4 Flashcards
When is the mark-release-recapture method used for estimating the size of a population?
For mobile organisms
Where does primary succession occur?
> On newly formed or exposed land
>No soil or organic material, e.g. bare rock
Where does secondary succession occur?
> On land cleared of plants
>But soil remains
Why are males more likely to show recessive phenotypes for sex-linked genes?
> Males only have one X c/s = only one allele for sex-linked genes
Y c/s has no homologous portion for many genes
Characteristic of certain one copy alleles expressed, even if recessive
Why are recessive X-linked alleles always represented in a man?
> Males have one allele / X chromosome
>Females have two X chromosomes, therefore need two recessive alleles, otherwise will be masked by a dominant allele
Why are the observed results of genetic crosses different to predicted results?
> Random fertilisation of gametes -> fusion of gametes is an independent event; equal chance of any two gametes fusing
Small sample size
Mutation
Selection -> death as a result of combination of alleles
Why does evolution by genetic drift usually have a greater effect on smaller populations?
> Chance has a greater influence on smaller populations
>Smaller variety of alleles
Why does population growth exhibit a period of slow growth, or a lag phase
> Delay before start of rapid growth
>Due to, for example, synthesis of enzymes able to digest food source; time to reach sexual maturity
Why does succession occur?
> Species present at any one time causes habitat change
Abiotic and biotic factors altered
New, better-adapted species out-compete old species + establish themselves
Why don’t mutations in one species ‘spread’ to other species?
> Mutations are random/spontaneous, rate of which affected by environment
Different species do not interbreed
Alleles not passed on
Why is there a time lag between a change in environmental conditions and resistance to the change within species?
> Initially, one/few individuals with favourable allele (due to pre-existing variation)
Those individuals have more offspring
Over many generations, favourable allele becomes most common allele
Why may population growth slow down?
> Environmental resistance
>Limiting factors arise, example: shortage of food, increased predation or accumulation of waste
Why may the results of a dihybrid cross involving linked genes differ from the expected ratio?
> Random exchanging of genetic material between non-sister chromatids during first meiotic division
Results in recombinant chromosomes
Linked genes may be separated, so not inherited together
What is allopatric speciation?
> a mode of speciation that occurs when biological populations of the same species become isolated from each other to an extent that prevents or interferes with gene flow
