Higher Biology Unit 1 DNA and the Genome

Higher Biology Unit 1 DNA and the Genome KEY AREA 7: Evolution

DNA and the Genome Learning Intentions KEY AREA 7 – Evolution 1. Evolution 2. Selection 3. Speciation

7 a) Evolution is the process of changes in organisms over generations as a result of genomic variation It involves the processes of inheritance, selection, and speciation Inheritance can occur by vertical transfer or horizontal transfer Vertical transfer is when genetic information is passed from parent to offspring, either by sexual reproduction or asexual reproduction Horizontal transfer is when Genes are transferred between individuals in the same generation: this is quite common in prokaryotes

7 b) Natural Selection Natural selection is the non-random increase in in frequency of DNA sequences that increases survival It is also the non-random decrease in deleterious (harmful) sequences Stages of natural selection: 1. Too many offspring born 2. Struggle for survival until reproductive age 3. Better adapted survive, reproduce & pass on favourable genes to offspring 4. Less well adapted die & do not pass on genes to offspring

7 c) Natural Selection

7 d) Types of Selection The changes in phenotype frequency can be due to one of three things: 1. Stabilising selection 2. Directional selection 3. Disruptive selection When a polygenic trait is graphed, it often graphs as a bell-shaped normal distribution

7 e) Stabilising Selection In stabilising selection, the average is selected for Extremes of the phenotype are selected against There is a reduction in genetic diversity It occurs in unchanging environments On the graph, the peak becomes higher, and the edges are closer together Examples of stabilising selection are: 1. Natural human birth mass 2. Number of eggs laid by a female bird 3. Plant height

7 f) Directional Selection In directional selection, one extreme of the phenotype range is selected for It occurs during environmental change On the graph, the distribution curve shifts to the left or to the right Examples of directional selection are: 1. Increase in black bear size during ice ages 2. Artificial selection e. g. cow milk yield

7 g) Disruptive Selection In disruptive selection, two or more phenotypes are selected for The population becomes split into two distinct groups It occurs when two or more habitats become available The peak decreases in the middle and the edges increase into peaks Examples of disruptive selection are: 1. Breeding Chihuahuas and Great Danes 2. Beak sizes in Darwin’s finches on the Galapagos Islands

7 h) Natural Selection in Prokaryotes are able to exchange genetic material by horizontal transfer This means that they can evolve faster than organisms that only use vertical transfer, since they don’t have to wait for mutations to occur Horizontal gene transfer can be risky: the prokaryotes cannot pick and choose what genetic material it takes If the new gene is beneficial, the prokaryote will improve its chances of survival If the new gene is deleterious, the prokaryote is more likely to die

7 i) Speciation A species is a group of organisms that are able to interbreed and produce fertile offspring; members do not normally breed with other groups Speciation is the formation of a new species by evolution It occurs after isolation, mutation and selection Isolation barriers prevent gene flow between sub-populations during speciation There are two types of speciation that you need to know about: Allopatric speciation Sympatric speciation (Be aware that there are other ways to define a species other than the biological species concept above, such as morphology, ecology, genetics, and phylogeny)

7 j) Allopatric Speciation Allopatric speciation is caused by GEOGRAPHICAL isolation barriers You should be able to name some examples of geographical barriers from N 5 Different mutations will occur at random in each population Selection pressures acting on each group will be different leading to natural selection affecting the groups in different ways The two groups eventually become genetically distinct and isolated

7 k) Sympatric Speciation Sympatric speciation is caused by behavioural or ecological barriers The two populations live close to each other in the same environment but exploit different resources Examples of sympatric speciation are: 1. North American fruit flies 2. Darwin’s finches

7 l) Sympatric Speciation

7 m) Anole Lizards Anole lizards live in trees and found mostly in the warmer parts of the Americas Different species of anole lizards have developed different traits that allow them to live in their various habitats Youtube video: The Phylogenetic Tree of Anole Lizards https: //www. youtube. com/watch? v=rd. ZO wy. Dby. L 0

DNA and the Genome Questions KEY AREA 7 – Evolution 1. Testing Your Knowledge 1 P 84 Q 1 -4 except Q 3 b 2. Testing Your Knowledge 2 P 92 Q 2 -3 3. Problem Solving 4. Quick Quiz P 18 -22 Q 1 -7