Unit 7 Flashcards
(14 cards)
Describe allopatric speciation (5)
-Geographic isolation splits the population into two
-prevents interbreeding between the two populations so separate gene pools form
-different random mutations occur in each populations and different selection pressures act on each population
-causes allele frequency to change differently in each population, so they become genetically diverse
-over time, they become two species as they cannot produce fertile offspring.
Describe sympatric speciation (4)
-random mutation within a population causes reproductive isolation for a few individuals
-this prevents interbreeding between the populations and separate gene pools form
-the new populations will pass on their alleles to their offspring and the population will rise
-the two populations form two separate species as they no longer can have fertile offspring with each other.
Describe how to sample a non mobile organism to estimate the population in an area
-divide the area into a grid
-use a random number generator to obtain coordinates to place a quadrat
-count the number of the organisms in the quadrat
-use a large sample and calculate a mean per quadrat
-calculate total population through dividing the area of the populations by the area of the quadrat and multiple the answer by the mean number of organisms per quadrat
Describe how succession occurs
-colonisation by pioneer species
-the pioneer species changes the environment
-the environment becomes less hostile for new species and the previous species gets outcompeted
-there’s an increase in biodiversity
-leading to the climax community
Describe the effect of an increased plant/animal diversity on an ecosystem (3)
-increase in plant diversity leads to more different food types for animals
-increase in animal diversity leads to an increase in predator species
-increase in more niche/habitat
Outline the method ‘mark, release and recapture’ (4)
-capture sample, mark and release
-ensure method of marking is not harmful or does not effect survival
-allow time for sample to randomly distribute before collecting another sample
-use equation: population = number in first sample x number in second sample divided by number of recaptures in second sample
Give four causes for genetic variation in organisms (4)
-mutation
-crossing over
-independent segregation
-random fertilisation
Give the conditions under which the Harvey Weinberg principle applies (5)
-no mutations arise
-random mating
-large population
-population is isolated
-no selection pressures
Give five assumptions for the method ‘mark, release and recapture’ (5)
-no emigration/immigration
-no losses to predation
-large sample size
-death rate is equal to birth rate
-marking does not effect surival
Give two features of a climax community (2)
-same species present for a long time
-abiotic factors constant over time
Explain why speciation takes a long time (3)
-initially there are a few animals with a favourable mutation
-the individuals with the favourable mutation are more likely to survive and have offspring that they’ll pass the allele down to
-takes multiple generations for the favourable mutation to become the most common allele
In genetic crosses, the observed phenotype ratios obtained in the offspring are often not the same as the expected ratio, suggest five reasons why (5)
-small sample size
-linked genes
-epistasis
-lethal genotypes
-fusion of gametes is random
If a gene is sex linked on the X chromosome, why is the phenotype more common in XY organisms (2)
-XY organisms only need one allele
-XX organisms need two recessive alleles
Describe natural selection in resistant strains (5)
-some individuals in a population are naturally resistant to pesticide/antibiotic
-due to mutation
-these survive pesticide/antibiotic whilst non-resistant are killed
-reproduce and pass on allele for resistance
-over time the frequency of resistant allele increases
