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AQA Tags Archives: Investigating diversit

Species and taxonomy

Genetic information, variation and relationships between organisms (AQA AS Biology) PART 4 of 6 TOPICS

 

 

TOPICS: DNA, genes and chromosomes  Genetic diversity can arise as a result of mutation or meiosis  Genetic diversity and adaptation  Species and taxonomy  Biodiversity within a community  Investigating diversity

 

 

Species and taxonomy:

Two organisms belong to the same species if they can produce fertile offspring.

Physical and chemical makeup help distinguish members of species. Behaviours also does this too where most behaviours are genetically determined. Courtship and mating are essential when it comes to survival. Recognition of members helps to produce fertile offspring with a mate who is capable of breeding, strong and healthy as well. Whilst doing this aggression should not be triggered. Courtship can be:

  • Visual: Using colours
  • Behaviour: Dances or building nests
  • Pheromones: Chemicals released by an organism enabling it to communicate with other members of its own species.

Phylogeny is a classification system which attempts to arrange species according to their evolutionary origins and relationships. It uses a hierarchy in which smaller groups are placed into larger groups. These groups are known as taxa and they do not overlap.

The taxons are: Domain, Kingdom, Phylum, Class, Order, Family, Genus and Species.

Each species is universally identified by a binomial consisting of the name of its genus first then the species.

NB: The 3 types of domain and the 5 types of kingdom do not need to be recalled for the AQA exam.

 

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Genetic diversity and adaptation

Genetic information, variation and relationships between organisms (AQA AS Biology) PART 3 of 6 TOPICS

 

 

TOPICS: DNA, genes and chromosomes  Genetic diversity can arise as a result of mutation or meiosis  Genetic diversity and adaptation  Species and taxonomy  Biodiversity within a community  Investigating diversity

 

 

 

Genetic diversity and adaptation:

As the number of alleles increases so does genetic diversity in a population.

Genetic diversity allows natural selection to occur.

Evolution is a change in a populations’ alleles and genotypes from generations to generations. Therefore it should be considered at a population level. Five factors affect the proportion of homozygote and heterozygote:

  • Genetic drift: This is a change in the gene pool that occurs in a small population due to chance. Two situations can lead to genetic drift:
  • Population Bottlenecks: This is when a large number of a population is wiped out due to disease, natural disasters or overhunting
  • Founder Effect: This is when a new colony is found by a small number of individuals
  • Gene flow: This is the movement of alleles from one population to another when a member moves into another population. The variety of alleles that this member has can significantly affect the gene pool of a population especially if it has good survival and mating skills.
  • Mutations: These are changes to an organisms DNA. The change is transferred to gametes which immediately changes the gene pool. This is a rare event but the cumulative effect is massive. Mutations themselves play an insignificant role in changing the frequency of alleles in a population.
  • Non-random mating: Homozygous individuals increases when preferred organisms mate with each other, causing frequency of genotypes to differ significantly from equilibrium values. Populations consist of individuals with different genetic make-ups. This means that Hardy-Weinberg equilibrium is not maintained. NB: Hardy-Weinberg equilibrium equation and definition does not need to be known for AS only for A2.
  • Natural selection: Populations consist of individuals with different genetic make-ups. Colourful and vibrant organisms are more susceptible to predation.

Directional selection happens in bacteria for example, where the bacteria are resistant to antibiotics leading to an increase in the frequency of the allele that is resistant to antibiotics.

Stabilising selection happens in an changing environment. Stabilising selection occurs in the natural selection of birth mass in humans. Extremes of the phenotype range are selected leading to a reduction in variation.

 

The thin blue line shows the distribution of mass at birth of children born in University College Hospital over a 12-year period. The thick blue line shows the percentage prenatal mortality (those failing to survive four weeks) on a logarithmic scale. ‘O’ shows the optimal mass that had the lowest prenatal mortality. ‘M’ is the mean birth mass.

 

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