Key Area 7 - Evolution Flashcards
Evolution Definition
Evolution is the changes in organisms over generations as a result of variations in the genome.
Natural Selection Definition
Natural selection is the non-random increase in frequency of DNA sequences that increase survival and the non-random decrease in frequency of deleterious sequences.
Gene Transfer
Natural Selection is more rapid in prokaryotes.
Prokaryotes can transfer genetic information horizontally. This results in faster evolutionary change compared to other organisms.
Non-prokaryotes transfer genetic material vertically which is a slower process.
Horizontal Gene Transfer
Horizontal gene transfer is where genes are transferred between individuals in the same generation. This does not occur due to reproduction.
Vertical Gene Transfer
Vertical gene transfer is where genes are transferred down generations, from parent to offspring.
This can happen through sexual and asexual reproduction.
Sexual Reproduction
Sexual reproduction involves two genetically different parents.
Offspring inherit different combinations of genes from each parent causing variation.
Asexual Reproduction
Asexual reproduction involves one single parent.
Offspring produced are genetically identical to the parent.
Selection:
Stabilising
An average phenotype is selected for and extremes of the phenotype rage are selected against.
E.g human birth mass
Selection:
Directional
One extreme of the phenotype range is selected for.
E.g bear mass during an ice age
Selection:
Disruptive
Two or more extreme phenotypes are selected for.
E.g dark and light mussels
Speciation Definition
Speciation is the generation of a new biological species by evolution.
Stages of Speciation
- Isolation
- Mutations occur randomly across the sub-populations
- Different selection pressures act on both sub-populations
Isolation Barriers
A population is split into sub-populations by an isolation barrier
Isolation barriers prevent gene flow between the sub-populations.
Isolation barries can be:
* Geographical: This leads to allopatric speciation
* Ecological: This leads to sympatric speciations
* Behavioural: This leads to sympatric speciation
Species Definition
A species is a group of organisms that are capable of interbreeding and producing fertile offspring, and which does not normally breed with other groups.
