16–2 Evolution as Genetic Change Section Outline Section 16-2 16–2 Evolution as Genetic Change A. Natural Selection on Single-Gene Traits B. Natural Selection on Polygenic Traits 1. Directional Selection 2. Stabilizing Selection 3. Disruptive Selection C. Genetic Drift D. Evolution Versus Genetic Equilibrium 1. Random Mating 2. Large Population 3. No Movement Into or Out of the Population 4. No Mutations 5. No Natural Selection

Natural Selection on Single-Gene Traits traits can lead to changes in _____ __________ and thus to ________. In a hypothetical population of lizards, individuals mostly demonstrate a brown _________, which is ________, so brown lizards are ________ ___ or __, and make up 80% of the population. Natural selection single-gene allele frequencies evolution phenotype dominant genotype BB Bb

Natural Selection on Single-Gene Traits 20% of the lizard population show the black _________, which arose as a result of a non-lethal ____ ____ _______, and are ________ __. According to _____-________, the ______ ________ of the recessive allele q is _____ or _____, so… phenotype germ cell mutation genotype bb Hardy Weinberg relative frequency 0.447 44.7%

Natural Selection on Single-Gene Traits the _______ ________ of the dominant p allele is _____. Because of the black lizards’ darker color, they absorb more heat from the sun, so they warm up faster on cool days, allowing them to move faster to avoid predation. After 30 generations, the black relative frequency 55.3%

Natural Selection on Single-Gene Traits _________ makes up ___ of the lizard population, so the frequency of the ________ q allele is now 77.5%. The change in the frequency of the alleles indicates ________ caused by ______ ________. phenotype 60% recessive evolution natural selection

Natural Selection on Polygenic Traits In ________ _____, ______ _______ can affect a population in three ways: _________ ________, ________ ________, and ________ ________. polygenic traits natural selection directional selection stabilizing selection disruptive selection

Figure 16–6 Graph of Directional Selection Section 16-2 Key Directional Selection Low mortality, high fitness High mortality, low fitness Food becomes scarce. Birds in the population with larger, stronger beaks find food in the large seeds available in the population, while birds with smaller beaks have a hard time getting enough food. Over time, birds with larger beaks make up most of the population.

Figure 16–7 Graph of Stabilizing Selection Section 16-2 Male birds use their plumage to attract mates. Male birds in the population with less brilliant and showy plumage are less likely to attract a mate, while male birds with showy plumage are more likely to attract a mate. Stabilizing Selection Male birds with showier, brightly- colored plumage also attract predators, and are less likely to live long enough to find a mate. The most fit, then, is the male bird in the middle-- showy, but not too showy. Key Low mortality, high fitness High mortality, low fitness Selection against both extremes keep curve narrow and in same place. Percentage of Population Brightness of Feather Color

Figure 16–8 Graph of Disruptive Selection Section 16-2 Disruptive Selection Largest and smallest seeds become more common. Key Low mortality, high fitness Population splits into two subgroups specializing in different seeds. Number of Birds in Population Number of Birds in Population High mortality, low fitness Beak Size Beak Size Something like a change in the climate causes medium-sized seeds to become scarce in the environment. Birds with smaller beaks are better at finding smaller seeds, and birds with larger beaks are better at finding larger seeds, while birds with medium-sized beaks (most of them) have trouble finding smaller and larger seeds. Over time and many generations, the bird population may even become two separate species.

If you flip a coin, there is a ___ chance Genetic Drift If you flip a coin, there is a ___ chance of the coin coming up heads. If you flip the coin 100 times, about __ should be heads. If you flip the coin 4 times, you are supposed to get _ heads, but you probably won’t, because the sample size is small. _______ ____ is a change in _____ ________ due to random chance, especially in small populations. 50% 50 2 Genetic drift allele frequency

Genetic Drift: Founder Effect Section 16-2 Sample of Original Population A population of beetles shows a wide variety of colors and patterns. A storm randomly blows a few individuals from the population to two new isolated locations, like two different islands. The few individuals become the founders of new populations, which don’t look much like the original. Descendants Founding Population A Founding Population B

Genetic Drift: Founder Effect Section 16-2 Sample of Original Population Descendants Founding Population A Founding Population B

Genetic Drift: Founder Effect Section 16-2 The two populations look very different from each other and the original, but it was random chance that made them that way. Sample of Original Population Descendants Founding Population A Founding Population B

Evolution vs. Genetic Equilibrium The _____-________ principle states that allele frequencies will remain ________ unless one or more factors cause those frequencies to change. If those factors are not present, allele frequencies remain constant, and a _______ __________ exists. Hardy Weinberg constant genetic equilibrium

Evolution vs. Genetic Equilibrium Five conditions are required to maintain _______________: genetic equilibrium 1. random mating 2. large population 3. no movement in or out 4. no mutations 5. no natural selection

Evolution vs. Genetic Equilibrium In order for ______ ______ to occur, all members of the population must have equal opportunity to produce offspring. In natural populations, like ____, ______, ___, or _____________, members compete or even fight for the opportunity to mate. random mating lions wolves elk mountain sheep

Evolution vs. Genetic Equilibrium For _______ __________ to occur, a population must be large, so _______ ___ doesn’t cause changes in allele frequency by random chance. No migration can occur, since movement in and out of the population changes the ________ of ______. genetic equilibrium genetic drift frequency alleles

Evolution vs. Genetic Equilibrium For _______ __________ to occur, there must not be _________, which introduce new ______, and no ______ ________ can take place which gives any one _________ a survival advantage over another. In some populations, these conditions may be met or nearly met over long periods of time, and little or no ________ occurs. genetic equilibrium mutations alleles natural selection phenotype evolution

Should the Use of Antibiotics Be Restricted? Read the Issues in Biology article on p. 403 in your text. Then watch the video Why Does Evolution Matter Now? and discuss the question: Should the use of antibiotics be restricted?