SELECTION

Why doesn’t selection work anymore on running speed? A) There are probably diseases involved B) Too much inbreeding producing genetic defects C) There is no more genetic variation in the stock D) Epistatic effects are now in play E) Artificial insemination programs inadvertently select for defective (weaker) sperm.

In order for Evolution to Occur there must be variation in the population

Which is NOT a cause of allele variation in a population? A) Homology B) Mutation C) Genetic recombination (cross over) D) Sexual recombination E) Migration (gene flow)

SO Selection & Genetic drift Selection & Genetic drift working on variation in the population cause

How Effective Is Selection? Consider Artificial Selection

In fact, all of these plants Come from wild mustard !

Artificial Selection cont’. Farm animals (e.g. chicken egg production) Farm animals (e.g. chicken egg production) eggs/hen/year Today 365 eggs/hen/year

Artificial Selection in Dogs

Dogs All dog fossils from 10,000 years ago are from one species of Asian Wolf All dog fossils from 10,000 years ago are from one species of Asian Wolf The Romans (2,000 yrs ago) had 6 breeds The Romans (2,000 yrs ago) had 6 breeds All other breeds have been developed in the last 400 years !!!!! All other breeds have been developed in the last 400 years !!!!!

NATURAL SELECTION Differences in mortality & reproduction lead to differences in the proportion of alleles passing to the next generation. Differences in mortality & reproduction lead to differences in the proportion of alleles passing to the next generation. Positive selection= a selective advantage for one allele and that favored allele increases in the population. Positive selection= a selective advantage for one allele and that favored allele increases in the population. Negative selection= a selective disadvantage Negative selection= a selective disadvantage for a allele and that tends to disappear from the population. for a allele and that tends to disappear from the population.

NATURAL SELECTION IN BACTERIA Development of antibiotic Development of antibiotic resistance in bacteria

e.g. NATURAL SELECTION IN BACTERIA Resistance to antibiotics

e.g. NATURAL SELECTION IN INSECTS Resistance to pesticides Foliate Foliateinsecticide

NATURAL SELECTION OF PLANTS TO Herbicide Year Deployed Resistance Observed

NATURAL SELECTION IN PLANTS FOR COPPER TOLERENCE Please look at the video. Please look at the video.

WHAT PRODUCES SELECTION? Internal Environment Internal Environment –e.g. genetic environment –e.g. physiological/developmental environment External Environment External Environment –Physical Environment (water, temp., 0 2,) –Biological Environment  Competition  Predation  Parasitism  Food supply  Mate selection (Sexual Selection)

Success must be judged in 2 ways: Absolute Terms= Will the genome work? Absolute Terms= Will the genome work? Relative Terms= Is the genome the best Relative Terms= Is the genome the best available model?

Small Selective Advantages Suppose that there were a selective advantage to having a long nose and suppose there was a trend that the average nose length increased 0.001/year Suppose that there were a selective advantage to having a long nose and suppose there was a trend that the average nose length increased 0.001/year How many inches will the nose grow in 100,000 years? How many inches will the nose grow in 100,000 years? A) 1.0 B) 10 C) 100 D) 1000 E) None of the above.

SELECTION IN 2 ALLELE TRAITS Selection against a dominant trait Selection against a dominant trait Genotypes: AA Aa aa Rapid elimination of the trait should occur.

Acondroplastic Dwarfism Acondroplastic Dwarfism Caused by dominant allele D

Fitness & Natural Selection How to calculate fitness How to calculate fitness Compare the success of the favored allele to that of the unfavored allele. e.g. Acondroplastic dwarfism (dominant allele) W= number of children produced by 100 dwarfs number of children produced by 100 normals number of children produced by 100 normals W= 20/100= 0.20 = fitness coefficient for dwarfs

Clicker Question If W= 20/100= 0.20 is the fitness coefficient for dwarfs If W= 20/100= 0.20 is the fitness coefficient for dwarfs What is the fitness coefficient of the normal individuals? A) Zero B) 0.2 C) 0.5 D) 1.0 E) None of the above

Answer Remember that the fitness of the best allele is always = 1.0 Remember that the fitness of the best allele is always = 1.0 Since the normals produce more offspring than the dwarfs, they have a Since the normals produce more offspring than the dwarfs, they have a W = 1.0 Dwarfism would rapidly be eliminated from the population if it were not for its high mutation rate!

Selection in two allele systems Cont’. Selection against the recessive Selection against the recessive Genotypes:AAAaaa Selection will be slow to remove the “a” allele in complete dominance because it is hidden in the heterozygous condition “Aa.” These are carriers.

Cystic Fibrosis Caused by recessive trait, cc Caused by recessive trait, cc Normal allele C, causes channels in the cell membranes (lung, gut) to allow Cl- out of cell Normal allele C, causes channels in the cell membranes (lung, gut) to allow Cl- out of cell H 2 0 follows. If both alleles are cc, then this doesn’t happen & thick sticky mucus clogs lungs & gut & these tissues are breeding ground for bacteria

Cystic Fibrosis Most common genetic disorder in Caucasians; Most common genetic disorder in Caucasians; affects 1 out of 2,500 white babies 5% of Caucasians are carriers 5% of Caucasians are carriers CC is normal CC is normal Cc is normal, but carrier Cc is normal, but carrier cc has cystic fibrosis cc has cystic fibrosis

Clicker Question If two carriers have children, what are the chances that their child will have CF? If two carriers have children, what are the chances that their child will have CF? A) 100% B) 75% C) 50% D) 25% E) Zero %

Cystic Fibrosis Cc x Cc = 25% of kids are cc & have Cystic Fib. Cc x Cc = 25% of kids are cc & have Cystic Fib. Why aren’t they eliminated from the pop? Why aren’t they eliminated from the pop? –Because Cc have protection against diarrhea ?

Selection in two allele systems Cont’. Selection favoring heterozygotes “Aa” Selection favoring heterozygotes “Aa” Can only occur if incomplete or co-dominance because the trait must be expressed. e.g. Sickle-cell anemia

Sickle Cell Co-dominance Normal Mild Anemia Severe Anemia Normal Mild Anemia Severe Anemia Hb N Hb N Hb N Hb S Hb S Hb S In the USA: W = 1.0 W = 0.9 W = 0.14 In Africa: W = 0.88 W = 1.0 W = 0.14 Heterozygotes are favored in Africa because they are more resistant to malaria!

Natural Selection in Polygene Traits Directional Selection

Natural Selection in Polygene Traits Stabilizing Selection

Natural Selection in Polygene Traits Disruptive Selection

Natural Selection in Humans What kind of selection is this? What kind of selection is this? A) Directional B) Stabilizing C) Disruptive D) None of the above E) No way to know