Natural Selection and Evolution

Allele

Alternative form of gene

Mutation

A permanent change in genetic material

Mutagens

Substances that increase the chance of mutations to occur. There are three types- biological, chemical and physical

Biological

Bacteria and viruses- HPV

Chemical

Mustard Gas

Physical

UV rays

Insertion

One nitrogen base is inserted into gene sequence which makes the gene longer creating a large scale movement called a ‘frame shift’. This affects the amino acids due to triplet and codon combinations being affected and protein that is produced

Deletion

Nitrogen base/s is removed from sequence making gene shorted affecting amino acids formed therefore affecting the protein that is produced. The gene is shorter as a result of deletion.

Substitution

Single base is swapped for another and may/may not affect the amino acid and protein that is produced. Gene length remains the same.

Frameshift

Shift of reading frame of triplets/codons

Fossils

Preserved traces in soil that remain undisturbed over a long time usually forming sedimentary rock over a long time. For example, fossils can be preserved traces of bone and teeth.

Conditions

Rapid burial, soil depleted of oxygen and water (as decomposers such as bacteria thrive in moist environments), alkeline soil (otherwise acidity would dissolve bones), hard body parts (teeth, bone), time

Fossils as evidence of evolution

Evolutionary links established between species/common ancestry.

Evidence of which organisms lived on Earth a long time ago

Examples of organisms which may not be extinct

Examples of transitional organisms between species

Superposition

The youngest layers are near the surface and the oldest layers are the deepest

Strata

Layers of rock

Index fossils

Fossils that are found over a large geographical range, distinctive, only present for one layer in each outcrop (short time period) and have a known age range.

Comparative antanomy

The comparison of structures in organisms in both fossils and species

Homologous structures

Common structures that organisms in different species that often have a similar pattern but differnt function. For example, pendactyl limb- a pattern of limb bones in a group of tetrapods

Homologous structures as evidence for evolution

• All verterbrates must be descended from a common ancestor

• Bone structures are similar but have been slightly modified to suit a particular function. Species were exposed to different selective pressures

Vestigial organ

An organ that is present in modern animals but are no longer functional. This suggests that a common ancestor once had a use for structure such as an appendix- as our diet has changed, so there has been a change in selective pressures.

Vestigal organ as evidence for evolution

Pelvis is used for distributing weight from upper body to the lower limbs when walking. Whales no longer walk/weight bear through their legs, so the pelvis is no longer functional. This suggests that whales have descended from an ancestor that walked on land.

Comparative embryology

The comparison of development, structure and function of embryos from different species. For example, fish, lizards, rabbits and human embryos have spinal gills

Comparative embryology as evidence for evolution

Number of common structures for all embryos- spinal cords, limb buds, gills, tail that are coded for genes. This suggests that these organisms must have inherited these genes from a shared ancestor.

Genome

The complete DNA sequence of an organism found in every cell

Comparative genomics as evidence of evolution

Compare genes of organisms looking for differences in base order. The more similar the DNA between organisms of different species, the more closely related the species are/the more recent the common ancestor is

Comparative proteins

Proteins are long chains of amino acids. The sequence of amino acids is determined by the sequence of bases in DNA.

Comparative proteins as evidence of evolution

Comparing type and sequence of amino acids from different species, degree of similarity can be established. Fewer differences in the amino acid sequence indicates that there is a more recent ancestor/ more closely related. Less time for mutations to accumulate in DNA.

Phenotype

Physical makeup off organisms determined by the organisms genes and its environment.

VISS (8 marks)

Variation- state and type Isolation- Isolation factor and Prevents Interbreeding Selection- Different selective pressures, what survived and reproduced x2, difference between populations increase/accumulate over time Speciation has occured.

VST (5 marks)

State variation and type, identify selective pressure, favoured trait and why, disadvantaged trait and why. Over time individuals with the favoured trait are bred more frequently. Over time allele frequency of the favoured trait increases within the population due to selective breeding.

VOSSR (8 marks)

state variation and type, competition for resources/survival in population. identify selection pressure, favoured trait and why, disadvantaged trait and why, favoured trait individuals survive and reach maturity, individuals with the disadvantaged trait are less likely to survive. individuals reproduce, passing on the favored allele _.Over time the frequency of the favored allele _____ increases within the population.