Natural selection stuff Flashcards
What are the examples that cause variation.
Mutations
Non dysjunction
random assortment
random fertilisation
crossing over
Describe Genetic Drift
Random genetic drift is a random, non directional fluctuations in allele frequency. ( not due to evolution)
Occurs in small populations
Occurs due to random mating/ random events
Occurs when variant forms of a gene (alleles) increase or decrease by chance over time. This changes the allele frequencies over time.
LOOK OUT FOR WORDS LIKE SMALL, CHANCE EVENT and “ RANDOM” ——-> CAUSING THE CHANGE IN FREQUENCY.
ALSO LOOK OUT FOR HIGH FREQUENCY—> non- adaptive trait.
Describe bottle neck
A subheading of Random genetic Drift
sudden drop in population size
-Natural disasters
-Wars
-migration
Genetic bottle neck effect-> result of inbreeding brought by limited mating possibliites-> amplify certain traits, however greatly increase risk of of unusual, harmful traits being epressed.
Analyse Founder effect
Small number of people migrate away from their home land-> to new area to establish new community.
Reproduction occurs
Small group of original population does not genetically representative of the original population. New community usually doesn’t show feautre typical with the original population
Ouline Natural Selection in detail.
Variation-> Sources of Variation
Mutations ->
Non dysjunction->
Random assortment->
Random fertilization->
Crossiver over->
Change in Gene flow->
Overproduction-> each species produces more offspring thqt can survive.
Struggle of existence-> high birth rate and limited resources, thus struggle for existence, individuals in a population may fight for resource thus reduce likelihood of living.
Selective agents is a enviromental factor that can act upon the population
Survival of the fittest-> Those individuals that are best adapted
to their enviroment are more likely to survive ( favourable trait) the ones with less favourable traits are least likely to reach repro age.
Thus more likeyl to reach reproductive age
Allele crossing over-> individuals with the fav. allele reach reproductive age and pass on allele to offspring.
Change to gene frequency- over time (as more generations also have fav allele) the fav allele frequency (%) is maintained or increases in gene pool.
Barries to gene flow
Barriers seperate populations inhibiting interbreeding and geneflow.
Barriers= isolation-> results in seperate gene pools and can even lead to speciation.
For i.e
Geographical-> ( oceans, mountains, desert)
Socio-cultural-> ( religion, language, social position , education, economic factors)
Describe Speciation and the steps
If two populations are seperated for a long enough time period and the enviromental influences ( selective agents) are different enough, major changes in the allele frequencies within each population would occur.
to a point where if barrier is removed, interbreeding would no longer be possible ( thus new species form)
- Variation-> range of variations exist within a population sharing a common gene pool
- Isolation-> An enviromental barrier ( geographical, sociocultural)-> prevents geneflow, no interbreeding can occur each population has a seperate gene pool.
- Selection-> Different selection pressures exerted on each population. Change in gene frequencies occurs due to natural selection.
Evolution of a separate subspecies occurs.
- Speciation->Over long periods of time gene frequencies are so different that interbreeding will no result in fertile offspring.
Two new species are formed.
Compare Large populations and Small populations
Large populations->
Allele frequency are more stable and reflect natural selection ( higher frequency of better suited alleles)
Higher population thus individuals make only small contribution to gene pool-> The number of alleles tend to stay the same= stable.
EVolution= slow
Changes= adaptive
Small population->
Allele frequency is less stable
Indivduals make a larger contribution to the gene pool-> the Number of alleles tend to fluctuate.
Evolution= fast
Changes= non adaptive and random
Random drift is evident.
Natural selection ( sickle cell anaemia)
Variation exists in the gene pool. Different patterns of inheritance for RBC shape.
- Sickle cell anaemia is caused by a point mutation (a substitution gene mutation) which disrupts the normal Hb production = RBCs are sickle shape.
Overproduction & Struggle for existence:
- In geographical areas where Malaria is present – the selective agent is Malaria disease & puts ‘pressure’ on the populations that live in these areas. Not all will survive
Survival of the fittest / Selection
- Individuals who are Heterozygous normal (HbAHSS) have some normal RBCs and some sickle shape RBCs = they have the survival/Heterozygous advantage = they have increased resistance to Malaria = therefore more likely to survive.
- Homozygous for SCA (HbSHbS) despite resistance to malaria = typically die/do not reach repro age due to sickled RBCs = have low O2 carrying capacity, sickled RBCs can block vessels = experience ill effects associated with this disease.
- Homozygous normal (HbAHbA) have normal shaped RBCs, despite normal O2 carrying capacity they have no resistance to malaria – thus more susceptible to die due to the malaria disease
Allele carryover:
- As Heterozygotes survive due to resistance from malaria, they reach reproductive age and the Sickle cell allele (HbS) is passed on to future offspring & future generations (over time).
Gene Freq. changes:
- In areas where Malaria – because SC allele has been passed on the SC allele frequency is maintained or still persists within the gene pool
Population
a group of organisms of the same species living together in a particular place at a particular time
Species
a group of individuals that share many characteristicsand are able to interbreed under natural conditions to produce fertile offsprings
Gene pool
a sum of all alleles in a given population
Allele frequency
how often each allele of a gene occurs in the gene pool of a population
Macro evolution v Micro evolution
Macro-> describes the evolutionary proccesses that result in large-scale changes
Micro evolution-> the relatively small-scale evolutionary changes that take place withing a species
