populations and evolution Flashcards
define gene pool
all the alleles of all the genes of all the individuals in a population at a given time.
define allele frequency
the number of times an allele occurs within the gene pool
Define the Hardy-Weinberg principle
-Mathematical equation used to calculate frequencies of alleles of a particular gene in a population.Based on the following assumptions:
- No mutations
- Isolated population - no flow of
- alleles in or out
- No selection - alleles equally
likely to be passed on
- Large population
- Random mating”
State the 5 conditions that must be met in order to apply Hardy-Weinberg principle
“o mutations
Large population
No flow of alleles in or out of population
No selection
Mating is random
What is the equation to determine allele frequency?
p+q=1
What is the equation to determine genotype frequency?
P2 + 2pq + q2 = 1
Describe variation due to genetic factors.
-Variation due to the different alleles in a population.
-Usually controlled by a single gene, distinct categories with no intermediates (eg A,B,AB,O blood types),
-not influenced by environmental factors.
-Genetic variation arises from mutations, meiosis, random fertilisation of games.
mutations
sudden changes to gene and chromosomes which may or may not be passed on
meiosis
nuclear division that produces new combinations of alleles before they are passed into the gametes all which are therefore different
random fertilisation of gametes
in sexual reproduction this produces new combos of alleles and the offspring are therefore different from parents
-which gamete fuses with which at fertilisation is a random process further adding to variety of offspring two parents can produce
Describe variation due to environmental influences.
-Environmental factors affect the way in which an organisms genes are expressed, the gene sets the limits but the environment determines where within this the organism lies. -Examples of environmental conditions: pH, climatic conditions, availability of food. Environmental variation affects characteristics controlled by polygenes (more than one gene)
What are the features of largely genetic variation?
-caused by a single gene
-few distinct forms - no intermediates
-represented by bar or pie chart
Describe the interaction between genes and the environment
genes set the limits of characteristics
the environment determines where an organism lies within these limits
Explain the role of overproduction of offspring in natural selection.
-The death rate for organisms is high. -Organisms compensate for this by overproducing.
-The vast numbers of offspring allow enough organisms to survive despite the high death rate due to predation, competition for food etc.
Explain the role of variation in natural selection.
-Variation is important in natural selection as environmental conditions change over time.
-A wide range of genotypes and therefore phenotypes in a population will mean some have the characteristics to survive in most new sets of circumstances.
Describe stabilising selection.
Stabilising selection eliminates extremes of the phenotype range. Occurs where environmental conditions are constant and limits opportunity for evolution by natural selection.
Describe directional selection.
-For many phenotypes there will be a range of genetically different individuals.
-If this continuous data is plotted on a graph it forms a normal distribution curve.
-The mean represents the optimum value under existing conditions.
-If environmental change occurs the optimum value also changes.
Describe disruptive selection.
-Disruptive selection is opposite to stabilising selection and favours extremes in phenotype at the expense of the mean.
-Not common but he most significant in producing evolutionary change
Explain the effects of each form of selection on evolution.
-Stabilising selection: limits capacity for evolutionary change
-Directional selection: causes evolution favouring one extreme
-Disruptive selection: causes the most evolutionary change”
Explain how selection affects allelic frequencies.
-Allelic frequency is the number of times an allele occurs within the gene pool.
-This is affected by selection which in turn is affected by environmental conditions.
Explain how new species are formed.
-New species are formed by speciation - the evolution of new species from existing ones.
-New species form when there is reproductive separation and then genetic change due to natural selection.
Explain how populations can become geographically isolated.
-Geographic isolation is any physical barrier between two populations that prevents them interbreeding.
-This may include; oceans, rivers, mountain ranges, deserts.
-What constitutes a geographical barrier is determined by the nature of the organisms being separated
Describe allopatric speciation
-Populations separated by geographical barrier,
-conditions on either side of the barrier vary,
- natural selection influences the two populations differently,
-two populations evolve leading to adaptations to their local conditions,
-reproductive separation occurs (populations can no longer interbreed)
