Topic 10.3 – Gene Pools and Speciation Essential Idea: Gene Pools change over time. A Gene Pool is the collection of genes (and the alleles for them) present in an interbreeding population. A species is a set of interbreeding organisms that produce fertile offspring. Speciation is the process by which small differences between organisms in a single species lead to changes within a gene pool over time. The changes within a population are representative of allele frequency shifts, and these occur over time.

Evolution requires that allele frequencies change with time in populations. This concept is known as Genetic Drift. Allele Frequencies are represented by a number: 0.0 – 1.0 The higher the number, the greater the frequency within a population. Ex..3 = 30% of the population carry the allele. In the same way that the alleles shift in this population of rabbits, so did the alleles shift in our population of hand grabby aliens.

The Hardy – Weinberg Equation is a way to represent the change in allele frequency over time. In general, we represent the dominant allele as p, and the recessive allele as q. Total Frequency of all alleles must equal 1.0 Frequency of dominant allele(p) + frequency of recessive allele(q) = 1.0  p + q = 1.0 However, we have a combination of two alleles for each trait, so the frequency with respect to a trait is Allele #1 Allele #2 (p+q) X (p+q) = 1 Hardy – Weinberg Equation p 2 + 2pq + q 2 =1 Example: Dominant - R (p) Recessive – r (q) Number of Homozygous Dominant Individuals Number of Heterozygous Individuals Number of Homozygous Recessive Individuals Remember: Individuals who are RR (q 2 ) and Rr (2pq) will have the same phenotype, so it is important to start with the recessive phenotype.

The Hardy – Weinberg Equation is a way to represent the change in allele frequency over time. Sample Problem: There are a population of 1000 penguins, in which 12 penguins have blue feet (recessive trait). Calculate the allele frequency of the foot color alleles, and the number of individuals with each genotype in the population. Four Steps to solving any Hardy-Weinberg Problem 1.Assign alleles 1.Frequency of dominant is ‘p’ 2.Frequency of recessive is ‘q’ 2.Calculate q by taking the square root of the number of homozygous recessive individuals. 3.Calculate p (the allele frequencies must equal 1, so p = 1-q) 4.Use p and q to calculate the other genotype frequencies: 1.Freq. of homo. Dominant = p 2 2.Freq. of heterozygous = 2pq 3.Freq. of homo. Recessive = q 2 1.Yellow Feet = p Blue Feet = q 2. q 2 = 3. p = 1-q 4. p 2 = 2pq = q 2 =

Sample Problem: There are a population of 2,732 ogres, in which 248 ogres have layers (recessive trait). Calculate the allele frequency of the ‘having layers’ alleles, and the number of individuals with each genotype in the population. Work Space: Four Steps to solving any Hardy-Weinberg Problem 1.Assign alleles 1.Frequency of dominant is ‘p’ 2.Frequency of recessive is ‘q’ 2.Calculate q by taking the square root of the number of homozygous recessive individuals. 3.Calculate p (the allele frequencies must equal 1, so p = 1-q) 4.Use p and q to calculate the other genotype frequencies: 1.Freq. of homo. Dominant = p 2 2.Freq. of heterozygous = 2pq 3.Freq. of homo. Recessive = q 2

The Hardy – Weinberg Equation is a way to represent the change in allele frequency over time. Often times, the representation of allele frequency is done in a pie chart, since it is being discussed out of the total population.

Reproductive isolation of populations can be temporal, behavioral or geographic. Any of these mechanisms can lead to reproductive isolation, which in turn leads to speciation. SPECIATION Isolated species reproduce independently, leading to either: Sympatric Speciation: Still live in same area Allopatric Speciation: Live in different areas This process of speciation can either occur abruptly or gradually Behavioral Isolation Changes of courtship rituals, mating calls Temporal Isolation Difference of mating seasons Geographic Isolation Barriers between portions of population

Speciation can either be gradual or abrupt. Punctuated Change -Due to extreme environmental changes -Long periods where fossils are unable to be collected -Long periods of no change Gradual Change -Small changes over long periods of time -Each phenotype is represented as a part of the whole Devonian Extinction (75% Life) End Permian Extinction (97% Life) Triassic Extinction (50% Life)

Selection as a result of isolation can be either directional, stabilizing or disruptive. Directional Selection: Pushes the phenotypes towards one end of a continuum Stabilizing Selection: Removes individuals at the extremes of the phenotypes Disruptive Selection: Removes individuals from the middle of the phenotype. This pushes the species often into two new species.

Identify the type of selection present in the following scenarios. Giraffes used to have shorter necks. As time went on, extremely long necks were selected for and short or medium necks were selected against. A species of tropical land snail shows a polymorphism of opposite-coiling shells. Some snails in the species have shells that coil clockwise, and others are counter-clockwise. A species of birds is used to laying lightly colored eggs on the white pebbles of a beach, and has done so for many generations. The light color helps to hide the eggs from predators and it is extremely rare to see any dark eggs produced. Because of a volcanic eruption that covered the beach in black particles, this species of bird is now laying more and more dark colored eggs. Human babies demonstrate different body masses at birth, but a body mass that is too small would be disadvantageous to the survival of the baby. Too great of a body mass makes childbirth too difficult and can also reduce survival chances.

Polyploidy is a condition in which organisms contain more than two homologous sets of chromosomes. Organisms that exhibit polyploidy tend to be larger. This also holds true for plants. The genus Allium is comprised of many flowering plants, all stemming from the true organism, garlic. This polyploidy in the genus Allium leads to all of the different variety of plants we see currently. Garlic Chives Onion Shallots Leeks Diploid Pentaploid Diploid Triploid Quadraploid 2n = 16 5n = 40 2n = 16 3n = 24 4n = 32

Polyploidy can be used by cultivators to generate larger and larger offspring from their plants. It’s only a matter of time until the plants start to cultivate us! Farmers use diploid cells from parent plants and combine them to add genetic material to the progeny. More DNA = more chance for mutations.

Practice Problem – Data Analysis with geographically separated species. When a person’s blood type is O +, the positive sign refers to the presence of a characteristic known as the Rhesus factor, Rh. Having Rh factor (Rh+) is dominant to not having Rh factor (Rh-). This trait follows normal Mendelian Inheritance, in that persons with genotypes BB and Bb will be Rh+, and bb persons will be Rh-. There was a study conducted recently on the frequency of Rh factor in two geographically separated populations. Data shown below. In Lagos, Nigeria, a study with 23,382 people revealed 3% of the population was Rh -. In Abha, Saudi Arabia, a study with 944 males revealed 7.2% of the population was Rh -. 1.Use the Hardy –Weinberg equation to calculate the frequencies of the two alleles, B and b, in the two countries. 2.In the south-west of France, a study of 127 French Basque people found that the allele frequency for b to be How does this compare with the frequency of b in the other two populations?