Speciation and artificial selection

• Speciation = formation of a new species through evolution
• New species will not be able to interbreed with old species to produce fertile offspring

Allopatric speciation

• More common form of speciation for animals
• Some members of a population are geographically isolated from original group 
• The environments will be different for each group
• Selection pressures for either group result in different physical adaptations
• Smaller group will result in founder effect, leading to genetic drift which further enhances their differences to the original group
• Eventually the mutations will accumulate in both populations until they're so different that the are no longer able to successfully interbreed --> reproductively isolated and are different species
• Darwin's finches!
• ^ adapted in different environments with different food sources so they became suited to these food sources

Sympatric speciation

• Occurs within populations that share the same habitat
• More common for plants
• It can occur when two different species interbreed to form fertile offspring
• The hybrid formed is a new species as it will have a different number of chromosomes to its parents and may no longer be able to interbreed with either parent population 
• This stops gene flow and reproductively isolates the hybrid
• Disruptive selection, mating preferences and other behavioural differences can result in individuals or groups becoming reproductively isolated

Artificial selection or selective breeding

• Populations are usually polymorphic (display more than one distinct phenotype)
• The allele coding for the most common characteristic is the wild type allele
• Mutants = other forms of that allele resulting from mutations
• Artificial selection is basically the same as natural selection except the selection pressures are different
• Instead of changes in the environment, its the desirable traits which provide the selection pressures
• Individuals with desirable traits are selected and interbred by farmers
• Offspring of this cross showing the best examples of the desired traits are selected and bred again
• This process repeated over and over changes the frequencies of alleles within the population and will eventually lead to speciation

Problems caused by inbreeding

• Limiting the gene pool reduces the genetic variation which reduces the chances of evolution and adaptations
• Many genetic disorders are caused by recessive alleles
• When organisms are interbred, the frequency of these recessive genes can increase meaning there's more chance of offspring having the genetic disorder
• Over time, this reduces the ability of the organisms to survive and reproduce

Gene banks

• Seed banks keep seeds from both wild and domesticated varieties of plants
• Gene banks store biological samples (sperm and eggs)
• Alleles from gene banks are used to increase genetic diversity in a process called outbreeding
• Breeding unrelated or distantly related varieties is also outbreeding
• Reduces the occurance of homozygous recessive and increases the potential for the population to adapt and evolve