Evolution, 4th Edition

PHEnoTyPiC EvoluTion 139 the genotype that is homozygous for the “big” allele at all 50 loci is expected to be (0.25)^100 ≈ 10 – ...

140 CHAPTER 6 The horned lizards give an example of directional selection, which favors either an increase or a decrease in a tr ...

PHEnoTyPiC EvoluTion 141 statistically significant, shows there was directional selection. Note that this comparison is between ...

142 CHAPTER 6 The opposite situation is called disruptive selection. Here the smallest and larg- est individuals have higher fit ...

PHEnoTyPiC EvoluTion 143 garter snake (Thamnophis ordinoides) varies in its color pattern: some individuals are striped, others ...

144 CHAPTER 6 frequency distribution of these gradients. Directional selection is common. In some cases, it is very strong: dire ...

PHEnoTyPiC EvoluTion 145 Both evolutionary biologists and breeders need to know how much the mean of a trait will evolve if ther ...

146 CHAPTER 6 The essential message from Equation 6.1 is that the rate of evolution depends both on the strength of inheritance, ...

PHEnoTyPiC EvoluTion 147 parents (see Figure 6.14). We can also use those measurements to find P, the phe- notypic variance of t ...

148 CHAPTER 6 using genetic variation that already exists, what is called standing genetic variation (see Chapter 5). Other trai ...

PHEnoTyPiC EvoluTion 149 salt. Initially, population sizes declined as the salt killed off yeast cells more rapidly than they we ...

150 CHAPTER 6 a critical contribution to society since it allows us to produce more food with the same or even fewer resources. ...

PHEnoTyPiC EvoluTion 151 Correlated Traits Traits are correlated: if you have long arms, you probably also have long legs. This ...

152 CHAPTER 6 Side effects like these may explain some evolutionary enigmas. The Mexican tetra (Astyanax mexicanus) is a fish th ...

PHEnoTyPiC EvoluTion 153 Earlier in the chapter we discussed the partridge-pea, which may not adapt quickly enough to avoid exti ...

154 CHAPTER 6 example, smaller individuals tend to have higher metabolic rates per body mass. A second source of genetic correla ...

PHEnoTyPiC EvoluTion 155 together by a series of chromosome inversions that prevent recombination from producing low fitness col ...

156 CHAPTER 6 the decrease in oxygen pressure. Among these changes is an increase in the concentration of red blood cells (RBCs) ...

PHEnoTyPiC EvoluTion 157 tomato with a much smaller wild relative. Several more generations of breed- ing among the hybrids prod ...

158 CHAPTER 6 and environmental effects on the phenotype are more difficult to control, much larger sample sizes are needed with ...