3.7 Genetics, populations, evolution and ecosystems Flashcards
What does autosomal linkage mean?
- Two alleles found on the same autosome
- They do not assort independently and are linked
What does codominance mean?
- When both alleles are expressed in the phenotype at the same time
What are the Hardy-Weinburg equations?
What does each stand for?
(alleles) p + q = 1
(phenotypes) p^2 + 2pq + q^2 = 1
What are the causes of genetic variation?
- Mutations
- Meiosis (crossing-over, independent assortment)
- Random fertilisation of gametes
What else can cause phenotypic variation, aside from genetics?
The environment
Explain how natural selection occurs.
- Random mutations produce new alleles and variation within a population
- Allele could be beneficial under specific selection pressures, differential reproductive success
- Beneficial allele passed down to offspring over many generations, frequency of allele increases until the species evolves
What can impact allele frequency in a population aside from natural selection?
- Genetic drift = random chance impacts which alleles get passed on, some alleles lost and some favoured (larger impact in smaller populations)
- Founder effect, genetic bottleneck
What may disruptive selection cause?
Polymorphism (distinct phenotypes in a population) and then sympatric speciation
What is the main difference between allopatric and sympatric speciation?
- Allopatric is caused by geographical isolation
- Sympatric caused by reproductive isolation
Explain how sympatric specciation may occur.
- Random mutations occur, new alleles arise
- These new alleles cause reproductive isolation and no gene flow between the populations
- Alleles passed on to offspring
- Over many generations, allele frequency increases
- Two populations become different species, can no longer reproduce and produce fertile offspring
Explain how allopatric speciation may occur.
- Two populations geographically isolated, no gene flow
- Random mutations in each population, new alleles produced that may be beneficial
- Populations experience different selection pressures in their different environments
- Differntial reproductive success for individuals in the two populations due to different beneficial allele
- Different alleles passed down to offspring over many generations, allele frequency increases in each population
- Until the two populations can no longer breed to produce fertile offspring, become seperate species
Explain 4 different causes of sympatric speciation.
- Mechanical variation = anatomical differences causing variation
- Temeperal variation = different breeding seasons
- Behavioural variation = mutations affecting courtship behaviours
- Hybrid sterility = can’t produce viable gametes
What is an ecosystem?
Interactions between all the living organisms within a community and the non-living components
What is a community?
Interactions between populations of different species
Give examples of abiotic and biotic factors.
Abiotic = temperature, light, pH, water
Biotic = predator-prey relationships, mating
What is a population?
- Group of organisms of the same species occupying the same space at the same time
- Can possibly interbreed to produce fertile offspring
How can you estimate the size of a population using the mark-release-recapture method?
- Capture sample of species
- Mark in a way which will not impact survival (for example make them more obious to predators)
- Release, allow them time to distribute evenly in population
- Recapture and count marked individuals
- Estimate population size:
N = (n1 x n2)/ m2
What assumptions are made when using the mark-release-recapture method to estimate popualtion size?
- No death between 1st and 2nd capture
- No migration in or out of population between 1st and 2nd capture
- Marked individuals are given enough time to evenly distribure throughout population before 2nd capture
- Marking has no impact on chances of survival
How can you estimate population size using a quadrat?
- Use a map of the area and randomly select coordinates using a random number generator
- Place a quadrat at each coordinate, count the number of individuals
- Calculate the mean number of individuals from a large number of samples taken using the quadrat
- Multiply this number up to the size of the area
What does a niche refer to?
The role of the individual in the habitat it lives in
Why do species not occupy the same niche?
Competitive exclusion principle:
- Two species can’t survive if they occupy the same niche, one of them will outcompete the other
- There will always be slight differences that allow the other species to survive more (diet, mates etc)
What is a habitat and microhabitat?
Habitat = where an organism lives, characterized by the abiotic/biotic conditions
Microhabitat = smaller unit of a habitat
What is carrying capacity?
The maximum stable population size that an ecosystem can support.
When does primary succession occur?
Newly formed hostile, arid land with no plants or organic material (soil)
(volcanic eruption, shifting sand dunes)
