5.4 EVOLUTION

Ms. TRS

5.4.1 - Define evolution•The cumulative change

in the heritable characteristics of a

population or

•The changes in allelic frequencies in the gene

pool of a population over time, as a result of

natural selection, genetic drift, gene flow, and mutation pressure.

Evidence of Evolution• 5.4.2 - Outline the evidence for evolution by the fossil record, selective

breeding of domesticated animals and homologous structures

• Fossil record• Homologous structures• Selective breeding

Fossils are the mineralized remains of organisms that lived in the past.

The study of fossil skeletons allows inferences about form and function and clearly suggests a process of gradual change over time.

Selective breeding

Domesticated breeds have been developed by selecting desirable traits, and breeding from them

Selective Breeding• Man has selectively bred animals and plants for thousands

of years.• If an animal posses a characteristic that is considered useful

or valuable then this animal is selected for breeding.• The hope then is that this characteristic will be present in

the next generation and at a higher frequency than before.In subsequent generations it may even then be possible to

select from an even more advantageous characteristicThe observations of artificial selection (selective breeding)

suggested that natural populations would:Show phenotypic variationBe subject to natural selection pressuresThere would be selection of those individuals possessing the advantageous characteristic

Homologous structures: vertebrate embryos and the pentadactyl limb.

homologous structures: various different structures sharing the same fundamental plan

-derived from a similar embryonic origin -variations on the basic structure allow different functions adaptive radiation = permitting exploitation of different ways of life suggests divergence from a common ancestor

a) Humerusb) Radiusc) Ulna

•In each example the bones are modified and adapted to the locomotion of the animal

•The fact that the basic shape and position of the bones is similar suggest that they have a common ancestor

•In the whale there is no real need for the fingers as they can still swim without them, this could suggest common ancestry with the other five-fingered organisms

Homologous structures

Homologous Structure?

What structure do these two have in common?

5.4.3 - State that populations tend to produce more offspring than the environment can support5.4.4 - Explain that the consequence of the potential overproduction of offspring is a struggle for survival5.4.5 - State that members of a species show variation5.4.6 - Explain how sexual reproduction promotes variation in species5.4.7 - Explain how natural selection leads to evolution

Natural selection

• Darwin’s theory of Evolution• Overproduction• Competition• Struggle for existence • Survival of the fittest• Natural selection

Populations tend to produce more offspring than the environment can

support.

Consequence of the potential overproduction

• Struggle for survival

observation 1: All species have such great potential fertility that their population size would increase exponentially if all individuals that are born reproduced successfully observation 2: Populations tend to remain stable in size except for seasonal fluctuations. observation 3: Environmental resources are limited. inference 1: Production of more individuals than the environment can support leads to a competition for resources like food and space among individuals of a population, predation, parasitism or natural forces with only a fraction of offspring surviving each generation This is called the struggle for existence

Members of a species show variation.

Sexual reproduction promotes variation in a species.

Meiosis: Crossing over of homologous chromosomes during prophase I results in a recombination of maternal and paternal alleles within chromosomes Independent assortment as homologous chromosomes randomly orient at metaphase I causing a randomized inheritance of maternal and paternal chromosomes within gametes

Fertilization: New combinations of alleles appear during fertilization As the unique set of haploid alleles in the egg Combine with the unique set of haploid alleles in the sperm

• Independent Assortment Crossing Over

Natural selection

Those individuals whose inherited characteristics(variations) best fit them to their environment are likely to leave more offspring than less-fit individuals A fish with a better shaped mouth might be able to feed on coral that cannot be accessed by other fish, he will have a better chance of survival into adulthoodA fish mouth could be inadequately adapted and as a result die of starvation

Natural selection

This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with the inheritance of favorable characteristics accumulating over the generations.

5.4.8 - Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria

Antibiotic resistance in bacteria• Shortly after development of antibiotics (e.g.

penicillin) nearly all bacteria were killed during an application. Only those who had a gene for antibiotic resistance survived to reproduce.( 1 resistant bacterium can produce 10000000000 descendants in 24 hours under favourable conditions!)

• Repeated applications of antibiotics produced, over time, a greater proportion of individuals with resistance to the antibiotics

• Antibiotics resistance is the variation that is selected for

Evolution

Peppered moths

Industrial melanismDuring the day the moth rests underneath the branches of trees and relies on camouflage to protect it from insect-eating birds

Speckled form

Black form

Until 1849 only the speckled variety was observed. From 1849 (industrial pollution getting worse) until the late 1960’s the black variety was reported in ever-increasing numbers

A single gene controls appearance. The alleles are - C: black, c: speckled

Trees in unpolluted regions often had growths of speckled lichen. This lichen was killed off in polluted areas, causing bark to look much blacker

Selection pressure: Bird predation? Successful allele? Black form has more chance of survival in polluted areas.

General biocide resistance in insects •Shortly after development of biocides (e.g. DDT) nearly all insects were killed during an application except those with a variation that helped to resist the insecticide.These survived to reproduce, passing on the gene to next generation. •Repeated applications of biocides produced, over time, a greater proportion of individuals with resistance to the biocide •Biocide resistance selected for

Outline two modern examples where evolution can be observed. 2 marks

•Change of beak shape in Galapagos finches •Resistance to pesticides/antibiotics •Bird predation on moths •Heavy metal tolerance in plants

Outline five types of evidence which support the theory of evolution by natural selection. 6 marks

•Geographic distribution: ring species/other evidence from geographical distribution •Biochemistry: cytochrome c/other biochemical evidence •Fossils/paleontological: fossilized horse ancestors/other evidence •Homologous structures: pentadactyl limb •Resistance to antibiotics/insecticides/heavy metal tolerance.

Explain the evidence from homologous anatomical structures that supports the theory of evolution. 6 marks

•Homologous structures are various different structures of the same basic plan derived from a similar embryonic origin •Variations on the basic structure allow different functions permitting exploitation of different ways of life/adaptive radiation •This suggests divergence from a common ancestor •Example of a homologous structure is pentadactyl limb of mammals •Basic structure of this is the same in a horse, humans, bats and whales. Humerus, radius, ulna, carpals, meta carpals and phalanges are there in all. •variation in the structure is related to different functions of this organ in these individuals