Genes Evolution & Development L4 Flashcards
What is the biological definition of a species?
Population of reproducing organisms that is isolated from other populations.
Various ways/forms in which species can arise?
- Over time along ancestral lineage
- Across locations -> geographic isolation
- Variety of genetic effects
Identified by comparison of populations -> population genetics.
These processes can be observed.
What is the controversy amongst scientists surrounding the definition of species?
- (Biological definition) -> Population of reproducing organisms that is isolated from other populations.
However:
Prokaryotes & eukaryotes -> not strictly sexual Eg. plants.
Doesn’t consider extinct organisms
Bacteria & archaea -> horizontal gene transfer. - Definition is widely debated/ discussed among scientists. -> each bases on their own field of interest.
What is a species?
- Group of individuals with similar characteristics & DNA sequences, sharing common ancestors, which can reproduce to produce fertile offspring.
What is speciation? Outline the process of speciation.
- The evolutionary process in which new, distinct species evolve from an existing population due to reproductive isolation.
- Population divides -> populations become isolated from one another -> selection pressures, adaptations, changes in characteristics, mutations -> do not recognise when reintroduced.
Population becomes reproductively isolated following start of speciation due to
Selective pressures
Genetic Drift
Genetic mutations
Of each individual population. - Consequential event of specific conditions, involving by-products of subsequent selection.
- Occurs over long time periods -> selection not involved.
Types of speciation?
- Allopatric
- Sympatric
- Paraphatic
Describe allopatric speciation with an example
- Allopatric speciation:
(Allos = other; patra =homeland) -> Classic, widespread.
Geographical isolation of existing population
Eg. Antelope Squirrels -> Grand Canyon. -> Birds on both sides show no such effects/speciation.
Describe sympatric speciation with an example.
- Sympatric speciation:
(Sym = same ; patra = homeland) -> Theoretically debated -> animals -> few examples
-> Commonly found in plants
No geographical isolation of groups.
Eg. Change in behaviour -> nocturnalism of one group
-> natural selecton -> use of different resources
Eg. Shortcleuch Waters –(see also allypolyploid evolution below)
What is paraphatic speciation?
Somewhat but not complete geographical isolation -> reproductive barriers when restricted gene flow.
Average length of speciation event?
(Mean time: Single eukaryotic population -> Two reproductively isolated populations
> Up to 5,000,000 years.
• Different types of selection?
- Directional selection -> population tends in direction of one characteristic
- Disruptive Selection -> range is separated to two extremes
- Stabilizing selection -> focused population around mean
• What is genetic drift?
Give examples of how it could occur.
• What is genetic drift?
Substantial change in genetic variation due to the chance disappearance of particular genes of a population, without regarding advantageous values of characteristics involved.
Eg. 1. Bird -> alleles for two different beak sizes -> by chance offspring may inherit only one particular beak size -> one allele disappears & genetic variation reduced.
Eg. 2. Certain plant -> alleles for blue & yellow flowers -> during a fire, many yellow flowers destroyed -> blue flowers are now dominant by chance -> reproduce more blue than yellow -> eventual disappearance of yellow altogether as reproduction rate not as high.
Name the types of genetic drift.
- Bottleneck
2. Founder Effect .
What is a bottleneck?
Bottleneck -> Random event -> loss of certain characteristics/alleles -> decreases range of allele frequency.
What is the founder effect?
.Founder Effect -> New population started by few members of original population -> decreased genetic variation.
Describe the effect of different sized populations.
- > Small population -> leads to substantial genetic differences.
- > Large randomly mating pop -> Unlikely for large fluctuations in gene pool variety.
- > Small pop -> random effects -> major changes without influence of selective process.
Why does genetic drift occur?
No intention/purpose – pure chance - just because of statistics of small population.
Two examples of speciation?
- Blackcap
Breeds -> Central Europe
Winter -> Spain (& UK for last 30yrs)
Assortative mating -> Strong signs of genetic & morphological differences across Spanish & UK populations
• Varied arrival time at breeding grounds -> rapid genetic change. - Hooded & Carrion crows:
Distribution: -> split down the middle of Europe (carrion->west ; hooded->east)
Different colour patterns -> mate with others of similar pattern & different dominance behaviour.
Appear distinct species but have extremely similar genetic sequences.
Some fertile hybrids.
Found 83 fixed differences in genetic sequence -> 81 occurring on a small region of single chromosome -> chromosome 16.
Transcription factors -> pigmentation & vision.
Likely contained in an inversion -> free genetic interchange of chromosomes except in F-K region -> cross over in this region -> inviable zygotes.
• Inversion keeps genes together -> pigment & preference for associated pigment -> stable system.
What is an inversion?
Breakage & backward insertion of part of a chromosome back into the full chromosome.
Name the genetic factors in speciation.
- Genetic Drift & Bottlenecks -> long periods of isolation
- Natural selection
Describe the process of reinforcement as a role of selection/Role of selection in divergence after selection.
Two populations have divided enough -> unfit hybrids
Natural selection prevents formation -> strengthens reproductive isolation & difference in species through reinforcement.
Individuals who can avoid unproductive matings (infertile offspring) -> advantageous
> If mating does result in fertile hybrids -> hybrid breakdown at/after F2.
Natural selection directly favours evolution of species a s distinct groups.
What are hybrid zones?
List the possible outcomes of a hybrid zone.
- Areas in which hybrids are made as a result of sympatric speciation & reinforcement by selection can be observed.
1. Fusion
2. Reinforcement of isolation
3. Stability
Describe how fusion occurs as a result of a hybrid zone.
- Inter-fertile -> Lots of gene flow between populations = fusion of two groups.
Describe how reinforcement of isolation occurs as a result of a hybrid zone.
- Some gene flow -> significant loss of fitness in hybrids = reinforcement of isolation.
Describe how stability occurs as a result of a hybrid zone.
- Limited gene flow -> few hybrids -> negligible loss of fitness = stability
Explain the process of polypoloid speciation with an example.
(Allypolyploid evolution)
• Occurs in plants -> incr. genetic, physiological & developmental flexibility.
1. Plant doubles it’s number of chromosomes due error in formation of gametes. -> Can no longer reproduce with others of it’s species.
2. Therefore reproduces with itself to produce a new species.
Eg. M. guttatus -> 14 pairs chromosomes ;
M. luteus -> 30/31 pairs
-> Interbreeding produces triploid hybrids -> 3 copies of each chromosome pair. -> Sterile – Can’t produce fertile offspring.
M. peregrinus -> six copies of each chromosome pair -> evolved from duplication event in infertile offspring.
Can produce normal haploid gametes with 46 chromosomes – x4 guttatus.
Are inter-fertile & isolated from other closely related species.
