Genetics And Evolution, Lecture 8

Front 1

1) What are the different characteristics of mutations? And can mutations change allele frequencies to a significant degree?

Back 1

1) •All genetic variation is originally dueto mutations,noevolution without mutations!

•Mutations are rare

•Mutations can be

•somaticor in the germline

•advantageous, neutralor deleterious

•Population genetics:

•Fateof mutations

•Themutation itself does not change allele frequencies to a significant deg.ree, other processes need toact

Front 2

1) Name 4 processes which can determine the fate of a new mutation?

Back 2

1) Negative selection, Positive selection, neutral drift (increase or decrease in allele frequency by chance, by genetic drift- Genetic drift describes random fluctuations in the numbers of gene variants in a population), and fixation ( fixation is the change in a gene pool from a situation where there exists at least two variants of a particular gene (allele) to a situation where only one of the alleles remains).

Front 3

1) What is genetic drift?

2) How does it's importance change with population size?

Back 3

1) •Random change of allele frequencies fromgeneration to generation.

2) The larger the population the less important genetic drift is.

Front 4

1) What is a genetic bottleneck?

2) What is the founder effect?

Back 4

1) •A large population is reduced to a fewindividuals.

•Rare alleles are lost.

•Change of allele frequencies by chance.

2) A few individuals start a new population e.g- colonization of an island.

Front 5

1) What is the neutral theory?

2) What is gene flow? Effect on the receiving population?

Back 5

1) •Much DNA variation appears to be have noeffects on fitness and is therefore neutral.

•No selection acts on this variation.

•Genetic drift acts on these alleles andis therefore important in molecular evolution.

2) •Geneflow: movement of alleles from one population to another

•Increasesgenetic diversity in the receiving population

•Homogenisesconnected populations

•Canbe maladaptive

Front 6

1) Features that might define a species?

2) What is the Biological Species Concept and what are the problems with it?

Back 6

1) •Reproductive isolation from other species

•Species form morphological and/or geneticclusters that are distinct from other such clusters

•Members of a species share a commonancestor

•Group that is adapted toa particular ecological niche

2) TheBiological Species Concept: A species is a group of actually orpotentially interbreedingnatural populations that arereproductively isolatedfrom other such groups.

Problems with this concept

•Difficultto test for reproductive isolation•Cannotapply to asexual organisms

•Cannotbe tested in extinct groups

Front 7

1) The genotypic cluster species concept?

2) What does speciation require, and define post and pre-zygotic?

Back 7

1) Aspeciesis a [morphologically or genetically] distinguishable group of individuals thathas few or no intermediates when in contact with other such clusters.

2) •Speciation requires the evolution of reproductiveisolation.

•Pre-zygotic(before fertilisation):e.g. behavioural isolation (no mating),incompatibility of reproductive organs

•Post-zygotic(after fertilisation):some type of genetic incompatibility (e.g- offspring is sterile).

Front 8

1) Define: Cladogenesis, allopatric, parapatric, sympatric, anagenesis.

Back 8

1) •New species form by splittingofexisting species.

Cladogenesis (phylogeny):evolutionarysplitting event where a parent species splits into two distinct species,forming a clade (= speciation(population biology) )

•allopatric: geographically isolated, reproductive isolation gradually evolves in two or more populations separated by a geographic battier, and on renewed contact the new species do not interbreed.

•parapatric: adjacent,

•sympatric: without spatial separation (host, time?). The speciation occurs without physical barriers.

•Inreality: a continuum between these geographic extremes

•New species form by change over time

Anagenesis : cumulativechangewithin lineage

Front 9

1) Key processes in allopatric speciation?

Back 9

1) Genetic drift acting independently in separate geographic areas.

•Divergent selection ifenvironmental conditions differ

•Different mutations occur

Speciationisa by-product of gradual processes causing divergence.

•Allopatrycan occur because of

•dispersal

•vicariance (geographicbarrier arises, for example in snapping shrimp which were geographically isolated by the movements of land masses, forming an eastern pacific population and a caribbean population.

Front 10

1) Peripatric speciation in New Guinea kingfishers?

2) What is parapatric speciation?

Back 10

1) Peripatric speciation is a mode of speciation in which a new species is formed from an isolated peripheral population, a section of a population moves to another isolated niche.

•Speciationdue to dispersal from a large area to smaller areas, e.g. islands

•Differentiationoften faster in the smaller populations because genetic drift has larger effect.

2) •No geographic barrier, but extreme changein environmental conditions. The parental range could be limited by environmental conditions, but range expansion with adaptation to new conditions could give rise to a new species. The populations can live adjacent to eachother.

Front 11

1) What is sympatric speciation and give example?

Back 11

1) The key process is disruptive selection, it has been controversial whether it can occur because gene flow homogenises populations. Sympatric speciation occurs when populations of a species that share the same habitat become reproductively isolated from each other. This speciationphenomenon most commonly occurs through polyploidy, in which an offspring or group of offspring will be produced with twice the normal number of chromosomes.

The apple maggot fly (Rhagoletis pomonella) isnative to eastern North America. It originallybred in the large fruits of hawthorn trees.

•Host races in Rhagoletes pomonella which spread from hawthorn to apple and then to cherry (host plant shifts).

Front 12

1) Adaptive radiation? And example?

Back 12

1) Unusually rapid evolutionarydiversification, accelarated bynatural selection.For example the higher the number of islands in the galapagos, the higher the number of finch species (more niches to occupy, geographic isolation). An ancestor finch from South America mainland gave rise to Seed eaters, Bud eaters (adapted to pulling buds off trees), an insect eaters. There has been recent genomic insights into the phylogeny, as the evolution of Darwin's finches was revealed by genome sequencing.

Front 13

1) Cospeciation?

2) What is disruptive selection (in sympatric speciation?)

Back 13

1) When two groups of organisms speciate in response to eachother at the same time. E.g- Chewing lic and pocket gophers, each species of chewing lice is specific to a certain species of pocket gopher and vice versa.

2) Disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the population is divided into two distinct groups. Thisis seen in many populations of animals that have multiple male mating strategies, such as lobsters. Large, dominant alpha males obtain mates by brute force, while small males can sneak in for furtive copulations with the females in an alpha male's territory. In this case, both the alpha males and the "sneaking" males will be selected for, but medium-sized males, which cannot overtake the alpha males and are too big to sneak copulations, are selected against.