Problem 18
Consequence of Nucleotide Substitutions Suppose deoxycytidine (C) in one strand of DNA is mistakenly replaced with deoxythymidine (T) during cell division. What is the consequence for the cell if the deoxynucleotide change is not repaired?
Problem 19
Mutation and Protein Function Suppose that the gene for a protein 500 amino acids in length undergoes a mutation. If the mutation causes the synthesis of a mutant protein in which just one of the 500 amino acids is incorrect, the protein may lose all of its biological function. How can this small change in a protein's sequence inactivate it?
Problem 20
Gene Duplication and Evolution Suppose that a rare DNA replication error results in the duplication of a single gene, giving the daughter cell two copies of the same gene. a. How does this change favor the acquisition of a new function by the daughter cell? b. In the vascular plant Arabidopsis thaliana, \(50 \%\) to \(60 \%\) of the genome consists of duplicate content. How might this confer a selective advantage?
Problem 21
Cryptobiotic Tardigrades and Life Tardigrades, also called water bears or moss piglets, are small animals that can grow to about \(0.5 \mathrm{~mm}\) in length. Terrestrial tardigrades (pictured here) typically live in the moist environments of mosses and lichens. Some of these species are capable of surviving extreme conditions. Some tardigrades can enter a reversible state called cryptobiosis, in which metabolism completely stops until conditions become hospitable. In this state, various tardigrade species have withstood dehydration, extreme temperatures from \(-200{ }^{\circ} \mathrm{C}\) to \(+150{ }^{\circ} \mathrm{C}\), pressures from 6,000 atm to a vacuum, anoxic conditions, and the radiation of space. Do tardigrades in cryptobiosis meet the definition of life? Why or why not?
