Chapter 15 – Mechanisms of Evolution AP Biology Chapter 15 – Mechanisms of Evolution

15.1 Why is evolution the unifying principle in biology? Things change all the time These changes drive the origin of species These changes drive the extinction of species These changes drive the diversity of life Evolution is change over time

15.1 #2 What was the significance of Lamarck’s ideas? His ideas led to the field of epigenetics – which is the study, in the field of genetics, of phenotypic trait variations that are caused by external or environmental factors that switch genes on and off and affect how cells read genes instead of being caused by changes in the DNA sequence

If Lamarck was right….

15.1 What was the mechanism Lamarck proposed? is the idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring (also known as heritability of acquired characteristics)

15.1 How does the present knowledge of molecular biology and genetics refute his mechanism? Traits are passed down by genes and DNA, and changes in DNA (mutations) not by acquired characteristics

15.1 Summarize Darwin’s theory of evolution by natural selection Species change over time Divergent (different) species share a common ancestor What produces change in species is natural selection – the differential survival and reproduction of individuals in a population based on variation in their traits

15.1 #6 What was the significance of Darwin’s theory of evolution by natural selection? It provided the first, and only explanation of the existence of adaptations in nature. It got proven and accepted after Mendel’s statistical analysis of genetic traits.

Bozeman Biology Write down the evidence of evolution on your sticky note and add to notes. Evidence of Evolution 10 minutes

15.2

What affects the genetic makeup of populations over time? Mutations – any change in DNA Artificial Selection – selecting certain breeds for breeding on purpose Natural Selection – survival and reproduction of the fittest Gene Flow – Arrival and Leaving of species in a population Genetic Drift – Change in genes due to random chance Nonrandom Mating – Mating with preference

Natural Selection acts on individuals, but populations evolve  The fittest organisms in a population are those that are strongest, healthiest, fastest, and/or largest. Natural selection is about survival of the very fittest individuals in a population. Natural selection produces organisms perfectly suited to their environments. Individual organisms do not evolve, they retain the same genes throughout their life. When a populationis evolving, the ratio of different genetic types is changing -- each individual organism within apopulation does not change. ... Individuals are selected. Populations evolve.

4. What is the difference between natural selection and adaptation? Difference in fitness among organisms Enhances the fitness of the organism Like a trait

Raw material Mutations

Populations evolve Changes in the genetic makeup of organisms over time

7. What is genetic drift? When is genetic drift especially potent in small populations? Random changes in allele frequencies from one generation to the next Small populations are affected the most because the random changes have a larger effect

8. What is the net affect of a population bottleneck? Loss of genetic variation

What are some potential causes of a population bottleneck? Hunting Habitat destruction Disease

Founders Effect Random changes in allele frequencies resulting from establishment of a population by a very small number of individuals.

Sexual Selection Organisms phenotype influences its ability to attract males

1. Fill out the chart Hardy Weinberg Equations P + Q =1 P2 + 2PQ + Q2 = 1 Required Conditions for HW Equilibruim No net mutations No natural selection No gene flow Large population size Random Mating

2. What is the significance of the HW equilibrium? It allows us to see if evolution is occurring in a population

Summarize the effect of the following on allele frequencies Mutations If dominant mutation, p goes up; If recessive mutation, p goes down etc. Gene Flow Emmigration would lower p and q; Immigration would increase p and q Genetic Drift Random – p and q would change either way Non-Random mating Chosen traits (dominant or recessive) would go up Natural Selection Best fit traits for survival (dominant or recessive) would go up

10.Define sexual selection Preference by 1 sex for certain characteristics

2 Bozeman Videos Genetic Drift 12 minutes Microevolution – 8 minutes

Bozeman Biology Hardy Weinberg 12 minutes

15.4 and 15.5 Ap Bio

Why do phenotypic variations in a population generally resemble a bell curve? Because mutations occur and society stabilizes populations Heavy babies sometimes don’t survive The lower weight babies sometimes don’t survive

Type of Natural Selection Effect and Example Stabilizing Selection Reduces variation (weight of babies is an example; height of humans is an example) Directional Selection One extreme is favored (giraffe neck length is an example) Disruptive Selection Both extremes are favored over mean (peppered moth is an example)

Bozeman Biology Selection 12 min.

15.5 Define fitness. How is fitness determined? Contribution of a genotype or phenotype to the gene pool It is determined by selection – the more “fit” you are, the more you are “selected” for and chosen for reproduction

Neutral Mutations Heterozygote Advantage Describe each. Many mutations are never observed, because they are lethal and therefore those individuals are removed from the population; neutral mutations are not beneficial or detrimental so they have no effect on fitness. Heterozygote Advantage Because heterozygotes have both alleles, heterozygote advantage maintains both alleles, therefore maintaining genetic variation.