HOMEWORK: For each of the children A-F below, indicates whether their parents could be (1) #1 only, (2) #2 only, (3) #1 or #2 (but not both), (4) both #1 and #2, (5) neither #1 or #2.

Principle: From basic Mendelian genetics, we know that for each gene, every individual has two alleles (which may be identical), one of which was inherited from the mother and one from the father. Therefore, in a DNA fingerprint comprising a series of bands each of which corresponds to a single allele at a single microsatellite locus, a child must share exactly one band per locus with either parent, and the contributions of the two parents must complement each other (i.e., one band comes from one parent and one from the other parent). The band sharing coefficient between parent and offspring must be exactly 0.5.

    The example includes four alleles at the Blu locus (top to bottom: B1, B2, B3, & B4) and two at the Gry locus (G1 & G2). Parent #1 (the mother) has the genotype B1,B4 / G2,G2, and Parent #2 (the father) B2,B3 / G1,G2.

Child A = B1,B2 / G2,G2:The B1 and B2 alleles are shared with Parent #1, and B2 and the alternative B2 allele are shared with Parent #2. The fingerprint is consistent with Child A being the child of Parents 1 & 2.

Child B = B2,B2 / G1,G1:The child does not share a band with Parent #1 at either the Blu or Gry locus, but share B2 and G1 with Parent #2. Parent #1 is ruled out, Parent #2 is included. Note that lack of band sharing at either locus would rule out Parent #1.

Child C = B1,B1 / G1,G1:The G1 allele is not shared with Parent #1, and the G1 alleles is not shared with Parent #2. Both parents are ruled out. Note that the data from both loci are necessary to make the decision.

Child D = B1,B4 / G1,G1:The G1 allele is not shared with Parent #1, and neither A allele is shared with Parent #2. Both parents are ruled out, by the same logic as with Child C.

Child E = B4,B4 / G2,G2:The child shares bands B4 and G2 with Parent #1, and the alternative G2 with Parent #2, but does not share either A band with Parent #2. Parent #1 is included, Parent #2 is ruled out.

Child F = B2,B4 / G2,G2:The child shares bands B4 and G2 with Parent #1, and the alternative G2 as well as the B2 with Parent #2. Both Parents are included.

HOMEWORK: Draw a fingerprint pattern that would show that either Parent #1 or Parent #2 could be the true parent, but not both simultaneously.