Evolution Flashcards
What is evolution?
The change over time in the proportion of individuals in a population differing in one of more inherited traits
What is an allele?
A different forms a gene
During evolution, changes in allele frequency occur due to…
Non-random processes of natural and sexual selection and random process of genetic drift
Selection results in the non-random…
Increase in frequency of advantageous alleles
Decrease in frequency of deleterious alleles
What does natural selection act on?
Genetic variation within a population
What does variation in traits arise as a result of?
Mutation- the original source of new DNA sequences
What are novel alleles?
New versions of genes
New DNA sequences can be…
Novel alleles
Most mutations are…
Harmful or neutral but in rare cases can be beneficial to the fitness of the individual
Stages of natural selection
- Population produces more offspring than the environment can support
- Individuals with variations that are better suited to their environment tend to survive longer and produce more offspring
- Breeding passes on those alleles that confer an advantage to the next generation
What is sexual selection?
Non-random process involving the selection of alleles that increase an individuals chances of mating and producing offspring
Sexual selection can be due to…
Male-male rivalry or female choice
What is male-male rivalry?
When size, strength or weaponry increases males’ access to females through conflict, large size and weaponry often go hand in hand
e.g. elephant seal (large size) and stag (weaponry)
Alleles that increase an individual’s chances of mating and producing offspring are…
Species specific
Larger, stronger and greater weaponry leads to a…
Successful male as these are fitness characteristics that will be advantageous to offspring
Female choice involves…
Females assessing the fitness of males during rutting season and lekking
What is rutting season?
A recurrent period of sexual excitement and reproductive activity in certain male ruminants
What is lek-mating?
A lek is an aggression of male animals gathered to engage in competitive displays to entice visiting females surveying prospective partners for fitness
Females assess… of the fitness of males
Honest signals
What do honest signals indicate?
Favourable alleles that increase the chances of offspring survival
Low parasite burden suggesting a healthy individual
What do many species exhibit as a product of sexual selection?
Sexual dimorphism (distinct differences between sexes, typically size and colouration)
Females are generally…
Males are usually more…
Inconspicuous
Conspicuous
Reversed sexual dimorphism occurs in certain species such as…
Birds of prey e.g. peregrine falcon, males are smaller in size than females to be better adapted for hunting small prey for young during breeding season
Genetic drift occurs when…
Chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
What is a population bottleneck?
Event that drastically reduces population size
Bottleneck effect may be caused by…
Environmental disaster
Overhunting (hunting species to the point of extinction)
Habitat destruction that results in the death of organisms e.g. deforestation, coral bleaching
Disease e.g. devil facial tumour disease, an aggression cancer
What is the founder effect?
Occurs when a few members of the population are isolated from the larger population so the gene pool of the new population is not representative of the original one
Genetic drift has a greater effect in… as…
Small populations, alleles are more likely to lost from the gene pool
How is a gene pool altered by genetic drift?
Under or over-representation of certain alleles and allele frequencies change
What are selection pressures?
Environmental factors that influence which individuals in a population can pass on their alleles
Selection pressures are either…
Biotic- competition, predation, disease, parasitism
Abiotic- changes in temperature, light intensity, pH or salinity
What increases the rate of evolution?
Strong selection pressures
The Hardy-Weinberg principle states that…
in the absence of evolutionary influences allele and genotype frequencies in a population will remain constant over the generations, this stability is known as the Hardy-Weinberg equilibrium
Name evolutionary influences
Natural selection
Sexual selection
Genetic drift
Mutation
What are the conditions for maintaining the Hardy-Weinberg equilibrium?
No natural selection
No mutation
No gene flow (through migration in or out of population)
Random mating
Large population size
The HW equilibrium can be used to…
Determine whether a change in allele frequency is occurring in a population over time, changes suggest evolution is occurring
Equation to calculate allele genotype ad phenotype frequencies in populations
p2 + 2pq + q2 =1
p2= frequency of homozygous dominant genotype
2pq= frequency of heterozygous genotype
q2= frequency of homozygous recessive genotype
What is fitness?
An indication of a individual’s ability to be successful at surviving and reproducing, refers to the contribution made to the gene pool of the next generation by individual genotypes
What is absolute fitness?
Ratio between frequency of individuals of a particular genotype after selection to those before
What is relative fitness?
Ratio of number of surviving offspring of a particular genotype to the number of surviving offspring per individual of the most successful genotype
Equation for absolute fitness
frequency of particular genotype after selection
frequency of particular genotype before selection
Equation for relative fitness
no. of surviving offspring of particular genotype
no. of offspring surviving per individual of most successful genotype
What is co-evolution?
The process by which two or more species evolve in response to selection pressures imposed by each other
What is the Red Queen hypothesis?
When a change in traits of one species acts as a selection pressure on the other species, species in these relationships must adapt to avoid extinction
What is symbiosis?
Co-evolved intimate relationship between members of two different species, impact for individuals can be positive, negative or neutral
3 types of symbiotic interactions
Mutualism
Commensalism
Parasitism
Co-evolution is often seen in pairs of species that have…
Symbiotic interactions
What is mutualism?
Both species involved in interaction are interdependent on each other for resources or other services, both species gain from relationship
Often generates a structural compatibility between mutualistic partners
+/+ interaction
What is commensalism?
Only one of the species (commensal) benefit (nutritional) and host is unaffected, usually involves commensal utilising dead parts/waste of host or taking advantage of disturbances caused by host
0/+ interaction
What is parasitism?
One species (parasite) benefits in terms of energy and nutrients while the other (host) is harmed as it loses energy and resources, incurs further costs for the host in defending it’s tissues from parasitism attack
+/- interaction
