Page 66 - Genetics_From_Genes_to_Genomes_6th_FULL_Part3

360 Chapter 10 Genome Annotation

Answer b. These parents from North Africa both were homozy-
gotes for a deletion of one of the two Hbα genes.
a. Both of these parents from Southeast Asia must have Thus, all of their children would have α-thalassemia
been heterozygotes with one normal copy of the HbA (two Hbα genes instead of the normal four), and none
locus and the other copy deleted for both Hbα1 and of their conceptions would lead to hydrops fetalis.
Hbα2. One fourth of their conceptions would lead to Note that the genetic counselor could have given this
hydrops fetalis (homozygosity for the deletion), one advice only if the counselor knew from analysis of the
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half to α-thalassemia (Hbα1 Hbα2 / - -), one fourth parents’ genomes what kind of defects were present in
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to a normal situation (Hbα1 Hbα2 / Hbα1 Hbα2 ). their HbA loci.
PROBLEMS

Vocabulary These estimates for evolutionary events were obtained
in part by comparing the genomic sequences of vari-
1. Match each of the terms in the left column to the best- ous current-day species. The basic supposition behind
fitting phrase from the right column. these estimates is that of a molecular clock: Differ-
a. exome 1. a discrete part of a protein that provides a unit ences in particular types of genomic sequences accu-
of function mulate at a relatively linear rate during evolutionary
b. de novo gene 2. a nonfunctional member of a gene family time. Consider the three following kinds of nucleotide
c. gene desert 3. the joining together of exons in a gene in changes: (i) missense mutations in coding regions that
different combinations alter amino acid identity; (ii) silent (synonymous) mu-
d. pseudogene 4. most frequent residues, either nucleotide or tations that change a codon for a particular amino acid
amino acid, found at each position in a into a different codon for the same amino acid; and
sequence alignment (iii) mutations in introns. Which of the three types of
e. syntenic block 5. set of genes related by processes of mutations would . . .
duplication and divergence b. . . . represent the slowest-ticking clock? (That is,
f. orthologs 6. chromosomal region with the same genes in which type of mutation would accumulate the least
the same order in two different species rapidly in genomes? Hint: See Fig. 10.3.)
g. natural 7. genes with sequence similarities in two c. . . . you most likely use to estimate the divergence
selection different species that arose from a common
ancestral gene times of species that last shared a common ances-
h. consensus 8. genes that arose by duplication within a tor more than 400 million years ago?
sequence species d. . . . be most likely to vary in the rate at which they
i. gene family 9. genomic DNA sequences containing exons would accumulate in different genes?
j. paralogs 10. gene-poor region of the genome 4. Which of the enzymes from the following list would
k. alternative 11. recently evolved from intergenic DNA you need to make a cDNA library? What is the func-
RNA splicing sequences tion of those enzyme(s) in the process?
l. protein domain 12. progressive elimination of individuals whose a. DNA polymerase
fitness is low and survival of individuals of
high fitness b. RNA polymerase
c. A restriction enzyme
Section 10.1 d. DNA ligase
2. List three independent techniques you could use to e. An aminoacyl-tRNA synthetase
identify DNA sequences encoding human genes
within a cloned genomic region. f. Peptidyl transferase
3. Figure 10.2a has numbers indicating the approximate g. Reverse transcriptase
number of millions of years ago that species on separate 5. One of the following sequences was obtained from
branches of the tree last shared a common ancestor. a cloned piece of a genome that includes parts of
a. About how many millions of years ago did humans two exons of a gene. The other sequence was ob-
last share a common ancestor with chimpanzees, tained from the corresponding part of a cDNA clone
mice, dogs, chickens, and frogs? representing the mRNA for this gene. (Note: For