Evolution Flashcards
Define gene mutation
- Random change in the base sequence of DNA.
- Results in the formation of a new allele.
TRUE or FALSE:
Mutations arise spontaneously during DNA replication
TRUE
Types of mutation
Substitution
Addition
Deletion
Inversion
Duplication
Translocation
Non-disjunction
Primary souce of genetic variation
random mutations
TRUE or FALSE:
Creating new combinations of alleles does not contribute to genetic variation
FALSE
Processes that create new combinations of alleles (and therefore genetic variation)
- Independent segregation of homologous
chromosomes/pairs; - Crossing over between homologous
chromosomes/pairs (non-sister chromatids); - Random fertilisation of gametes;
- (Produces) new combinations of alleles;
Sources of phenotypic diversity
Mutations that create new alleles
Crossing over
Independent segregation
Random fusion of gametes
Epigenetics
Biotic factors that act as
selective pressures
Predation
Disease
Interspecific competition
Abiotic factors that act as selection pressures
Temperature
Light intensity
Carbon dioxide concentration
Soil pH
Salinity
Humidity
Windspeed
TRUE or FALSE:
Organisms develop advantageous phenotypes because of a change in the environment.
FALSE
Random mutations produce phenotypic variation, then SELECTED FOR/AGAINST
Bullet point the key mark points for natural selection (5 marks).
- Random mutations produce phenotypic variation (within a population)
- (Named) selection pressure in the environment (biotic or abiotic)
- Organisms with (named) advantegous phenotypes are more likely to survive AND reproduce
- Pass on advantageous alleles to the next generation
- Frequency of advantageous allele increases over many generations in the gene pool
Selection that favours one
extreme phenotype
Directional
Directional selection examples
Antibiotic resistance
Giraffe neck length
Peppered moth
Type of selection that favours the mean / most common phenotype
a
Stabilising
Stabilising selection examples
Newborn / baby birthweight
Number of eggs in a birds nest
Type of selection that favours both extreme phenotypes
Disruptive
Type of selection that reduces variation and therefore the opportunity for evolutionary change
Stabilising
Types of selection that brings about evolutionary change
Directional
Disruptive
Clostridium difficile is a bacterial species that causes disease in humans.
Antibiotic-resistant strains of C. difficile have become a common cause of infection acquired when in hospital.
Explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria becoming a common cause of infection acquired when in hospital (3 marks).
- (Some bacteria have) random mutations produce alleles for resistance;
- More antibiotics used in hospital (compared with elsewhere) and exposure to antibiotics is the selection pressure
- Resistant bacteria survive & reproduce;
- Pass on resistance allele to next generation
- high frequency of resistance allele over many generations (in bacterial population);
Lactose is the main sugar in milk and is hydrolysed by the enzyme lactase. Lactase is essential to newborn mammals as milk is their only source of food. Most mammals stop producing lactase when they start feeding on other food sources. Humans are an exception to this because some continue to produce lactase as adults. The ability to continue producing lactase is known as lactase persistence (LP) and is controlled by a dominant allele.
One hypothesis for LP in humans suggests that the selective pressure was related to some human populations farming cattle as a source of milk.
Describe how farming cattle as a source of milk could have led to an increase in LP (4 marks).
- LP allele due to random mutation;
- Milk provides named nutrient /
e.g. glucose, galactose, protein and its presence act as selection pressure - Individuals with LP more likely to survive and reproduce
- Pass on LP allele to next generation
- Frequency of LP allele increases
(in the offspring/next generation); - This is an example of directional selection;
Type of selection that can lead to speciation
Disruptive
All new species evolve from existing species via a process known as ____________.
speciation
Species key features
- Capable of interbreeding to produce fertile offspring.
- Same genes but different alleles.
- (May show a) wide range of variation in phenotype.
Types of speciation
Allopatric
Sympatric
Reproductive ____________ is required for speciation.
isolation
In allopatric speciation, what causes reproductive isolation?
A geographical barrier
(e.g. river, mountain, road)
Describe and explain how a river separating two populations of lemurs can result in new specieis (5 marks).
- Allopatric speciation;
- River leads to reproductive isolation
OR No gene flow
OR Gene pools separate; - Variation due to random mutations (in different populations);
- Different selection pressures (either side of the river);
OR Different environmental/abiotic conditions/factors; - (Different/advantageous) allele/s passed on/selected OR change in frequency of alleles;
- (Eventually different species either side of river) cannot interbreed to produce fertile offspring;
n sympatric speciation, what causes reproductive isolation?
Random mutations may cause change in behaviour e.g. feeding or mate preferences / timings
TRUE or FALSE:
In sympatric speciation, reproductive isolation still occurs despite the species occupying the same habitat / area.
TRUE
Lord Howe Island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The two species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the two species are different.
Using this information, suggest how these two species of palm tree arose by sympatric speciation (5 marks).
- Occurs in the same habitat / environment / population / place;
- Random mutation/s cause different flowering times;
- Reproductive isolation
OR No gene flow
OR Gene pools remain separate; - Different allele/s passed on / selected
OR Change in frequency of allele/s - Eventually different species cannot interbreed to produce fertile offspring;
- Example of disruptive selection;
Genetic drift
Random increase OR decrease in allele frequency due to chance events
Explain why small populations are vulnerable to genetic drift.
Random loss of individuals with certain alleles;
Individuals that survive will then reproduce;
Pass on alleles to next generation;
Results in a large change in the frequency of alleles (in a shorter period of time);
Contrast genetic drift vs.
natural selection
atural selection involves differential survival and reproduction of organisms in response to selection pressures whereas genetic drift is not influenced by environmental pressures or the relative advantage of alleles.
Genetic drift is a random change in allele frequency whereas natural selection isn’t
