selection Flashcards
what determines an organisms characteristics (phenotype)
the organisms genotype (all the alleles it has) and its interaction with the environment
what is an allele
its a different version of the same gene
what is genetic diversity (gene pool)
the number of different alleles of genes in a population
what affect do mutations have in a population
they introduce new alleles which could provide selective advantage/disadvantage or neutral (does nothing)
give the definition for natural selection
process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population
give 3 factors that affect reproductive success and differential survival
predation disease and competition
what does selection pressure determine
it determines the spread of an allele within the gene pool, and can be both abiotic or biotic
give some abiotic selection pressures and their impact on populations
pH of soil
humidity
light intensity
temperature
salinity
usually has same impact or small or large population
give some biotic selection pressures and their impact on populations
number of predators
pathogens
presence of mate
food availability
number of prey available
usually has a bigger impact on bigger population
what are 3 the adaptations of an organism called
anatomical
physiological
behavioural
what are anatomical adaptations
body shape, colour, fur texture, structural features
what are physiological adaptations
internal functions of an organism that help them thrive in a specific environment
what are behavioural adaptations
something an animal does usually in response to some type of external stimulus in order to survive actions to aid survival
what are the steps for stabilising selection
- there’s selection AGAINST both extremes
- only mean phenotype will have reproductive success
- alleles for mean phenotype are passed on to future generations in greater numbers
- overtime, frequency of mean alleles, coding for mean phenotype, INCREASES
- alleles coding for both extreme phenotypes decrease
what are the steps for directional selection
- selection for only one extreme
- individuals with advantageous allele have increased reproductive success
- alleles for one extreme are passed on to future generations in greater numbers
- overtime, frequency of this extreme allele, coding for extreme phenotype INCREASES
- alleles coding for the other extreme phenotype decreases within population
what is evolution by natural selection a change in
it is a change in the allelic frequencies within a population
explain how selection occurs in living organisms
- there’s variation due to formation of new alleles by mutation
- selection pressure in habitat (abiotic/biotic)
- selection advantageous phenotype coded for by advantageous allele
- organisms better adapted for survival will reproduce so there’s differential reproductive success
- advantageous phenotype selected for organism survive and reproduce
- this occurs over many generation
- leading to an increase in advantage allele frequency
what is differential reproductive success
when some individuals leave more offspring in the next generation than do others, due to their advantageous alleles.
define gene mutation and explain how a mutation
-can have no effect on individual
- a positive effect on individual
(4)
- gene mutation is a change in base sequence of DNA forming a new allele
- there will be no affect on an individual because DNA sequence is degenerate so more than one codon codes for one amino acid
- however mutation can result in advantageous allele coding for a gene
-that will give increased reproductive success
when do you use logarithms
when you have a large range of values
what is a colony (of bacteria)
a cluster of cells or colonies which arise from a single bacterium by asexual reproduction
why do you perform a serial dilution
to count the bacteria colonies when its too concentrated
how do you do a serial dilution
- take a sample of 1 part of bacteria from medium and mixing it with 9 parts water. this is a 1/10 dilution
take 1 ml of previous dilution and add 9ml of sterile water and mix well to create a 1/100 dilution
why is it not good to use a low dilution
the count is unlikely to be accurate because there are too many cells so they will be overlapping
