2 Flashcards
Describe how the mark-release-recapture method can be used for estimating the size of population
> Capture a large sample of organisms being studied + count
Mark each organism without causing harm
Release marked organisms back into habitat
Capture a second large sample from the same population after a certain time
Count the total no. caught + total no. marked
Describe predation
> An organism (predator) feeds on another organism (prey)
>Predator and prey populations linked
Describe stabilising selection
> Selection in favour of individuals with mean phenotypes; selection against extremes
Occurs in unchanging environment
Reduces range of possible phenotypes, and SD from mean
Describe the log phase of population growth
> Period of rapid growth
Exponential increase, rather than arithmetic
Growth is rapid due to lack of limiting factors
Different species occupy different ecological niches.
Explain the advantage of species occupying different niches.
Less competition for food / resource
Explain how evolutionary change over time has resulted in a great diversity of organisms
> Diversity of life is the result of speciation + evolutionary change over millions of years
Original population of organisms divided, became separate species
Explain how microorganisms contribute to the increase in temperature during processing of organic waste
> Respiration / metabolism / ammonification
>Releases heat
Explain how natural selection is a method by which evolution occurs
> Organisms with phenotype that increases their chance of survival
More likely to survive, reproduce + pass on advantageous alleles to offspring
Leads to change in allele frequency over time/many generations
Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in just one bacterium
> Frequent use of antibiotic creates selection pressure
Bacteria with mutation / resistance have selective advantage over others
Great chance of survival -> reproduce + pass on advantageous allele in great numbers
Frequency of advantageous allele increases in subsequent generations
Frequency of resistant bacteria increases in subsequent generations
Explain why actual numbers of offspring may be different from expected
> Offspring ratios are a probability / arise by chance
Gametes not produced in equal numbers
Fertilisation / fusion of gametes is random
Small sample
Give an example of codominance
> Alleles for Hb (HN) and sickle-cell anaemia (HS)
HNHN = normal Hb, HSHS = sickle-cell anaemia
HNHS = sickle-cell trait, mixture of normal Hb and sickle Hb
Give an example of multiple alleles
> ABO blood group system - three alleles for blood type
>Codominant IA and IB, recessive IO
Give the differences between X and Y chromosomes
> Y c/s = smaller, carries few genes + shaped differently
Most genes on sex c/s only carried on X c/s (i.e. are X-linked genes)
Most of X and Y not homologous i.e. short pairing region
How do multiple alleles of a gene arise?
> Mutations
>Occuring at different positions in gene
How does interspecific competition arise?
> When two different species in the same habitat require the same resource
Resource is in short supply
If niches of two species are similar, more likely for interspecific competition to occur
How does meiosis further genetic variation?
> Chromosomal crossover - sections of chromatids exchanged between bivalents = chromosome with new allele combo
Independent assortment - maternal + paternal chromosomes randomly shuffled; results in different combo of alleles in gamete
How is the data from the mark-release-recapture method used to estimate the total population size
> Lincoln index
>Total no. of animals in population = (no. sample 1)(no. sample 2) / (no. marked sample 2)
How many alleles for each gene do gametes carry compared to diploid cells?
> Only one -> when gametes from each parent fuse, alleles form genotype of offspring
Diploid cells -> two
How many antigen-determining alleles will be present in a white blood cell? Give a reason for your answer
> Two
>White blood cells are diploid / alleles are present on each chromosome of a homologous pair
How may differences in the gene pools of two population accumulate?
Reproductive separation/isolation
How may reproductive isolation occur?
> Seasonal - individuals within the same population have different flowering/mating seasons or sexually active at different times
Mechanical - changes in reproductive organs, prevent successful mating
Behavioural - group of individuals develop courtship rules, aren’t attractive to main population
How may the results of a genetic cross show autosomal linkage?
> Expected ratio not seen
Parental phenotypes overrepresented / more offspring with same genotypes as present
Non-parental phenotypes underrepresented / fewer recombinants / offspring with new combinations of parental alleles
Evidence that genes do not assort independently i.e. not separated by independent segregation during meiosis
If two genes are closer together on an autosome, what is their relationship?
> More closely linked
>Less likely to be split during chromosomal crossover
In a diploid organism, what may the alleles at a specific locus be?
> Homozygous or heterozygous
>e.g. in sister chromatid pair (i.e. chromosome), one chromatid has H allele, other has h allele
In mammals, how is sex determined?
>Females = two X chromosomes (XX) >Males = one X, one Y (XY)
List examples of abiotic factors
> Temperature
Light intensity
Availability of water / NaCl / carbon dioxide / oxygen
Mineral content / pH / water-holding and drainage capacities of soil
On islands in the Caribbean, there are almost 150 species of lizards belonging to the genus Anolis. Scientists believe that these species evolved from two species found on mainland USA. Explain how the Caribbean species could have evolved.
>Geographical isolation >Separate gene pools / no interbreeding / gene flow (between populations) >Variation due to mutation >Different selection pressures >Differential reproductive success >Leads to change in allele frequency
Scientists may use percentage cover rather than frequency to record the abundance of a particular species present. Suggest why
> Difficult / too many to count
>Individual organisms not identifiable / too small to identify
State two factors which causes variation in population size
> Effect of abiotic factors
>Interactions between organisms
Suggest economic consequences of the spread of a major pest species
> Cost of control / removal
Cost of restoring habitat / conservation
Loss of income from tourism / recreation
