3 Flashcards
Suggest how a small organism, which can lay up to 400 eggs that develop into adults within 1-2 weeks and has distinct characteristics between males and females, is useful for studying genetic crosses
> Large number of eggs = improves reliability / use statistical tests / representative / large sample size / reduces sampling error
Small size = easily kept / stored
Easy to identify females from males
Short generation time = results obtained quickly
Suggest reasons for conserving woodlands
>Protecting habitats / niches >Protecting endangered species maintains biodiversitt >Reduces greenhouse effect >Source of medicnes / chemicals / wood >Reduces erosion / eutrophication
Summarise the ways in which new species may arise
> Isolation - geographically or reproductively
Genetic variation
Natural selection
Time
What are ecosystems described as?
Dynamic - constantly changing
What are the conditions for the Hardy-Weinberg principle?
> Organisms = diploid + reproduce sexually
Alleles not sex-linked - distributed equally between both sexes
No emigration or immigration
No mutations
No natural selection
Large population
Random mating (all genotypes equally likely to mate) + no mating between individuals of different generations
What are the other sources of genetic variation?
> Random fertilisation of gametes
>Fusion of gametes is a matter of chance, and independent of each other
What are the two types of succession?
Primary succession and secondary succession
What are the types of variation?
> Discontinuous - discrete groups, result due to genetic factors, represented by bar graphs
Continuous - polygenic with characteristics showing a range, result due to environmental factors, represented by normal distribution curves
What assumptions are made when using the mark-release-recapture method?
> No significant population changes due to immigration / emigration
Marking hasn’t affected the individuals’ chances of survival
Marked animals have been given sufficient time to thoroughly mix with population
No significant population changes due to deaths / births
What does the Hardy-Weinberg principle calculate?
> Allele frequency, using a mathematical model
p + q = 1.0
p2 + 2pq + q2 = 1.0
Where p = dominant, q = recessive, and pq = heterozygous
What does the Hardy-Weinberg principle predict?
> Frequencies of alleles in a population don’t change from one generation to the next
Only reliable/true if certain conditions are met
What is a genetic bottleneck?
> Large reduction in size of population due to environmental events (i.e. natural disasters)/human activities
Produces a smaller population with reduced genetic diversity
Can lead to speciation
What is allopatric speciation?
> Geographical isolation due to physical barriers e.g. oceans, rivers
Separated populations experience different selection pressures due to different environmental conditions
Selection in favour of individuals with advantageous alleles
Leads to change in allele frequency over time
What is genetic drift?
When chance, rather than environmental factors, results in a change in allele frequency
What is meant by uniformly distributed?
Organisms are equally spread
What is sympatric speciation?
> Population become reproductively islated without becoming geographically isolated
Variation may occur due to mutations within population
Allele frequency changes over time
Individuals unable to interbreed successfully + produce fertile offspring
What is the ‘competitive exclusion principle’
> If two species were to occupy the same niche
One would outcompete the other
Impossible to coexist
What is the difference between dihybrid and monohybrid?
> Mono -> inheritance of a single characteristic
>Di -> inheritance of two characteristics at the same time
What is the difference between dominant and recessive?
> Dominant => allele is always expressed when at least one copy present
Recessive => allele is only expressed when two copies present
What is the difference between heterozygous and homozoygous?
> Hetero => only one type of allele is carried
>Homo => two different alleles carried
What is the expected phenotypic ratio of the offspring of homozygous recessive and homozygous dominant parents in a codominant cross?
>F1 = 100% heterozygous >F2 = 1:2:1 (25% homozygous for each allele, 50% heterozygous for both alleles)
What is the expected phenotypic ratio of the offspring of homozygous recessive and homozygous dominant parents in a dihybrid cross?
>F1 = 100% heterozygous >F2 = 9:3:3:1 (DR:Dr:dR:dr)
What is the expected phenotypic ratio of the offspring of homozygous recessive and homozygous dominant parents in a monohybrid cross?
>F1 = 100% heterozygous >F2 = 3:1 (dominant:recessive)
What is the primary source of genetic variation?
Gene mutation, i.e. a change to the sequence of DNA nucleotide bases, leading to production of new alleles
What may be the result of reproductive separation?
> New species arise from existing species (speciation)
>When genetic differences => inability of members of the populations to interbreed + produce fertile offspring
What may cause a change in allele frequency?
>Mate-selection >Migration >Natural selection >Genetic drift - random change in allele frequency due to chance >Mutation
What may individuals within a population of a species show?
> A wide range of variation in phenotype
>Due to genetic and environmental factors
What would be the expected phenotypic ratio of a dihybrid cross involving a dominant epistatic allele?
> At least one copy of dominant epistatic allele masks expression of other gene
Heterozygous x heterozygous = 12:3:1 (dd:dr:rr)
What would be the expected phenotypic ratio of a dihybrid cross involving a recessive epistatic allele?
> Two copies of recessive allele masks expression of other gene
Heterozygous x heterozygous = 9:3:4 (dd:dr:rr)
Example: lack of melanin masks expression of pigment colour
When are quadrats used for estimating the size of a population?
For slow-moving or non-motile organisms
