This problem was on the final exam of our new Fundamentals of Genetics course. It's an example of what I'd like our students to be able to do.
(10 points) The ideogram above shows a normal child’s genome, with her chromosomes coloured by 23andMe to show the results of genotyping her DNA and the DNAs of her maternal grandparents. Blue segments indicate blocks of alleles shared with her maternal grandmother, and white segments indicate blocks of alleles shared with her maternal grandfather. Hatched segments could not be analyzed because they have too few SNPs.
a. (1 point) What genetic process is responsible for these blocks of alleles?
b. (2 points) When and where did this process occur?
c. (2 points) What property of the child’s maternal chromosomes 11 and 14 is unexpected? Why is this property unexpected?
d. (4 points) Suggest two different kinds of events that could explain this unexpected property. Give rough estimates of the probabilities of the events you propose.
e. (1 point) The black triangles above some chromosomes show the locations of SNPs linked to effects on nose shape. What do these predict about the child’s appearance?