evolution chapter 11. slide 2 of 30 do penguins reproduce asexually or sexually? what does this...

Evolution

Chapter 11

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Do penguins reproduce asexually or sexually?

What does this tell us about these penguins?

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Basketball Team Analogy

You want to put together a winning basketball team. Do you want a large or small number of people to show

up for tryouts? Do you want students from one school or from multiple

schools? Do you care if the players have mothers or fathers, etc.

who played basketball? Do you care about the hair color of the players?

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Guiding Questions

What is the nature of genetic variation in populations?

How do biologists measure variation in a population?

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Population

Population – a group of members of the same species in the same area

Phenotype – a trait produced by one or more genes

In a population, there will likely be a range of phenotypes

Natural selection works on phenotypes, not genotypes Example, even though some contract HIV, they have no

symptoms Penguins that are better swimmers will get food when it is

in short supply

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Population (Page 2)

Genetic variation is stored in a population’s gene pool

Gene pool – the combined alleles of all the individuals in a population

Allele Frequency – measure of how common an allele is in a population A population consists of 5 individuals: 4 homozygous

dominants (AA), 4 Heterozygotes (Aa), & 2 Homozygote Recessive (aa)

What is the frequency of the A allele? What is the frequency of the a allele?

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Question 11.1

1. What is the relationship between allele frequencies and a gene pool?

2. How did Mendel manipulate the gene pool of pea plants in his experiments? What are the allele frequencies in P generation?

Assume equal numbers of both purebreeds F1 generation? F2 generation?

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Sources of Genetic Variation?

1. Mutation Random change in a gene What are the two main type of mutations? ONLY mutations in which types of cells are capable of

being passed on? More individuals = more mutations More mutations = ____ genetic variation More genetic variation = ______ population

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Sources of Genetic Variation?

2. Recombination Meiosis

There are 2 main sources of genetic variation, what are they?

Fertilization When the egg is fertilized by the sperm, we get a brand

new combination of chromosomes In each pair of homologous chromosomes, 1 chromosome

is from ____ and the other is from ____

Section 11.2

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Populations, not individuals, Evolve

Populations are characterized by a wide range of phenotypes

Think of height, there are a few who are very tall and a few who are very short But most are intermediate in height

What type of inheritance results in a range of phenotypes?

Normal curve (Bell Curve) – graph of the frequency of each of the phenotypes in a population

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So which phenotype is best?

If there is no better phenotype, then the trait will approximate a normal curve

Most phenotypes are normally distributed anyway

However, environmental conditions can change and favor certain phenotypes

So natural selection will lead to evolution in a population Evolution is a change in allele frequencies of a population

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Natural Selection = 1 of 3 changes

Natural Selection can lead to microevolution

Microevolution – observable change in allele frequencies of a population over time

3 Patterns: 1. Directional Selection 2. Stabilizing Selection 3. Disruptive Selection

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1. Directional Selection

Favors ONLY 1 of the phenotypic extremes

An extreme phenotype becomes common

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2. Stabilizing Selection

Intermediate phenotypes are selected for

BOTH phenotypic extremes are selected against

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3. Disruptive Selection

BOTH extreme phenotypes are selected for

Intermediate phenotypes are selected against

Section 11.3

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Other Mechanisms of Evolution

1. Gene flow Immigration & Emigration

2. Gene Drift Random changes in allele frequencies

3. Sexual Selection Traits that are not naturally adaptive, but enable

successful reproduction

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Gene Flow

Movement of alleles from one gene pool or population to another

Movement of alleles INTO a gene pool = increased genetic variation

Movement of alleles OUT of a gene pool = decreased genetic variation

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Genetic Drift

Flip a coin 6 times, how many times should be heads, but how many times are actually heads?

Requires small population size

Results in a loss of population genetic diversity

2 processes that shrink a population enough to produce gene drift Bottleneck Effect Founder Effect

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Bottleneck Effect

A population bottleneck is an event that greatly reduces the population

The population bottleneck can result in genetic drift

A reduction in population size leads to a type of genetic drift called the Bottleneck Effect In turn leads to a change in allele

frequencies

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Bottleneck Examples

1. Elephant seals were hunted down to 20 individuals Population rebounded to 100,000 but little genetic

variation New population was essentially inbred

2. Natural disaster reduces a population size Hurricane kills off most of the insects on an island, but

the few who survive look radically different than those on the mainland. Over time the island population grows back, but looks entirely different than the mainland population

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Founder Effect

A type of Genetic drift that occurs after a small number of individuals colonize a new area

Results in a loss of genetic variation

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Sexual Selection

Sexual selection occurs when certain traits increase mating success

There are 2 types of sexual selection: Intrasexual selection:

Competition among males Intersexual selection:

Males display certain traits to females in courtship

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Intrasexual Selection Intersexual Selection

evolution chapter 11. slide 2 of 30 do penguins reproduce asexually or sexually? what does this...

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