Natural selection is a major mechanism of evolution (1.A.1) Big Idea …edhsgreensea.net/APBiology/Unit_Review_PPT/APBio1A1.pdf · 2012-08-30 · AP Biology Curriculum 2012-2013 Big

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

Biology Eighth Edition

Neil Campbell and Jane Reece

AP Biology Curriculum 2012-2013

Big Idea 1: Evolution

Change in the genetic makeup of a population over time is evolution. (1.A.1.)

22.2, 23.2

a. According to Darwin’s theory of natural selection, competition for limited resources results in differential survival.

Natural selection is a major mechanism of evolution (1.A.1)


• Individuals with more favorable phenotypes are more likely to survive and produce more offspring, thus passing traits to subsequent generations (Descent With Modification).

“I think” Darwin’s 1837 sketch

b. Evolutionary fitness is measured by reproductive success (aka: Darwinian Fitness).


(a) Cactus-eater (c) Seed-eater

(b) Insect-eater

Beak Variation in Galapagos Finches


c. Genetic variation and mutation play roles in natural selection.

• A diverse gene pool is important for the survival of a species in a changing environment.


Variation in a population


d. Environments can be more or less stable or fluctuating,– and this affects evolutionary rate and direction; – different genetic variations can be selected in each

generation.



e. An adaptation is:– a genetic variation that is favored by selection and – is manifested as a trait that provides an advantage to an

organism in a particular environment. f. In addition to natural selection, chance and random events

can influence the evolutionary process, especially for small populations. (1.A.3)



PBS Evolving Ideas - video 4 How Do We Know Evolution Happens? (7:00 mins)http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.htmlhttp://www.youtube.com/watch?v=xkwRTIKXaxg

g. Conditions for a population or an allele to be in Hardy-Weinberg equilibrium are:

- 1. a large population size,

- 2. absence of migration,

- 3. no net mutations,

- 4. random mating and

- 5. absence of selection.

• These conditions are seldom met in real populations.



h. Mathematical approaches are used to calculate changes in allele frequency, providing evidence for the occurrence of evolution in a population.

– The Hardy-Weinberg principle describes a population that is not evolving.

– If a population does not meet the criteria of the Hardy-Weinberg principle, then it can be concluded that the population is evolving.



Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

• By convention, if there are 2 alleles at a locus, p and q are used to represent their frequencies

• The frequency of all alleles in a population will add up to 1

– For example, p + q = 1

• If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then– p2 + 2pq + q2 = 1– where p2 and q2 represent the frequencies of the

homozygous genotypes and 2pq represents the frequency of the heterozygous genotype

The Hardy-Weinberg Principle

Fig. 23-6

Selecting alleles at random from a gene pool

Frequencies of allelesAlleles in the population

Gametes produced

Each egg: Each sperm:

80%chance

80%chance

20%chance

20%chance

q = frequency of

p = frequency ofCR allele = 0.8

CW allele = 0.2

1) The allele frequencies of the population are 0.8 (80%) and 0.2 (20%).

2) If all of these alleles could be placed in a large bin, 80% would be CR and 20% would be CW.

3) Assuming mating is random, each time two gametes come together, there is an 80% chance the egg carries a CR allele and a 20% chance it carries a CW allele.

The Hardy-Weinberg principle

Fig. 23-7-4

Gametes of this generation:

64% CR CR, 32% CR CW, and 4% CW CW

64% CR + 16% CR = 80% CR = 0.8 = p

4% CW + 16% CW = 20% CW = 0.2 = q

64% CR CR, 32% CR CW, and 4% CW CW plants

Genotypes in the next generation:

SpermCR

(80%)

CW

(20%

)

80% CR ( p = 0.8)

CW (20%)

20% CW (q = 0.2)

16% ( pq) CR CW

4% (q2) CW CW

CR

(80%

)

64% ( p2) CR CR

16% (qp) CR CW

Eggs

If the gametes come together at random, the genotype frequencies of this generation are in Hardy-Weinberg equilibrium:

Gametes for each generation are drawn at random from the gene pool of the previous generation.

With random mating, these gametes will result in the same mix of genotypes in the next generation


• We can assume the locus that causes phenylketonuria (PKU) is in Hardy-Weinberg equilibrium given that:– The PKU gene mutation rate is low– Mate selection is random with respect to whether or not an

individual is a carrier for the PKU allele

• PKU metabolic disorder resulting from homozygosity for a recessive allele:– left untreated leads to mental retardation– newborns are tested for PKU at birth– symptoms can be lessened with a phenylalanine-free diet

Applying the Hardy-Weinberg Principle (p. 474-475)


• The occurrence of PKU is 1 per 10,000 births– q2 = 0.0001– q = 0.01

• The frequency of normal alleles is– p = 1 – q = 1 – 0.01 = 0.99

• The frequency of carriers is– 2pq = 2 x 0.99 x 0.01 = 0.0198– or approximately 2% of the U.S. population

Applying the Hardy-Weinberg Principle (p. 474-475)

YouTube - Bozeman Biology: Solving Hardy Weinberg Problems (11:00 min.)http://www.youtube.com/watch?v=xPkOAnK20kw&feature=plcp

YouTube - Bozeman Biology: Population Genetics and Evolution Lab (6:00 min.)http://www.youtube.com/watch?v=KmqgZvUoq3k&feature=plcp

YouTube - Bozeman Biology: Microevolution (7:00 min.)http://www.youtube.com/watch?v=lk4_aIocyHc&feature=plcp

Natural selection is a major mechanism of evolution (1.A.1) Big Idea …edhsgreensea.net/APBiology/Unit_Review_PPT/APBio1A1.pdf · 2012-08-30 · AP Biology Curriculum 2012-2013 Big

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