MIT Biology Department 7.012: Introductory Biology - Fall 2004 Instructors: Professor Eric Lander, Professor Robert A. Weinberg, Dr. Claudette Gardel 7.012 Solutions to Linkage & Pedigrees Problem I. a) & b) One way to solve this problem is to work out the genotypes of the individuals in thepedigree. O + most likely configuration A – O – O – also possible, but less likelyA + O – B + (the only A + because the 2 affected children must receive a A – possibility) chromosome, which requires AB O B (+/+ most likely assumption) = B + chromosome from mom recomination in this individual. A����������������O O – O + 2 (the only possibility) 1 A O AA chromosome from dad O -3 4 (the only possibility) chromosome from mom A – = chromosome from dad O -AB B A O (the only possibility) chromosome from mom A – O – A – O – (the only possibilities)= chromosome from dad B + B + O – O – c) Individual 3 received an O - chromosome from dad and the B + chromosome from mom. d) To have type B blood, the child must have gotten an O - chromosome from mom and a B ? chromosome from dad. The recombination frequency (RF) gives the probability of crossover (genetic exchange) betweentwo genes. In the case of individual (3), he can produce 4 types of gametes: • B – recombinant • B + parental • O + recombinant • O – parental In order to be diseased and B, recombination must have occurred and since the recombinantion frequency is 11% (see first paragraph), the chance of being B and diseased is 11%.II. a) What are the genotypes of Phil and Ryan with respect to these two genes. Use the letter E forear wiggling and the letter R for tongue rolling. Phil E + Ryan + + + R + + b) How do you account for the fact that Ryan is unable to roll his tongue or wiggle his ears? During meiosis in Phil, there was recombination between the chromosome carrying the ability to wigglegene and the one carrying the ability to roll gene. E + --> E R and + + + R Ryan received the wildtype chromosome from his mother and the recombined completely wildtypechromosome from his
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