Evolution and Biodiversity - Edexcel GCE Biology Revision Notes

by kinyung102902hotmailcom (student)

AS and A Level Science

Variation

Individuals of the same species have different genotypes (different combination of alleles) This results in a variation in phonotype (the characteristics displayed by an organism)

Some characteristics are monogenic - they can only be controlled by one gene (shows discontinuous variations). Whereas most characteristics are controlled by a number of genes at different loci / locus (position on chromosomes), these are said to be polygenic and would usually show continuous variation.

Although some characteristic are only influenced by genotype (i.e. Blood group), most characteristic are influenced by both the genotype and the environment (i.e. Weight).

Height is polygenic and affected by environmental factors, especially nutrition. I.e. Tall parents would have tall children, however, f the children are undernourished they will not grow to their maximum height (because lack of protein means stunted growth)

Monoamine Oxidase A (MAOA) is an enzyme which breaks down monoamine (a type of chemical) in humans. Low levels of MAOA have been linked to mental health problem. NAOA production is monogenic, however taking anti depressants or smoking tobacco can reduce the amount produced.

Cancer is the uncontrolled division of cells that leads to lumps of cells (tumours) forming. The risk of developing some cancer is affected by genes; however environmental factors such as diet (i.e. Smoking) could influence the risk.

Animal hair colour is polygenic, though it can also be influenced by the environment. I.e. Some arctic animal have dark hair in summer but white hair in winter. Environmental factors such as decrease in temperature would trigger this change, but it cannot happen if the anima didn’t have the genes that enable this change.

Data on variations are difficult to interpret as some characteristics are controlled/ influenced by many different gene (if polygenic) and environmental factors.

Therefore it’d be hard to know which factors (gene or environment) are having the greatest effect - making it hard to draw conclusions about the cause of variation.

Adaption and Evolution

A niche describes the position & function of a species with its ecosystem, including:

- Its habitat so the place where it lives, i.e. A woodland or a hedgerow

- It’s interaction with other organisms, for example the organisms it eats and those it is eaten by (prey and predator)

- Its interaction with the non-living environment, i.e. the oxygen an organism breathes in and the carbon dioxide it breathes out.

Every species has its own unique niche (as a niche can only be occupied by one species). If 2 species attempt to occupy the same niches, they will compete with each other until one is left (as one will be more successful)

Although it may seem as if two species are occupying the same niche, but sometime there are slight differences (what food they eat, who preys on them etc.)

Adaptations are features that increase an organism’s chance of survival and reproduction. All species have adaptation that allow them to use their environment in a way that no other species can - they’re adapted for their niche, this includes:

- Behavioural adaptation is ways an organism acts for better chance of survival and reproduction. I.e. animal makes mating calls to attract female.

- Physiological adaptations is processes inside an organism’s body that increase its chance of survival. Some organisms lower their metabolism in order to hibernate over winter - allowing them to conserve energy when food is scarce.

Anatomical adaptations are structural features of an organism’s body tht increases its chance of survival, i.e. some bats have light, flexible wings that allow them to hunt fast-flying insects

Advantageous adaptations become more common in population of species because of evolution by natural selection.

Individuals within a population show variation in their phenotypes, predation, disease and competition created a struggle for survival.

- Therefore, individuals with better adaptations are more likely to survive, reproduce and pass on their advantageous adaptation to their offspring.

- Overtime, the number of individual with the advantageous adaptation increase and over generations, this would lead to evolution as the favourable adaptation become more common in the population.

That was the Charles Darwin’s theory of evolution by natural selection. This theory becomes increasingly accepted as more evidence has been found to support it and none shown to disprove it. Evidence increases scientist’s confidence in a theory - the more evidence, the more a theory becomes an accepted scientific explanation.

Peppered moths show variation in colour - light and dark ones. Before the 1800s there were more light moths than dark moths.

During the 1800s, pollutions have blackened many of the trees that the moths lived on. Dark coloured moths were now better adapted to this environment as they were better camouflaged from predator - therefore would be more likely to survive, reproduce and pas on their dark colouring to their offspring.

Therefore during this time, the number of dark moths increased.