MECHANISMS OF EVOLUTION LEARNING GOALS List and discuss

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MECHANISMS OF EVOLUTION

MECHANISMS OF EVOLUTION

LEARNING GOALS � List and discuss the mechanisms of evolution. � Differentiate between the

LEARNING GOALS � List and discuss the mechanisms of evolution. � Differentiate between the types of genetic drift. � List and describe the 4 types of natural selection � Discuss factors that influence speciation � Compare gradualism and punctuated equilibrium

MECHANISMS OF EVOLUTION 1. 2. 3. 4. 5. Natural Selection Gene Flow Genetic drift

MECHANISMS OF EVOLUTION 1. 2. 3. 4. 5. Natural Selection Gene Flow Genetic drift Mutations Non-random mating

ARTIFICIAL SELECTION � Domesticated breeds have not always been in their current form. This

ARTIFICIAL SELECTION � Domesticated breeds have not always been in their current form. This change has been achieved by repeatedly selecting for breeding the individuals most suited to human uses. This shows that selection cause evolution.

GENETIC VARIATION � � � individuals in a species carry different alleles (An allele

GENETIC VARIATION � � � individuals in a species carry different alleles (An allele is an alternative form of a gene (one member of a pair) that is located at a specific positionon a specific chromosome. Any change in gene (and allele) frequencies within a population or species is Evolution Allele Frequency – proportion of gene copies in a population of a given allele

1. NATURAL SELECTION: Affects variation in a population as the better adapted (more fit)

1. NATURAL SELECTION: Affects variation in a population as the better adapted (more fit) individuals to their environment survive and reproduce, passing on their genes to the successive generations increasing the frequency of favourable alleles in the population. � Nature “selects” which organisms will be successful �

NATURAL SELECTION � Imagine that green beetles are easier for birds to spot (and

NATURAL SELECTION � Imagine that green beetles are easier for birds to spot (and hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous generation.

NATURAL SELECTION

NATURAL SELECTION

DARK PEPPER MOTHS � http: //www. youtube. com/watch? v=Ly. RA 807 dj. Lc&feature=rel ated

DARK PEPPER MOTHS � http: //www. youtube. com/watch? v=Ly. RA 807 dj. Lc&feature=rel ated

REVIEW: 4 STEPS OF NATURAL SELECTION: 1. In nature, more offspring are produced than

REVIEW: 4 STEPS OF NATURAL SELECTION: 1. In nature, more offspring are produced than can survive. � 2. In any population, individuals have variation. � 3. Individuals with advantageous variations survive and pass on their variations to the next generation. � 4. Overtime, offspring with certain advantageous variations make up most of the population �

2. GENE FLOW: Is the movement of alleles into or out of a population

2. GENE FLOW: Is the movement of alleles into or out of a population (immigration or emigration). � Gene flow can introduce new alleles into a gene pool or can change allele frequencies. � The overall effect of gene flow is to counteract natural selection by creating less differences between populations. � Example: � � Plant pollen being blown into a new area

GENE FLOW � Gene flow is what happens when two or more populations interbreed.

GENE FLOW � Gene flow is what happens when two or more populations interbreed. This generally increases genetic diversity. Imagine two populations of squirrels on opposite sides of a river. The squirrels on the west side have bushier tails than those on the east side as a result of three different genes that code for tail bushiness. If a tree falls over the river and the squirrels are able to scamper across it to mate with the other population, gene flow occurs. The next generation of squirrels on the east side may have more bushy tails than those in the previous generation, and west side squirrels might have fewer bushy tails.

GENE FLOW Some individuals from a population of brown beetles might have joined a

GENE FLOW Some individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population.

3. GENETIC DRIFT � � § § The change in allele frequencies as a

3. GENETIC DRIFT � � § § The change in allele frequencies as a result of chance processes. These changes are much more pronounced in small populations. Directly related to the population numbers. Smaller population sizes are more susceptible to genetic drift than larger populations because there is a greater chance that a rare allele will be lost.

� Imagine that in one generation, two brown beetles happened to have four offspring

� Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation—but just by chance. These chance changes from generation to generation are known as genetic drift.

� In a population of 100 bears, suppose there are two alleles for fur

� In a population of 100 bears, suppose there are two alleles for fur color: A 1 (black) and A 2 (brown). A 1 has a frequency of. 9, A 2 a frequency of. 1 (1. 0 = 100%). The number of individuals carrying A 2 is very small compared to the number of individuals carrying A 1, and if only fifty percent of the population survives to breed that year, there's a good chance that the A 2 s will be wiped out.

EXAMPLES OF GENETIC DRIFT � A) The Founder Effect: A founder effect occurs when

EXAMPLES OF GENETIC DRIFT � A) The Founder Effect: A founder effect occurs when a new colony is started by a few members of original population. � Small population that branches off from a larger one may or may not be genetically representative of the larger population from which it was derived. � Only a fraction of the total genetic diversity of the original gene pool is represented in these few individuals.

FOUNDERS EFFECT � For example, the Afrikaner population of Dutch settlers in South Africa

FOUNDERS EFFECT � For example, the Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. This effect is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder events.

