Mutation as an Evolutionary Force 1.It occurs when errors are made in duplicating alleles in producing the gametes. 2.It is one of the weaker evolutionary forces, because errors are relatively rare. The error rate or mutation rate, , in copying an allele of a nuclear gene is ~ 1 x to 1 x It changes allele frequencies in a population and this change in the genetic composition of a population from parents to offspring is what we mean by evolution.

No Mutation AA Parents produce only ‘A’ bearing gametes. Aa Parents produce ½ ‘A’ and ½ ‘a’ bearing gametes aa Parents produce only all ‘a’ bearing gametes. With Mutation AA Parents produce some ‘a’ bearing mutant gametes. Aa Parents produce ½ ‘A’ and ½ ‘a’ gametes aa Parent produce some ‘A’ bearing mutant gametes.

Offspring population = A alleles = a alleles Parent population Reproduction With Mutation

How strong is mutation as an evolutionary force? Calculate how much the frequency of an allele changes in the population as a result of mutation. A a μ Mechanism of Mutation Allele in the Parent Mutant Allele in the Gamete and then In the Offspring Aa  Allele in the Parent Mutant Allele in the Gamete and then In the Offspring

Change in allele frequency,  P a, as a result of mutation A a μ Mechanism of Mutation Parent Frequencies: {P A, P a } Offspring Frequencies: {P A ’, P a ’}  Reproduction With Mutation How similar are P A ’ and P A ?

P a ’ = (1- v) P a + μ P A The change in allele frequency,  P a, caused by mutation Freq of a allele in offspring after mutation Non-Mutation rate times the Freq of a before mutation Mutation rate from A to a times the Freq of A before mutation ΔP a = P a ’– P a = μ – (  +  )P a Parent Frequencies: {P A, P a } Offspring Frequencies: {P A ’, P a ’} Reproduction With Mutation

An Evolutionary Equilibrium occurs when  P = 0 Evolution: change in allele frequency in a population from one generation to the next.  P > 0 the allele is increasing in frequency  P < 0 the allele is decreasing in frequency No Evolution : No change in allele frequency in a population from one generation to the next.  P = 0 the allele is neither increasing nor decreasing in frequency The Equilibrium Allele Frequency, P*, is the frequency that makes  P = 0

Set ΔP a = 0 = μ – (  +  )P a * Solve for P a * The change in allele frequency,  P a, caused by mutation ΔP a = P a ’– P a = μ – (  +  )P a What is the Equilibrium Allele Frequency, P a *?

The Equilibrium Allele Frequency,P a *, that makes  P a = 0 At the Mutation Equilibrium, ΔP a = 0. 0 = μ – (  +  )P a * P* a = μ/(  +  ) The Equilibrium Allele Frequency = Rate at which A is wrongly copied as a, Relative to all errors of copying at this gene.

Parent Population YY Yy yy Offspring Population YY Yy yy YYYyyy YY Offspring Yy yy Female Parents Male Parents {G YY, G Yy, G yy }, {P Y, P y } {G YY, G Yy, G yy }, {P Y, P y }

Parent Population YY Yy yy Offspring Population YY Yy yy {G YY, G Yy, G yy }, {P Y, P y } Y Y Y Y Y Y Y Y Y Y Y Y Y Y y y y y y yyy y y y y y y y y y y y y y y Gametes: Sperm + Eggs Gametes are mixed by Ocean Currents For pelagic spawners and broadcast spawners {G YY, G Yy, G yy }, {P Y, P y }

Pelagic eggs - eggs that float in the water column, like most deep water marine fishes and coral reef fishes. Pelagic Scatterers – spawn by scattering eggs and sperm into the water in schools near surface. For example:sardines, mackerel, tuna, whitefish. Broadcast Spawners: another name for forming zygotes by scattering eggs and sperm into the water Examples: Thunnus thynnus, atlantic blue fin tuna 10 feet long, weigh up to 1,400 pounds, lifespan longer than 20 years. the largest bony fish in the world; they migrate up to 5,000 miles. 0.8 to 2.6 million eggs per spawning female (roughly 100,000 eggs/kg). Eggs are ~ 1 mm in diameter and buoyant, enclosed in an oil droplet. LABRIDAE (WRASSES) All species are proto-gynous hermaphrodites: Females have the capacity to turn into males. Males are either born as males or are older sex-reversed females. Star Fishes.

Parent Population YY Yy yy Offspring Population YY Yy yy {G YY, G Yy, G yy }, {P Y, P y } Y Y Y Y Y Y Y Y Y Y Y Y Y Y y y y y y yyy y y y y y y y y y y y y y y Gametes: Sperm + Eggs Gametes are mixed by Ocean Currents For pelagic spawners and broadcast spawners {G YY, G Yy, G yy }, {P Y, P y }

Parent Population YY Yy yy Offspring Population YY Yy yy Female Gametes Male Gametes {G YY, G Yy, G yy }, {P Y, P y } {G YY, G Yy, G yy }, {P Y, P y } YPYYPY yPyyPy Y P Y YY ( P Y ) 2 Yy P Y P y y P y Yy P Y P y yy ( P y ) 2 Random Mating = Random Union of Gametes

Human Blood Groups: Number of Individuals: MM MN NN Total ,129 Genotype Frequencies: Number of Alleles: M N Total ,258 Allele Frequencies: Predicted Genotype (0.539) 2 2(0.539)(0.461) (0.461) 2 Frequencies from HWE Actual Observed

Human Blood Groups are in Hardy-Weinberg Equilibrium Predicted Genotype (0.539) 2 2(0.539)(0.461) (0.461) 2 Frequencies from HWE Actual Observed Conclude: Humans are mating at random with respect to blood groups! Conclude: No evidence of natural selection or any other evolutionary forces acting on these alleles. Conclude: We are mating like pelagic spawners as far as this gene is concerned! Conclude: Nonrandom mating can be occurring for some traits and genes but not others in the same population.