Chapter 16 Table of Contents Section 1 Genetic Equilibrium Population Genetics and Speciation Chapter 16 Table of Contents Section 1 Genetic Equilibrium Section 2 Disruption of Genetic Equilibrium Section 3 Formation of Species

Variation of Traits Population genetics - The study of evolution from a genetic point of view. Also known as microevolution - a change in the collective genetic material of a population. Remember a population is the smallest unit in which evolution can occur.

Variation of Traits Within a Population Section 1 Genetic Equilibrium Chapter 16 Variation of Traits Within a Population Population biologists study many different traits in populations, such as size and color.

Variation of Traits Within a Population, cont. Section 1 Genetic Equilibrium Chapter 16 Variation of Traits Within a Population, cont. Causes of Variation Traits vary and can be mapped along a bell curve, which shows that most individuals have average traits, whereas a few individuals have extreme traits. Variations in genotype arise by mutation (random change in a gene that is passes on), recombination (reshuffling of genes during meiosis due to crossing-over), and the random pairing of gametes (due to the large amounts if gametes).

Section 1 Genetic Equilibrium Chapter 16 The Gene Pool The total genetic information available in a population is called the gene pool. The number of alleles and frequency of those alleles in a gene. Allele frequency is determined by dividing the total number of a certain allele by the total number of alleles of all types in the population. Predicting Phenotype Phenotype frequency is equal to the number of individuals with a particular phenotype divided by the total number of individuals in the population.

Generation 1 What about generation 2? Phenotypic ratios 4 red (out of 8) frequency = .5, 4 pink (out of 8) frequency =.5, no white frequency = 0. Genotypic ratios 12 R (out of 16) frequency = .75 4 r (out of 16) frequency = .25 What about generation 2?

The Hardy-Weinberg Genetic Equilibrium Section 1 Genetic Equilibrium Chapter 16 The Hardy-Weinberg Genetic Equilibrium Allele frequencies in the gene pool do not change unless acted upon by certain forces. Hardy-Weinberg genetic equilibrium is a theoretical model of a population in which no evolution occurs and the gene pool of the population is stable. q+p=1 q2+2pq+p2=1 5 Assumptions for Equilibrium

Chapter 16 Causes of Evolution Section 2 Disruption of Genetic Equilibrium Chapter 16 Causes of Evolution Evolution may take place when populations are subject to genetic mutations, gene flow, genetic drift, nonrandom mating, or natural selection. Mutations are changes in the DNA. Some are harmful and difficult to eliminate, some are helpful, and increase survival.

Section 2 Disruption of Genetic Equilibrium Chapter 16 Gene Flow Emigration and immigration cause gene flow between populations and can thus affect gene frequencies. Immigration - Individuals moving into population. Emigration - Individuals moving out of a population Gene Flow - the process of genes moving from one population to another through migration or dispersal of seeds and spores.

Section 2 Disruption of Genetic Equilibrium Chapter 16 Genetic Drift Genetic drift is a change in allele frequencies due to random events. Genetic drift operates most strongly in small populations, but genetic equilibrium happens in large populations because a change is less effective Small population, one organism doesn’t mate it could be catastrophic. In large populations, one organism doesn’t mate, the population will still go on.

Chapter 16 Nonrandom Mating Section 2 Disruption of Genetic Equilibrium Chapter 16 Nonrandom Mating Mating is nonrandom whenever individuals may choose partners. Assortative mating - picking a mate that has similar genes to oneself. Sexual Selection Sexual selection occurs when certain traits increase an individual’s success at mating. Sexual selection explains the development of traits that improve reproductive success but that may harm the individual. Ex. Peacock mating

Chapter 16 Natural Selection Section 2 Disruption of Genetic Equilibrium Chapter 16 Natural Selection Natural selection can influence evolution in one of three general patterns. Stabilizing selection favors the formation of average traits. Disruptive selection favors extreme traits rather than average traits. Directional selection favors the formation of more-extreme traits.

Three Kinds of Selection Section 2 Disruption of Genetic Equilibrium Chapter 16 Three Kinds of Selection

Chapter 16 The Concept of Species Section 3 Formation of Species Chapter 16 The Concept of Species According to the biological species concept, a species is a population of organisms that can successfully interbreed but cannot breed with other groups. Ex. Dogs cannot breed with cats Speciation – The development of new species Morphology – the internal and external structure and appearance of an organism, used to classify it as a species.

Modern Definition of Species/Speciation Species – A single kind of organism. Members are morphologically similar and can interbreed to produce fully fertile offspring. The many species alive today diverged from a smaller group of species.

Isolation and Speciation Section 3 Formation of Species Chapter 16 Isolation and Speciation Geographic Isolation Geographic isolation the physical separation of members of a population by geographic barriers. Ex. Canyons or Mountains forming. Allopatric Speciation - the arrival of new species due to geographic isolation. Happens more often in small populations with a small gene pool because they are more greatly affected by the environment.

Chapter 16 Geographic Isolation Section 3 Formation of Species Click below to watch the Visual Concept. Visual Concept

Isolation and Speciation, continued Section 3 Formation of Species Chapter 16 Isolation and Speciation, continued Reproductive Isolation results from the separation of population subgroups by barriers to successful breeding. Disruptive Selection causes this to happen, 2 types of isolation from this. Prezygotic – before fertilization. (different mating times and calls of frogs.) Postzygotic – after fertilization. (horse and donkey.) Sympatric Speciation - Reproductive isolation within the same geographic area. Ex. If all of a species lives on one type of plant and then some individuals start to live on another plant, they may not longer be able to interbreed with their original population.

Reproductive Isolation Section 3 Formation of Species Chapter 16 Reproductive Isolation Click below to watch the Visual Concept. Visual Concept

Chapter 16 Rates of Speciation Slow over Millions of years Section 3 Formation of Species Chapter 16 Rates of Speciation Slow over Millions of years In the gradual model of speciation (gradualism), species undergo small changes at a constant rate. Quick Bursts of Change Under punctuated equilibrium, new species arise abruptly, differ greatly from their ancestors, and then change little over long periods.

Chapter 16 Comparing Punctuated Equilibrium and Gradualism Section 3 Formation of Species Chapter 16 Comparing Punctuated Equilibrium and Gradualism Click below to watch the Visual Concept. Visual Concept