EXAMPLES OF GENETIC DRIFT � B) Population Bottleneck: � Occurs when a population undergoes

EXAMPLES OF GENETIC DRIFT � B) Population Bottleneck: � Occurs when a population undergoes an event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing. • The event may eliminate alleles entirely or also cause other alleles to be over -represented in a gene pool. EX. Cheetahs http: //www. nytimes. com/1985/09/17/science/loss-of-gene-diversity-is-threat-to-cheetahs. htm l

Bottleneck = any kind of event that reduces the population significantly. . . earthquake.

Bottleneck = any kind of event that reduces the population significantly. . . earthquake. . flood. . . disease. . . etc. …

BOTTLENECK � An example of a bottleneck: 
Northern elephant seals have reduced genetic variation

BOTTLENECK � An example of a bottleneck: 
Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890 s. Hunting reduced their population size to as few as 20 individuals at the end of the 19 th century. Their population has since rebounded to over 30, 000 but their genes still carry the marks of this bottleneck. They have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.

4. MUTATIONS � � � § § Are inheritable changes in the genotype. Provide

4. MUTATIONS � � � § § Are inheritable changes in the genotype. Provide the variation that can be acted upon by natural selection. Mutations provide the raw material on which natural selection can act. Only source of additional genetic material and new alleles. Can be neutral, harmful or beneficial( give an individual a better chance for survival). Antibiotic resistance in bacteria is one form.

� � � Mutation is a change in DNA the hereditary material of life.

� � � Mutation is a change in DNA the hereditary material of life. An organism’s DNA affects how it looks, how it behaves, and its physiology—all aspects of its life. So a change in an organism’s DNA can cause changes in all aspects of its life. Somatic mutations occur in non-reproductive cells and won’t be passed onto offspring. For example, the golden color on half of this Red Delicious apple was caused by a somatic mutation. The seeds of this apple do not carry the mutation.

The only mutations that matter to largescale evolution are those that can be passed

The only mutations that matter to largescale evolution are those that can be passed on to offspring. These occur in reproductive cells like eggs and sperm and are called germ line mutations. § A single germ line mutation can have a range of effects: 1. No change occurs in phenotype. §

2. Small change occurs in phenotype. 3. Big change occurs in phenotype. 
Some really

2. Small change occurs in phenotype. 3. Big change occurs in phenotype. 
Some really important resistance in insects are sometimes caused by single mutations 1. A single mutation can also have strong negative effects for the organism. Mutations that cause the death of an organism are called lethals —and it doesn't get more negative than that.

CAUSES OF MUTATIONS § DNA fails to copy accurately. § External influences can create

CAUSES OF MUTATIONS § DNA fails to copy accurately. § External influences can create mutations. § Mutations can also be caused by exposure to specific chemicals or radiation.

5. NON-RANDOM MATING In animals, non-random mating can change allele frequencies as the choice

5. NON-RANDOM MATING In animals, non-random mating can change allele frequencies as the choice of mates is often an important part of behaviour. � Many plants self-pollinate, which is also a form of non-random mating (inbreeding). �

Sexual reproduction results in variation of traits in offspring as a result of crossing

Sexual reproduction results in variation of traits in offspring as a result of crossing over in meiosis and mutations Genetic shuffling is a source of variation.

SEXUAL SELECTION Sexual selection occurs when certain traits increase mating success.

SEXUAL SELECTION Sexual selection occurs when certain traits increase mating success.

THERE ARE TWO TYPES OF SEXUAL SELECTION. – – intrasexual selection: competition among males

THERE ARE TWO TYPES OF SEXUAL SELECTION. – – intrasexual selection: competition among males intersexual selection: males display certain traits to females

PREZYGOTIC ISOLATION: An isolating mechanism that prevents reproduction by making fertilization unlikely POSTZYGOTIC ISOLATION

PREZYGOTIC ISOLATION: An isolating mechanism that prevents reproduction by making fertilization unlikely POSTZYGOTIC ISOLATION Fertilization has occurred but a hybrid offspring cannot develop or reproduce REPRODUCTIVE ISOLATION

SPECIATION: ADDITION OF SPECIES TO THE GENE POOL � Allopatric speciation: �A physical barrier

SPECIATION: ADDITION OF SPECIES TO THE GENE POOL � Allopatric speciation: �A physical barrier divides one population into two or more populations � EX: Physical barriers--Mountains, Grand Canyon � Sympatric �A speciation: species evolves into a new species without a physical barrier

PATTERNS OF EVOLUTION Adaptive Radiation Divergent evolution One species gives rise to many in

PATTERNS OF EVOLUTION Adaptive Radiation Divergent evolution One species gives rise to many in response to a new habitat or ecological opportunity Coevolution When species evolve in close relationship with one another Convergent Evolution Unrelated species evolve similar traits even though they live in different parts of the world Rate of Speciation Gradualism: evolution occurs in small, gradual steps Punctuated Equilibrium: rapid spurts of genetic change cause species to diverge quickly.

RATE OF SPECIATION

RATE OF SPECIATION