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

SELECTION

Artificial Selection = genetic changes within a population which occur because human beings intentionally select for certain characteristics either by choosing which organisms to breed or eliminating undesirable individuals. Natural Selection = genetic changes within a natural (wild) population which occur because of differences in the reproductive success of some individuals over other individuals.

Artificial Selection

Why doesn’t selection work anymore on running speed? There are probably diseases involved. Too much inbreeding causes genetic defects. There is no more genetic variation in the alleles determining running speed. Epistatic effects are now in play. 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? Homology Mutation Genetic recombination (crossover) Sexual reproduction Migration (gene flow) 30

How Effective Is Selection? Consider Artificial Selection

All of these plants come from wild mustard !

Artificial Selection Farm animals (e.g. chicken egg production) 126 eggs/hen/year Today 365 eggs/hen/year

Milk Production

Artificial Selection in Dogs

Dogs mtDNA indicates that all dogs are derived from a species of wolf ~10,000 BC in Eurasia. The Romans (2,000 yrs. ago had 6 only breeds In 1837 the book British Quadrupeds listed < 20 breeds Now, ~200 breeds Most developed in the last 150 yrs.

EVOLUTION CAN BE FAST ! Over 200 breeds

Domestication of silver foxes Dmitri Belyaev Artificial Selection

Domestication of silver foxes

Pleiotropy

Domestication of silver foxes

NATURAL SELECTION 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. Negative selection= a selective disadvantage for a allele and that tends to disappear from the population.

NATURAL SELECTION IN BACTERIA Development of antibiotic resistance in bacteria

e.g. NATURAL SELECTION IN BACTERIA Resistance to antibiotics

e.g. NATURAL SELECTION IN BACTERIA Resistance to antibiotics

The Plague Deaths

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

NATURAL SELECTION OF PLANTS TO Herbicides

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

WHAT PRODUCES SELECTION? Internal Environment e.g. genetic environment (society of genes) e.g. physiological/developmental environment External Environment Physical Environment (water, temp., 02,) Biological Environment Competition Predation Parasitism Food supply Mate selection (Sexual Selection)

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

Small selective advantages Suppose there were a selective advantage to having a long nose and suppose that advantage produced a trend so the average nose length increased 0.001 inch/ year. How many inches will the nose will have grown in 100,000 years? One Ten 100 1,000 None of the above

Slight advantages over long time = Enormous changes!

SELECTION IN 2 ALLELE TRAITS Selection against a dominant trait Genotypes: AA Aa aa Rapid elimination of the trait should occur. Speed depends on how deleterious the allele is.

Fitness & Natural Selection How to calculate relative fitness Compare the success of the favored allele to that of the unfavored allele. W= number of children produced by 100 unfavored genotype number of children produced by 100 favored genotype

W= 20/100= 0.20 = fitness coefficient e.g. Achondroplastic Dwarfism Due to a dominant allele DD and Dd = dwarf condition dd = normal Number of children per 100 dwarf parents = 20 Number of children per normal parents = 100 W= 20/100= 0.20 = fitness coefficient

If the w= 20/100 = 0.2 the fittness value of the unfavored allele, what is the fittness value for the “favored allele”? Zero 0.2 0.5 1.0 None of the above

Selection in two allele systems Continued Selection against the recessive Genotypes: AA Aa aa 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 Normal allele C causes channels in the cell membranes (lung, gut) to allow Cl- out of cells and H20 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; affects 1 out of 2,500 white babies 5% of Caucasians are carriers CC is normal Cc is normal, but carrier cc has cystic fibrosis

If two carriers have children, what are the chances that their child will have cystic fibrosis? 100% 75% 50% 25% Zero %

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

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

Sickle Cell Co-dominance Normal Mild Anemia Severe Anemia HbN HbN HbN HbS HbS HbS 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! The environment determines what is fit!

Natural Selection in Polygene Traits Directional Selection

Natural Selection in Polygene Traits Stabilizing Selection

Natural Selection in Polygene Traits Disruptive Selection

What kind of selection is this? Directional Stabilizing Disruptive Eliminative No way to tell

This is negative selection— elimination of “unfit” genotypes.