2.2 Evolution Flashcards
Define Evolution
Evolution is the change over time in the proportion of individuals in a population differing in one or more inherited traits
How do changes in alelles frequency occur in evolution
Through the non-random processes of natural selection and sexual selection, and the random process of genetic drift
Natural selection acts on
Genetically varied populations
Variation arises as a result of
Mutations
Describe mutations
Mutation is the original source of
new sequences of DNA. These new
sequences can be novel alleles. Most mutations are harmful or neutral, but in rare cases they may be beneficial to the fitness of
an individual.
Talk about populations offspring in regards of the environment
Populations produce more offspring than the
environment can support
Individuals with variations that are better suited to their environment tend to……
- survive longer
- produce more offspring
- breed to pass on those alleles that conferred an advantage to the next generation
What is the result of selection
Selection results in the non-random increase
in the frequency of advantageous alleles and
the non-random decrease in the frequency of
deleterious alleles.
Define sexual selection
Sexual selection is the non-random process
involving the selection of alleles that increase
the individual’s chances of mating and
producing offspring
Sexual selection may lead to….
sexual dimorphism
Sexual selection can be due to
- Male to Male Rivalry
- Female Choice
Describe male to male rivalry
Male-male rivalry: large size or weaponry
increases access to females through conflict.
Define Female Choice
Female choice involves females assessing
the fitness of males.
When does genetic drift occur
Genetic drift occurs when chance events
cause unpredictable fluctuations in allele
frequencies from one generation to the next
What type of population is genetic drift more important in and why
Genetic drift is more important in small
populations, as alleles are more likely to be
lost from the gene pool
Describe population bottlenecks
Population bottlenecks occur when a
population size is reduced for at least one
generation.
Describe Founders Affect
Founder effects occur through the isolation of
a few members of a population from a larger
population. The gene pool of the new
population is not representative of that in the
original gene pool.
Why is the gene pool altered by genetic drift?
A gene pool is altered by genetic drift
because certain alleles may be underrepresented or over-represented and allele
frequencies change
Where selection pressures are strong, the rate of evolution can be _________
Rapid
Define Selection Pressures
Selection pressures are the environmental
factors that influence which individuals in a
population pass on their alleles.
Selection pressures can be sorted into two categories
Biotic
- competition
- predation
- disease
- parasitism
Abiotic
- changes in temperature
- changes in light
- changes in humidity
- changes in pH
- changes in salinity
The Hardy-Weinberg (HW) principle states
that
In the absence of evolutionary
influences, allele and genotype frequencies
in a population will remain constant over the
generations
The conditions for maintaining the HW
equilibrium are:
no natural selection, random
mating, no mutation, large population size
and no gene flow (through migration, in or
out).
The HW principle can be used to
determine
whether a change in allele frequency is
occurring in a population over time
HW Equation and what it stands for
p^2 + 2pq + q^2 = 1
p = frequency of dominant allele
q = frequency of recessive allele
p^2 = frequency of homozygous dominant genotype
2pq = frequency of heterozygous genotype
q^2 = frequency of homozygous recessive
genotype
Changes in HW suggest
evolution is occurring
Define Fitness
Fitness is an indication of an individual’s
ability to be successful at surviving and
reproducing
Fitness is a measure of the tendency of some
organisms to produce more surviving
offspring than competing members of the
same species.
Relation of fitness and the gene pool of the next generation
It refers to the contribution made to the gene
pool of the next generation by individual
genotypes
Two categories of fitness
- Absolute Fitness
- Relative fitness
Define absolute fitness
Absolute fitness is the ratio between the
frequency of individuals of a particular
genotype after selection, to those before
selection
Absolute fitness Equation
frequency of a particular genotype
after selection
÷
frequency of a particular genotype
before selection
Absolute fitness in relation to the values obtained from the equation
If the absolute fitness is 1, then the frequency
of that genotype is stable. A value greater
than 1 conveys an increase in the genotype
and a value less than 1 conveys a decrease.
Define Relative Fitness
Relative fitness is the ratio of the number of
surviving offspring per individual of a
particular genotype to the number of
surviving offspring per individual of the most
successful genotype
Relative fitness equation
number of surviving offspring per
individual of a particular genotype
÷
number of surviving offspring per
individual of the most successful genotype
Define co-evolution
Co-evolution is the process by which two or
more species evolve in response to selection
pressures imposed by each other
How does a change in traits of one species affect another
A change in the traits of one species acts as
a selection pressure on the other species
Co-evolution is frequently seen in pairs of
species that have __________
symbiotic interactions
Define Symbiosis
co-evolved intimate relationships
between members of two different species.
Define Mutualism
Mutualism: both organisms in the interaction
are interdependent on each other for
resources or other services. As both
organisms gain from the relationship, the
interaction is (+/+).
Define Commensalism
Commensalism: only one of the organisms
benefits (+/0).
Define Parasitism
Parasitism: the parasite benefits in terms of
energy or nutrients and the host is harmed as
the result of the loss of these resources (+/-).
The red queen hypothesis states that……
in a
co-evolutionary relationship, change in the
traits of one species can act as a selection
pressure on the other species
Species in co-evolutionary species must
Adapt to avoid extinction
