D4.1 Natural Selection

Four requirements for Natural Selection

• Overproduction of offspring

• Variation

• Survival of the fittest

• Advantageous traits become more frequent

Mutation

Creation of new alleles

Meiosis

Creation of new combination of alleles

Sexual reproduction

Fertilisation of gametes

Overproduction

More offspring are produced than can be supported by environment

Abiotic factor

Non-living factor

Examples of density-independent abiotic factors

• Freezing or hot temperatures

• Natural disasters

  • Salinity

Density dependent factors

• Soil mineral availability

  • Access to water

• Predation

Fitness

Degree to which genetic components give an advantage to an organism

Acquired traits

Traits that can help an individual, but will not be passed down to offspring

Sexual selection

Identifying and choosing potential mates that are best adapted and likely to produce offspring that are also well adapted

Gene pool

All different genes and alleles in a population

Genetic equilibrium

All individuals in a population have an equal chance of contributing to gene pool

Natural selection involves:

giving individuals an advantage, making it more likely that they contribute to the gene pool and disrupting genetic equilibrium

Neo-Darwinism

Integration of understandings of natural selection and genetics

Allele frequency

Proportion of an allele in a gene pool

Evolution

Change in allele frequencies in gene pool

Stabilising selection

Average phenotypes having an advantage over extreme phenotypes

Disruptive selection

Extreme phenotypes having an advantage over average phenotypes

Directional

One extreme phenotype has an advantage over the other

Hardy-Weinberg equation + meanings

• p² + 2pq + q² = 1

  • p²→ frequency of homozygous dominant genotype (BB)

  • 2pq → frequency of the heterozygous genotype (Bb)

  • q² → homozygous recessive genotype (bb)

  • p → frequency of the dominant allele (B)

    • q →frequency of the recessive allele (b)

Difference between natural selection and artificial selection

Natural selection	Artificial selection
Environmental pressures control reproduction	Human control reproduction