’s brother had the disease, what is the probability that you have received the allele? A possible pedigree applies D/d D/Y d/Y D/D D/Y 0% Because the disease is rare it is a good assumption that your mother does not have the disease allele. Therefore because the disease can not be inherited through a male, your chance of getting the disease is zero or the rate of a new mutation

Problem 3 Here are two human pedigrees. The black symbols represent an abnormal phenotype inherited in a simple Mendelian manner. A. For each pedigree, state whether the abnormal condition is dominant or recessive. Try to state the logic behind your answer. B. For each pedigree, describe the genotypes of as many persons as possible.

Answer Problem 3 A. For each pedigree, state the most like mode of inheritance. Try to state the logic behind your answer. Most likely X-linked dominant. Occurs in every generation. All males are affected. Appear to pass only through females Most likely autosomal recessive. Occurs following the mating of two related individuals and skips a generation

Answer Problem 3 Most be X/x because of x/x Must be a recessive allele B. For each pedigree, describe the genotypes of as many persons as possible. Most be X/x because of x/x Must be a recessive allele A/- A/a X/x x/Y X/- x/Y x/x X/Y X/x x/x X/Y X/x x/Y X/Y X/Y A/- A/- A/? A/? A/? A/a X/- x/Y X/- X/Y X/Y x/x A/a A/a x/Y x/Y x/x x/x a/a X/x x/Y x/Y