Chapter 17- Selection and Evolution Flashcards
(37 cards)
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
