Chapter 17- Selection and Evolution Flashcards
State 4 ways genetic variation is caused
- Independent assortment
- Crossing over
- Random fusion of gametes & random mating
- mutation
The phenotype of an organism is a result of interaction between______ and _____________
Genetics!!!
environment!!!
Describe Discontinuous variation
- Differences between individuals of a species in which each one belongs to one of a small number of distinct categories with no intermediates
- The environment has no effect on the variation
- different alleles at a single gene locus have large effects on the phenotype
- an example is blood groups; A, B, AB, or O
Describe continuous variation
- Differences between individuals of a species in which each one can lie at any point in the range between the highest and lowest values. Is regulated by multiple genes and environment
- different alleles at a single locus have small effects on the phenotype
- different genes have the same, often additive, effect on the phenotype
- A large number of genes may have a combined effect on a particular phenotypic trait; these genes are known as polygenes
describe biotic factors
these are environmental factors that are caused by living organisms e.g
- predation
- competition
- diseases
describe abiotic factors
environmental factors that are caused by non-living components e.g
- soil
- pH
- light intensity
define fitness
- the ability of an organism to survive and reproduce
define natural selection
- The process by which individuals with a particular set of alleles are more likely to survive and reproduce than those with other alleles, eventually the advantageous alleles become more frequent in the popuation.
define selection pressure
- an environmental factor that affects the chance of survival of an organism whereby an organism with a particular phenotype is more likely to survive than those with a different phenotype
describe stabilizing selection and its curve
- this is natural selection that tends to keep allele frequencies relatively constant over many generations
- the selection is against both extremes and fitness is towards the average. Normal bell curve with higher average number
describe directional selection and its graph
- natural selection that causes a gradual change in allele frequency over many generations
- the extreme trait is favoured over the others making the graph shift causing the organisms to be more fit.
describe disruptive selection and its graph
- This occurs when conditions favor both extremes of a population
- individuals at the extremes of the curve have higher fitness than the average individuals making the curve M-shaped.
what can cause directional selection
- selection pressures
- new alleles arise by mutation
describe antibiotic resistance as an example of directional selection
- when someone takes antibiotic penicillin to treat an infection, bacteria that are sensitive will die.
- however by chance there may be one or two among the population that have an allele that is resistant to the penicillin, this allele can arise by mutation.
- these bacteria will reproduce rapidly in ideal conditions
define genetic drift
- the gradual change in allele frequencies in a small population where some alleles are favoured or lost by chance and not natural selection
define gene pool
The complete set of genetic information in a population.
This process occurs in a recently isolated small population and results from only part of the gene pool being present in this small population is called ________ ______
FOUNDER EFFECT
What is an evolutionary bottleneck
- a period when the numbers of a species fall to a very low level, resulting in the loss of a large number of alleles and therefore a reduction in the species’ gene pool.
What does the Hardy-weinberg principle show
- calculation of allele frequencies
- predict how these might change in future generations
which alleles do p, p^2 and q, q^2 represent in the equations
p: dominant allele
p^2: Dominant homozygous allele
q: Recessive allele
q^2: recessive homozygous allele
The Hardy Weinburg principle cannot apply where:
- The population is too small
- Significant selective pressure against one of the genotypes
- migration of individuals that are carrying one/two alleles out of the population
- non-random mating
define artificial selection / selective breeding
The selection by humans of organisms with desirable traits to survive and reproduce
outline the steps of selective breeding
1- The population that is chosen has to show variation e.g some individuals being resistant to disease.
2- the breeder selects an individual that has the feature that can last over future generations
3- another parent will be selected showing the same variety or perhaps a different variety that can show another beneficial characteristic. The 2 chosen parents are then bred together
4. once the offspring have grown she will select the ones that show the best combination of these 2 characteristics
Define evolution
- A process leading to the formation of new species from pre-existing species over time
Define species
- A group of organisms with the same morphological, physiological, biochemical and behavioural features, which can interbreed to produce fertile offspring and are reproductively isolated from other spieces.
What are morphological features
These are structural features
What are physiological features
- These are features relating to metabolic and other processes in a living organism
what are the problems of trying to interbreed two organisms to produce a fertile offspring
- Both of the same sex
- There is no time or enough facilities to interbreed them
- they cannot breed in captivity
- Organisms that produce asexually and not sexually
- Immature and are not able to breed.
What are the features that determine whether organisms belong to the same species
- Can breed but offspring is infertile
- Genetic isolation
- DNA sequences
- Morphological features
What are the reasons for an inability to interbreed successfully
- individuals do not recognize each other as potential mates
- Animals being physically unable to mate
- incompatibility of pollen and stigma in plants
- failure of cell division in the zygote
- Offspring that soon die
- Viable but sterile offspring
Define speciation
The production of new species that can no longer interbreed with one another
What causes speciation
- Geographical barrier separates the species into 2 groups
- Where the reproductive isolation happens while the species is still living in the same place.
Describe Allopatric speciation
- This is the development of new species following geographical isolation
- Examples of geographical barriers are:
- islands
- a water body
- Over time, the morphological, physiological, and behavioural features will become different between the 2 groups. A new species will evolve
Describe sympatric speciation
- This is the development of new species without any geographical separation.
- for this to happen, the 2 groups will have to split, with one group experiencing different selection pressures compared to the other group.
- These selection pressures will force that group to adapt with new morphological and physiological features
Define ecological separation
- The separation of 2 populations because they live in different environments in the same area and so cannot breed together.
Define behavioural separation
- The separation of 2 populations because they have different behaviours which prevent them from breeding together.
Suggest ways of how DNA analysis can prove the relatability between different species
- Sources of DNA such as DNA from the mitochondria, nucleus or chloroplast can give information about the relationships between species
- The more similar DNA nucleotide sequences of 2 species are, the more closely related the specises.
- Fossil evidence such as carbon dating
- Analysis of mtDNA of different species provide evidence of their relationship
