Page 103 - Genetics_From_Genes_to_Genomes_6th_FULL_Part3

Problems 397

b. Assuming that these results indicate a trend, what
380 bp can you conclude about the processes that give rise
to mutant HD alleles? In what kinds of cells do
these processes take place?
270 bp c. How do these results explain why approximately
5–10% of Huntington disease patients have no
family history of this condition?
220 bp
d. Predict the results if you performed this same PCR
200 bp analysis on single skin cells from each of these
A B C D E F patients instead of single sperm.

17. Sperm samples were taken from two men just begin- Section 11.3
ning to show the effects of Huntington disease.
Individual sperm from these samples were analyzed 18. In 1993, the courts for the first time accepted plant
by PCR for the length of the trinucleotide repeat re- DNA as evidence in a murder trial. The accused de-
gion in the HD gene. In the graphs that follow, the fendant owned a pickup truck in which the police
horizontal axes represent the number of CAG re- found a few seed pods from a Palo Verde, the state
peats in each sperm, and the vertical axes represent tree of Arizona. The murdered woman was found
the fraction of total sperm of a particular size. The abandoned in the Arizona desert. How could a prose-
first graph shows the results for a man whose mutant cutor use DNA from the seed pods to build a strong
HD allele (as measured in somatic cells) contained case against the defendant?
62 CAG repeats; the man whose sperm were ana- 19. a. It is possible to perform DNA fingerprinting with
lyzed in the second graph had a mutant HD allele SNPs instead of SSRs as DNA markers, but in
with 48 repeats. general you would need to examine more SNP
markers than the 13 SSRs used in the CODIS data-
0.24 base to be sure of a match. Explain why.
0.22 b. DNA fingerprinting has been used to verify pedi-
0.20 grees of valuable animals such as show dogs, racing
0.18 greyhounds, and thoroughbred horses. However, the
0.16 technology is much harder to apply in these cases
0.14 than it is in forensic applications for humans. In par-
0.12 ticular, many more DNA markers must be examined
0.10 in domesticated animals to establish the identity or
0.08 close familial relationship of two DNA samples.
0.06 Why would you need to look at more polymorphic
0.04 loci in these animals than you would in humans?
0.02
20. On July 17, 1918, Tsar Nicholas II; his wife the
0 20 40 60 80 100 120 140 Tsarina Alix; their daughters Olga, Tatiana, Maria,

0.24 and Anastasia; their son, the Tsarevitch (Crown
0.22 Prince) Alexei; and four loyal retainers were mur-
0.20 dered by Bolshevik revolutionaries. The bodies were
0.18 not recovered for many years, fueling legends that
0.16 Grand Duchess Anastasia had escaped, and allowing
0.14 a woman named Anna Anderson to claim that she was
0.12 Anastasia. In 1991 and in 2007, two mass graves with
0.10 a total of nine skeletal remains were unearthed at
0.08 Ekaterinburg in Russia’s Ural Mountains. The table
0.06 that follows presents partial DNA fingerprint analysis
0.04 (using only five SSR loci and the sex chromosome
0.02 marker Amel) of these skeletons. Entries separated by
commas indicate alleles (number of repeating units).
0 20 40 60 80 100 120 140
a. What is the most likely identification for each skel-
a. What is the approximate CAG repeat number in eton? (Note: You cannot differentiate among any of
+
the HD alleles from both patients? the daughters based on this information alone.)