What is evolution? Change through time Decent with modification Change in the genetic make-up of biological populations through time

How does evolution occur?

This does happen Natural Selection MUTATION SEX Fertilization CROSSOVER Genetic recombination HEREDITY NEW SPECIES NATURAL SELECTION VARIATION

Inheritance of Acquired Characteristics This doesn’t happen Inheritance of Acquired Characteristics ENVIRONMENT “NEED” USE & DISUSE HEREDITY NEW SPECIES

This doesn’t happen OR DOES IT? ENVIRONMENT “NEED” USE & DISUSE Epigenetics HEREDITY ? NEW SPECIES

POPULATION GENETICS NOW.....

POPULATION GENETICS= Study of the change in the allele frequency in a population through time Gene pool = total collection of the alleles of a gene in the population

Rabbit Island 1000 rabbits = 600 brown & 400 white 2 alleles & complete dominance Brown (B) dominant White (b) recessive 3 genotypes BB & Bb= Brown bb = white

Suppose 500 Homozygous brown rabbits BB = 1000 B alleles 100 Heterozygous brown rabbits Bb = 100 B alleles 100 b alleles 400 Homozygous white rabbits bb = 800 b alleles Total: 1100 B alleles 900 b alleles Or 55% B 45% b

Suppose the Allele Frequency in the Original Colonists was p = fraction of gene pool with dominant allele. (p= .55) q = fraction of gene pool with recessive allele. (q= .45) Total p + q = 1.00 (0.55) + (0.45) = 1.00

GENOTYPES in the NEXT GENERATION The frequency of drawing the BB genotype in the next generation is C) 0.3025 P2 = (0.55)2 = 0.3025 or about 30%

What is the frequency of the white genotype? Answer: E) None of the above q2 = (0.45)2 = 0.2025 or about 20%

What is the frequency of the Bb genotype? Answer: D) 0.4950 2 (pq) = 2 (0.55 x 0.45)= 0.4950 or about 50%

Hardy-Weinberg Principle p2 + 2pq + q2 = 1.0 BB Bb bb

HARDY-WEINBERG PRICIPLE Allele frequency & genotype frequency will remain constant from generation to generation if No natural selection No differential migration (no gene flow) No differential mutation Random mating Large population (no genetic drift or random genetic changes)

Hardy-Weinberg Principle p2 + 2pq + q2 = 1.0 BB Bb bb T h i s d e s c r i b e s t h e s i t u a t i o n W h en t h e r e I s N O e v o l u t I o n

Using the Hardy-Weinberg equation How many of you can roll your tongues? It is due to a dominant allele R She is either RR or Rr Non-rollers are rr

the gene pool is composed of only R’s & r’s, can you So 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr) Let us assume that there is no selective advantage to tongue rolling so that the Hardy-Weinberg conditions hold Now remembering that the gene pool is composed of only R’s & r’s, can you calculate what % of the gene pool is r and what % is R?

And if there are 400 students in this room how many are Rr?

ANSWER Remember p2 + 2pq + q2 RR + (Rr + rR) + rr If 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr) Remember p2 + 2pq + q2 RR + (Rr + rR) + rr 4% + 32% + 64% = 100%

And if there are 400 students in this room how many are Rr? 0.32 x 400 = 128

If a change in allele frequency does occur (i. e If a change in allele frequency does occur (i.e. there is evolution), then the rules of the Hardy-Weinberg Principle have been violated.

HARDY-WEINBERG PRICIPLE Allele frequency & genotype frequency will remain constant from generation to generation if No natural selection No differential migration (no gene flow) No differential mutation Random mating Large population (no genetic drift or random genetic changes)

Consider the problem of population size Random changes will be important in small populations (< 500 individuals). Small populations do not have a large number of possible variations in their alleles. 1. “Founder effect” during the founding of new colonies. 2. “Bottleneck effect” because of population crashes. 3. “Genetic drift” in small populations

The Founder Effect 1) Shuffle your deck of cards 2) Deal out 10 cards face down 3) Look at your cards and indicate how many red cards you have with your clicker

The Founder Effect 1) Shuffle your deck of cards 2) Deal out 10 cards face down 3) Look at your cards and indicate how many red cards you have with your clicker One Two Three Four Five Six Seven Eight Nine Ten

Founder Effect is the loss of genetic variation that occurs when a new population is established by a small number of individuals from a larger population The new population is only a sample of the original population diversity and may be drastically different. e.g. Genetic diversity of Icelanders, & Easter Island natives is much less than the population at large. e.g. Amish population established by only a few colonists and the prevalence of polydactyly is much higher than the original population.

Bottleneck Effect is the loss of genetic variation that occurs when a great decrease in the population size occurs. The new population is only a sample of the original population diversity and may be drastically different. e.g.The frequency of total color blindness among the inhabitants of Pingelap, an island in Micronesia. Around 1775, a typhoon reduced the population of the island to only 20. Among survivors, one of them was heterozygous for color blindness. After few generations, the prevalence of color blindness was 5% of population and 30% as carriers (in the USA, only 0.003% of the population has complete color blindness).

Genetic drift is the change in the frequency of a gene variant (allele) in a population due to random sampling. Take 10 cards, half red and half black. Mix thoroughly face down. Without looking at the faces of the cards, pick out ½ of the cards and return them to the deck. Count the number of red and black cards remaining and record the numbers. Simulate reproduction= For each card remaining, add one of the same color. This simulates asexual reproduction. Now you have 10 cards again. Repeat steps 2—6 for several generations. Stop when only one color is left (i.e. has become “fixed.”) “fixes

Effect of population size on random variation

But the Hardy-Weinberg Rule is seldom in effect “ The most tenacious misconception in biology may be the idea that all processes serve a purpose This idea is so deep-seated that students fail to even consider random processes as responsible for biological patterns” Genetic Drift is a random process and is responsible for many characteristics of populations. It happens in all populations, not just small ones, although the smaller the population the faster and more profound the effect is likely to be.

Now you know how to do it. Don’t you? First, figure out the recessive allele frequency and everything else follows!

Another Problem 5 10 18 405 None of the above There are 500 dragons in a population 495 are red and 5 blue Red is the dominant allele with complete dominance. How many dragons in the population carry the blue allele but are red? i.e. How many are Rr ? 5 10 18 405 None of the above

GOOD LUCK ON THE EXAM!