Inheritance and Evolution Flashcards
Define Genotype
the genetic constitution of an organism
Define Phenotype
the appearance of a characteristic due to expression of the genotype and its interaction with the environment
What are Alleles
different forms of the same gene
what is a dominant allele
an allele that is always expressed in the phenotype
what is a recessive allele
an allele that is only expressed when the genotype is homozygous recessive (two of them are present)
what are Co-Dominant alleles
where both alleles are expressed in the phenotype
what does sex linkage mean
where the gene is carried on only one type of sex chromosome (usually the X chromosome)
how would you prove an allele is recessive from a pedigree chart
- 2 unaffected parents who have an affected child
- this means that the parents must be heterozygous and carriers
how would you prove a recessive allele is not sex linked from a pedigree chart
- 2 unaffected parents produce an affected daughter
- the father wouldn’t be able to pass on a recessive allele if he was unaffected
how would you prove an allele is dominant from a pedigree chart
- 2 affected parents produce unaffected children
- both parents must be heterozygous and pass on their recessive alleles
how would you prove a dominant allele is not sex linked from a pedigree chart
- 2 affected parents produce an unaffected daughter
- the father wouldn’t be able to pass on a recessive allele so all the daughters would be affected
how would you prove a recessive allele is sex linked from a pedigree chart
- the phenotype is more commonly/only seen in males
- the males are more likely to inherit the trait as they only need to inherit one allele (females would have to inherit two)
why might the observed and expected ratios of the phenotypes of offsprings be different?
- the sample size is small therefore there is a greater sampling error
- random fusion of gametes during fertilisation
- epistasis
- linked genes (sex or autosomal)
when is a chi squared test used?
- used when we have categoric data and to compare the observed and expected ratios of the phenotypes of offspring
what are autosomal chromosomes
the non-sex chromosomes
what are autosomal linked genes
- genes that are present in the same chromosome at different loci
describe why autosomal linked genes leads to a much higher proportion of certain phenotypes than others?
- autosomal linked genes are more likely to be inherited together as there is no independent assortment and therefore fewer genetic combinations of alleles
- there will be a lower proportion of other phenotypes due to the rare occurrence of crossing over producing recombinant alleles
what is Epistasis?
- when the allele of one gene affects or masks the expression of another gene at another locus
Describe Allopatric Speciation
- Variation due to mutation gives rise to different alleles within a species
- species split into different groups due to geographical isolation
- no gene flow between different groups
- different selection pressures select different advantageous alleles
- organisms with advantageous alleles more likely to survive, reproduce and pass on the alleles increasing frequency of allele in population
- over period of time gene pools become so different that the different populations cannot interbreed to produce fertile offspring
Define Sympatric Speciation
- Variation due mutation gives rise to different alleles within a species
- these species are not geographically isolated but instead reproductively isolated due to different mating seasons or different courtship behaviour
- no gene flow between different groups and therefore different allelic frequencies
- over period of time gene pools become so different that the different populations cannot interbreed to produce fertile offspring
Describe Genetic Drift
- by chance, the allele of a particular gene is passed on to the offspring more often than other alleles of the same gene
- frequency of this allele increases over time
What type of population does Genetic Drift have the most impact on and why?
- a small population
- less genetic variation and therefore, a lower ability to adapt to changing conditions.
what conditions need to be upheld for the Hardy-Weinberg principle to be reliable?
- the population is large and isolated
- mating within the population is random
- no mutations of the gene occur
- there is no selection (all alleles are likely to be passed on to the next generation)
what is the HW equation for frequency of alleles
p + q = 1.0
- p = frequency of dominant allele
- q = frequency of recessive allele
what is the HW equation for frequency of genotypes
p² + 2pq + q² = 1.0
- p = homozygous dominant
- 2pq = heterozygous
- q = homozygous recessive
what is stabilising selection?
- natural selection favouring those with characteristics and phenotypes towards the middle of the range
what is disruptive selection?
- natural selection favouring those with characteristics and phenotypes towards the either side of the range
- most likely to cause speciation as two separate population are likely to be formed
what is directional selection?
- natural selection favouring those with characteristics and phenotypes towards one side of the range
describe when and how to use a belt transect?
- used when there is a transition in habitats and communities through an area
method:
- a tape is run along the ground in a straight line
- at regular intervals a frame quadrat is laid down along the tape and the species within it are recorded
- the percentage cover or the frequency of the species can be recorded
why is it important to use a larger number of quadrats when sampling?
to make sure the results are representative
what is the equation for estimated mean density?
total number of individuals counted ⁄ (n of quadrats x area of each quadrat)
describe the mark-release-recapture method?
- capture a representative sample of organisms from the population, record the number and mark them
- release them back into the habitat and leave them for a suitable amount of time to mix randomly into the population
- capture a second sample of organisms and count the number of marked individuals
- use equation to estimate population size
what is the equation for estimated total population
= (n marked in first sample x n captured in second sample)/n marked in the second sample
what assumptions does the ‘mark release recapture’ method rely on?
- organisms must mix randomly with the population
- organisms disperse evenly within the geographical area of the population
- changes of population size due to death birth immigration and emigration are negligible
- the marking doesn’t hinder the survival of the organisms
what are some abiotic factors that affect population size
- light availability
- pH (of soil)
- Temperature
what is interspecific competition?
- competition between different species
what is intraspecific competition?
- competition between the same species
what is a climax community?
- the end point of primary and secondary succession
- a very diverse and stable community
describe the process of succession
- pioneer species are the first to colonise an area
- the pioneer species may change the abiotic environment making the environment less hostile and making it more suitable for new species with different adaptations to colonise the habitat
- the new species may outcompete the previous reducing their abundance
- succession usually proceeds to form a climax community which is stable due to the complexity and variety of the food webs.
how is succession managed/prevented?
grazing - seedlings of herbaceous plants and shrubs are continually eaten preventing any succession beyond grassland
ploughing - the seedlings are broken up and buried preventing germination and the use of herbicides maintains an established community
