Page 100 - Genetics_From_Genes_to_Genomes_6th_FULL_Part3

394 Chapter 11 Analyzing Genomic Variation

PROBLEMS

Vocabulary have on the estimate of the rate of base substitu-
1. Choose the phrase from the right column that best fits tions in humans, and on your answer to part (b)?
the term in the left column. 5. If you examine Fig. 11.5 closely, you will note that in
some regions, such as between nucleotides 116,870 K
a. DNA polymorphism 1. DNA element composed of short
tandemly repeated sequences and 116,890 K, James Watson and Craig Venter share
b. phase 2. two different nucleotides appear the same SNPs, and these regions are surrounded by
at the same position in genomic others in which these two men do not share any SNPs.
DNA from different individuals What does this fact say about the relationship between
c. informative cross 3. arrangement of alleles of two these two men, and how do you think this pattern of
linked genes in a diploid shared and unshared SNPs arose?
d. ASO 4. location on a chromosome 6. Approximately 50 million SNPs have thus far been
e. SNP 5. a DNA sequence that occurs in recorded after the characterization of thousands of
two or more variant forms human genomes.
f. DNA fingerprinting 6. a short oligonucleotide that will a. About how many base pairs in the human genome
hybridize to only one allele at a
chosen SNP locus are identical in these thousands of people?
g. SSR 7. detection of genotype at a b. Do you think that many other SNPs exist among the
number of unlinked highly human population? If so, why haven’t they been found?
polymorphic loci c. Almost all of the SNP polymorphisms found to date
h. locus 8. allows identification of a gamete as are biallelic; that is, among all the genomes in the
recombinant or nonrecombinant population studied to date, only two possible alleles
i. compound 9. all exons in a genome can be found (for example, A and C). Provide a
heterozygote rough estimate for the number of triallelic SNP loci
j. exome 10. individual with two different that could be found in the same group of humans
mutations in the same gene
(that is, the number of loci with three different
alleles—for example, A, C, and T). At about how
Section 11.1 many loci would all four possible nucleotides be
2. Would you characterize the pattern of inheritance of found among the human genomes studied to date?
anonymous DNA polymorphisms as recessive, domi- 7. Mutations at simple sequence repeat (SSR) loci occur
nant, incompletely dominant, or codominant? at a frequency of 1 × 10 per locus per gamete,
−3
3. Would you be more likely to find single nucleotide which is much higher than the rate of base substitu-
−8
polymorphisms (SNPs) in the protein-coding or in the tions at SNP loci (whose frequency is about 1 × 10
noncoding DNA of the human genome? per nucleotide pair per gamete).
4. A recent estimate of the rate of base substitutions at a. What is the nature of SSR polymorphisms?
−8
SNP loci is about 1 × 10 per nucleotide pair per b. By what mechanism are these SSR polymorphisms
gamete. likely generated?
a. Based on this estimate, about how many de novo c. Copy number variants (CNVs) also mutate at a rel-
mutations (that is, mutations not found in the ge- atively high frequency. Do these mutations occur
nomes of your parents) are present in your own ge- by the same or a different mechanism than that
nome? generating SSRs?
b. Where and when did these de novo mutations in d. The SSR mutation rate is much higher than the
your genome most likely occur? mutation rate for new SNPs. Why then have geneti-
c. It has been calculated that each sperm made in a cists recorded more than 50 million SNP loci but
25-year-old man is the result on average of about only about 100,000 SSR loci in human genomes?
300 rounds of cell division, starting with the first 8. Humans and gorillas last shared a common ancestor
mitotic division of the male zygote. In contrast, about 10 million years ago. Humans and chimps last
each mature oocyte found in a 5-month-old female shared a common ancestor about 6 million years ago.
human fetus is the result of about 25 rounds of di- The table that follows shows the corresponding ge-
vision, starting with the first mitotic division of the nomic region from two gorilla gametes, three chim-
female zygote. What bearing do these calculations panzee gametes, and three human gametes.