Genetics: Analysis and Principles 5th Edition by Robert Brooker

Exercise 20

Take a look at solved problem S1 and the codon table found in Chapter 13 (Table 13.1). Assuming that a mutation involving a single-base change is more likely than a double-base change, propose how the Asn-141, Ile-141, and Thr-141 codons arose. In your answer, describe which of the six possible serine codons is/are likely to be the primordial serine codon of the globin gene family and how that codon changed to produce the Asn-141, Ile-141, and Thr-141 codons.Solved Problem S1
To answer this question, you will need to look back at the evolution of the globin gene family, which is shown in Chapter 8, Figure 8.7. Throughout the evolution of this gene family, mutations have occurred that have resulted in globin polypeptides with similar but significantly different amino acid sequences. If we look at the sequence alignment in Figure 23.10, we can make logical guesses regarding the timing of mutations, based on a comparison of the amino acid sequences of family members. What is/are the most probable time(s) that mutations occurred to produce the following amino acid differences Note: You need to examine the alignment in Figure 23.10 and the evolutionary time scale in Figure 8.7 to answer this question
a. Val-111 and Cys-111
B. Met-112 and Leu-112
C. Ser-141, Asn-141, Ile-141, and Thr-141
FIGURE 8.7 The evolution of the globin gene family in humans. The globin gene family evolved from a single ancestral globin gene. The first gene duplication produced two genes, one that encodes myoglobin (on chromosome 22) and a primordial hemoglobin gene that duplicated several times to produce several -chain and -chain genes, which are found on chromosomes 16 and 11, respectively. The four genes shown in gray are nonfunctional pseudogenes.
a.
FIGURE 23.10 A multiple sequence alignment among selected members of the globin gene family in humans.

a.
Table 13.1 The Genetic Code