20.6 Spciation And Artificial Selection

Question 1

Define speciation

Answer 1

The formation of new species through the process of evolution

The organism belonging to the new species will no longer be able to interbreed to produce a fertile offspring with organisms belonging to the original species

Question 2

Events that lead to speciation

Answer 2

• members of a population become isolated and no longer interbreed with the rest of the population resulting in no gene flow between the two groups
• alleles within the groups continue to undergo random mutations. The environment of each groups may be different or change (resulting in different selection pressures) so different characteristics are selected for and against
• the accumulation of mutations and changes in allele frequencies over many generations lead to large changes in phenotype
  The member of the different population become so different that they are no longer able to interbreed (to produce fertile offspring). They are now reproductively isolated and are different species

Question 3

Describe and explain allopatric speciation

Answer 3

Happens when some members of a population are separated from the rest of the group by a physical barrier (e.g. river or the sea) and are geographically isolated

The environments of the different groups will often be different so will the selection pressures resulting in different physical adaptations
- will often result in founder effect leading to genetic drift further enhancing differences between the he populations

Question 4

Describe and explain sympatric speciation

Answer 4

Occurs within populations that share the same habitat
(Not as common as allopatric speciation)
More common in plants than in animals

• it can occur when members of two different species interbreed and form fertile offspring - often happens in plants
  This reproductively isolates the hybrid organisms
  E.g. fungus-farming ants

Question 5

Describe and explain artificial selection

Answer 5

Artificial selection (or selective breeding) is where humans choose the plants and animals with desired characteristics to breed

The breeder of closely related individuals is called inbreeding. Process is repeated over many generations resulting in changes to the frequency of alleles within the population and eventually speciation

Question 6

Problems caused by inbreeding

Answer 6

• gene pool reduced, so genetic variation decreases
• genetic disorders become more common (number of homozygous recessive increases and most genetic disorders are caused by this genotype)