Evolutionary Processes 1
Alleles
Different versions of the same gene. Created by random mutations.
Natural Selection
Increase in frequency of alleles that code for fitter traits in a population over time AND decrease in frequency of alleles that code for less fit traits.
Species
Organisms that can interbreed together and produce fertile offspring
Speciation
The process of a population splitting into two or more sub-populations that become reproductively isolated then accumulate genetic differences that prevent them from interbreeding over time.
Diploid
Cells that have two copies of every chromosome (2n). This is the default for most sexually reproducing species somatic cells.
Haploid
Cells that contain only one of each chromosome (1n). This is the default for gamete cells in sexually reproducing organisms.
Transitional Fossils
A series of fossils that show gradual change in anatomy from an ancestor to modern day (extant) species
Divergent Evolution
When a population is split into two sub-populations that experience different selection pressures and evolve into two or more species over time.
EVIDENCE:
- homologous structures
- high % DNA similarity
- close together on phylogenetic tree
- mtDNA clock shows recent shared ancestry
- transitional fossils
Gene Flow
Movement of alleles between gene pools, this keeps populations the same and stops them from speciating.
Directional Selection
Type of natural selection where one extreme version of a trait gets selected for over time eg. antibiotic resistance in bacteria
Pre-zygotic RIM
Reproductive Isolation Mechanisms that occur before fertilization eg. behavioural, ecological, geographical, mechanical, gamete incompatibility.
Allopatric Speciation
Speciation that is started when a population is split into two+ geographically isolated sub-populations eg. by a mountain range, glacier forming, river valley, continental drift.
Meiosis
The process of making gametes that contain HALF the amount of genetic material as the parent cells they came from eg. 2n --> 1n
Autopolyploidy
Polyploids that form within the same species eg. when a plant makes 2n pollen that fertilizes a 1n ovule of the same species, making a 3n triploid.
% DNA Similarity
The amount of shared DNA base pairs between two living species. The higher the number the more closely related they are and the more recently they diverged from a common ancestor.
Adaptive Radiation
When one ancestral population diverges into many species very quickly. This occurs when there are many empty niches to fill (eg. after a large natural disaster) or when competition is very intense (eg. on a small island).
Genetic Drift
Stabilising Selection
Type of natural selection where the middle/average version of a trait is selected for over time and the two extremes are selected against eg. human head size
Post-zygotic RIM
Reproductive Isolation Mechanisms that occur after fertilization eg. Hybrid inviability, Hybrid infertility, Hybrid breakdown.
Sympatric Speciation
Speciation that is started when a population is split into two+ reproductively isolated sub-populations but this is NOT geographical eg. a mutation causes a behavioural change, mechanical change, gamete incompatibility.
Gametes
Cells used for sexual reproduction these contain half the amount of genetic material of the parent that produced them eg. 2n --> 1n
eg. sperm, eggs, pollen, ovules
Allopolyploidy
Polyploids that form when two species interbreed and form a hybrid. This hybrid is sterile as it doesn't contain homologous pairs of chromosomes even if it's 2n.
Phylogenetic Tree
A tree showing how closely or distantly related two or more species are. Species that cluster together on the tree are closely related.
Homologous Features/Traits
This indicates recent shared ancestry and divergent evolution.
Bottleneck
A sudden and large decrease in population size that leads to the random loss or fixation of an allele even after the population recovers.
Disruptive Selection
Type of natural selection where the middle/average phenotype is selected against and the two extremes are selected for eg. rock pocket mice coat colour (black and tan).
Hybrid Inviability
When two species mate and produce an offspring but the offspring dies before reaching maturity.
Deme
Two or more sub-populations that are partially reproductively isolated but can still interbreed with each other.
Triploid
Cells that contain 3 copies of every chromsome (3n). If this is in somatic cells they will be infertile and unable to make gametes.
Homologous Chromosomes
Pairs of chromosomes that have the same genes in the same locations on them.
mtDNA Clock
Mitochondrial DNA clock; DNA from mitochondria are passed down clonally from mother to offspring so the DNA only changes due to a constant steady muattion rate. This rate can be used to decide how long ago two living species diverged from a common ancestor.
Co-Evolution
When two closely interacting species put reciprocal selective pressure on each other eg. a pollinating bat's tongue length randomly increases, this puts a pressure on flowering plants so their flower tubes increase in length
Founders Event
A small non-representative sub-sample of a large gene pool creates a new isolated population with less genetic diversity than the original population it came from.
Selection Pressure
Anything in the environment that sorts organsisms into fit versus non fit varieties eg. predators, drought, disease, cold temperatures.
Hybrid Breakdown
When two species mate, make an offspring, and that offspring is fertile, but the F2 generation is infertile.
Cline
A gradual change in phenotype over a geographical gradient due to gradually changing selection pressures. Neighbouring sub-populations can still interbreed.
Chromosome Nondisjunction
When spindle fibers fail to separate pairs of chromosomes during meiosis, leading to polyploid gametes.
Chromosome Doubling
When an organism duplicates all of its chromosomes. This makes an allopolyploid fertile since it will now have homologous pairs of chromosomes.
eg. ABCD --> AABBCCDD
Analogous Features/Traits
Anatomical features that are used for the same function/purpose but have very different underlying structures eg. insect wings and bird wings. This indicates convergent evolution rather than recent shared common ancestry.
Punctuated Equilibrium