Page 106 - Genetics_From_Genes_to_Genomes_6th_FULL_Part3

400 Chapter 11 Analyzing Genomic Variation

26. Scientists were surprised to discover recently that d. Does any evidence exist for chimerism in the father
marmosets, a kind of monkey, are often chimeric— of the twins? in the mother?
they have cells that originated from two different zy- e. Explain how the biological mother of a baby mar-
gotes. Marmoset chimeras occur in fraternal twins. moset can be its genetic uncle. (Note: This is not
While in their mother's womb, these twins can share necessarily the situation for any of the baby mar-
cells through the blood supply because their placentas mosets in the figure.)
are fused. Any organ or tissue, including the germ
line, can be chimeric.
To determine if a particular male fathered any of Section 11.4
four baby marmosets from three different mothers,
DNA fingerprinting of four SSR loci was performed 27. The microarray shown in Problem 25 analyzes ge-
using genomic DNA from hairs. In the accompanying nomic DNA from a nuclear family in which the fa-
diagram, the thickness of the bands correlates with ther, one son, and one daughter have rare, late onset
the amount of DNA present. You can use the dots on polycystic kidney disease; while the mother, the sec-
both sides of the diagram, along with a ruler or paper ond son, and the second daughter are unaffected. As
edge, to help compare the positions of the bands. stated in Problem 25, the eight SNP loci examined are
evenly spaced at about 10 Mb intervals on chromo-
some 4, and they are shown on the microarray in their
Male Baby 1 Baby 2 Baby 3 Baby 4 actual order on this chromosome.
a. Is the allele responsible for the disease dominant or
Red Red recessive with respect to wild type? Is the disease
gene autosomal or X-linked?
b. For each of the four siblings, indicate the genotype
Blue Blue of the sperm from which they were created. For
each of these sperm, write the alleles for each of
the eight loci on chromosome 4 in order.
Green Green c. Identify the two SNP loci that are uninformative in
this family (that is, you cannot determine whether or
not either of these loci is linked to the disease gene).
Purple Purple d. Assuming for the sake of simplicity that the four
children shown would be completely representative
even if the parents had 100 children, the data in the
figure indicate that one locus is unlinked to the dis-
a. What is the maximum number of different alleles ease gene. Which one?
of any one SSR locus that the hair cells of any one e. The microarray results indicate that during meio-
marmoset could have? sis in the father, two different crossovers occurred
b. Which of the four babies could have been fathered in the region including the disease gene and the
by the male whose DNA fingerprint is shown? SNP loci that are genetically linked to it. Draw a
c. Identify the pair of chimeric fraternal twins. map of chromosome 4 showing the locations of