D4.1 Flashcards
what is natural selection
1) Organism are __over reproduced___ leading to an increase in __competition___
2) __Mutaton_ creates gene&c varia&on
3) Organisms with the ___advantageous alleles___ will be able to adapt the __selection
pressure__
4) *Organisms with the advantageous alleles will ___survive and reproduce___
5) __Passing on__ the advantageous alleles to the offspring
6) Increasing the advantageous __allele frequency___ in the gene pool over
genera&ons
what does mutation do
Mutation generates new alleles and sexual reproduction generates new combinations
Sources of variation
Mutations in DNA
Meiosis
Sexual reproduction
Variation: Mutations in DNA
Some mutations can lead to genetic diseases which could kill an individual
Other mutations can be beneficial (e.g. enhanced ability or some features which allows the individual to survive better)
However, most of the time, mutations produce effects that are neither useful nor harmful (cannot rely on mutation alone to improve the chance of survival)
Variation: Meiosis
Meiosis is a kind of cell division in which (reproductive cells) male and female gametes are made
- sperms and ova (singular: ovum) in animals
- male gametes in pollen grains and female gametes in ovules in flowering plants
THey only have half the amount of chromosomes (DNA) comparing to the somatic cells (any cell of a living organism other than gamete)
Variation of gametes arise mainly from the process of random orientation during metaphase 1. The lining up of chromosomes is random. crossing over helps shuffle genetic material and increases genetic variety further
Variation: Sexual reproduction
Possessing some characteristics may favour an individual which may affect survival and opportunities to reproduce
Examples of variation of sexual reproduction
Birds with more colourful feathers to attract mates
Animals with stronger leg muscles to run away from predators
Organisms with enzymes that can stay active for a larger range of temperature/pH
what is asexual reproduction
Asexual reproduction produces genetically identical offspring/second generation
what is overproduction
Many of the living organisms produce a lot of offspring (but the number of individuals in species remains more or less constant, so there must be a high mortality rate
It requires a large amount of energy and nutrients to produce a large amount of seeds, spores or eggs (this can affect the survival rate of the parents especially when the resources are limited)
This is to maximise the chances of some offspring surviving
carrying capacity
Carrying capacity refers to the maximum number of organisms that an environment can provide for, resources like food, water, space, sunlight will determine the carrying capacity of an environment
what is selection pressure
Selection pressures are external agents which affect an organism’s ability to survive in a given environment
density dependent factors
PANDA
Predators
Availability of resources (shelter, water)
Nutrient supply (i.e. food source)
Disease / pathogenic spread
Accumulation of wastes
density independent factors
PAW
Phenomena (e.g. natural disasters)
Abiotic factors (e.g. temperature, CO2 levels)
Weather conditions (e.g. floods, storms, etc.)
what is intraspecific competition
Competition between individuals from the same species
Compete for the same type of resource
Example of adaptations for intraspecific competition
plover egg and chicks
effective camouflage protect them from eaten by predator (if some mutations cause the shell or the chicks to become attractive to predators, then those mutated genes would not be able to pass to the next generation)
Heritable traits
Heritable traits refers to features or characteristics that are driven by the organism’s DNA (not due to acquired skills or ability), these traits can be passed down to the next generation
acquired traits
Acquired characteristics refers to some features that the organisms acquired through its lifetime, these characteristics cannot be passed down to the offspring
Sexual selection
Male compete for access to females, who being present to mate with females, and even whose sperm gets to fertilise her eggs. For example, male damselflies scrub sperm out of the female reproductive tract when mating
sexual dimorphism
Sexes of the same species display different morphological characteristics
Male birds with colourful and shiny features as an indication of the health of the male
Female birds with cryptic coloration for camouflage and able to hide from predators
Female choice
Females choose which males to mate with, how long to mate, and even whose sperm will fertilise her eggs. Some females can eject sperm from an undesirable mate.
what is gene pool
A gene pool consists of all the genes and their different alleles, present in a population
inbreeding
Refers to the mating of close relatives in species
Reduces the genetic diversity
Allele frequency
it is the measure of the proportion of a specific version of a gene in a population
Alleles and evolution
Immigration and emigration may change the allele frequency of a population
Mutations may introduce new alleles to a population
Some alleles may disappear in a population if the individuals carrying those alleles die
Some alleles that are not advantageous to the survival of organisms in a population (e.g. disease causing) may have different effects on the population depending on the nature of the alleles (dominant vs recessive traits)
stabilising selection
Where an intermediate phenotype is favoured at the expense of both phenotypic extremes
This results in the removal of extreme phenotypes (phenotypic distribution becomes centrally clustered to reflect homogeneity)
stabilising selection example
Human birth weight
Babies of low weight lose heat more quickly and get ill from infectious diseases more easily. Babies of large body weight are more difficult to deliver through the pelvis. Medium weight babies have a much lower mortality and hence the frequency of medium weight babies increases
directional selection
Where one phenotypic extreme is selected at the cost of the other phenotypic extreme
This causes the phenotypic distribution to clearly shift in one direction (towards the beneficial extreme)
directional selection example
Darwin finches
Years of drought caused the medium ground finches living on Daphne Major to shift the beak size from a normal distribution to mostly having larger beaks to help the finches to crush larger and drier seeds produced by drought tolerant plants.
disruptive selection
Where both phenotypic extremes are favoured at the expense of the intermediate phenotypic ranges
This causes the phenotypic distribution to deviate from the centre and results in a bimodal spread
disruptive selection examples
Different morphologies of the tadpoles of spadefoot toads
One is an omnivorous diet and one is strictly carnivorous diet. Less overlapping of diet choices within the same population and reduce intraspecific competition
Natural selection case studies
Antibiotic-resistant bacteria
Peppered wing moth
Galapagos finches aka Darwin’s Finches
antibiotic-resistant bacteria
Through sexual reproduction and mutation, cause genetic variation
Some genetic variation makes some bacterium slightly more resistance to
antibiotics.
Antibiotic resistance bacteria will be __more likely to occur in a hospital__, because of the __heavy use of antibiotics__.
As those bacteria without antibiotics resistance died, there is ___less competiton___ for resources between bacterium
Bacteria with the resistant allele will survive and reproduce
Increasing the number of bacteria with antibiotic resistance allele in the gene pool.
Peppered wing moth
- Industrial revolution cause tree bark to be __darken with carbon soot__
- Moths with pale wings are less well camouflaged thus more likely to be spoged by
predator - Random mutation occurred and some moths contain _peppered-wings__.
- They are better camouflaged and more likely to survive and reproduced
- Thus the number of peppered-wing alleles will increase in the gene pool.
- Overtime the peppered-wing moth dominate the population
Galapagos finches aka Darwin’s Finches
Darwin noticed that on different islands in Galapagos Island, finches have __different beak size and shape__
This is because on different islands has ___different selection pressure_. (eg food source)
Those birds with the beak size and shape that makes them __better adapted to the environment_are more likely to survive and reproduce.
Making that allele frequency to increase in gene pool and over &me this results speciation and evolution
As the speciation is triggered by __geographical isolation__, this is known as __allopatric speciation__.
