Variation and Natural Selection
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Variation and Natural Selection
Checkpoints content review questions
What is meant by variation when looking at members of a population?
differences between organisms
We lok for
that is of interest in a population
List and briefly describe the 4 main groups of variation
are the variations that are seen physically
are differences in how an individual's body functions
are the differering abilities to produced biochemical molecules (enzymes)
are the different behavious (right handed, left handed, mating calls)
What are the two major causes of variation?
, there is a range of alleles for most genes, alleles inherited give a certain genetic potential (eg - having the pigments for tan skin)
can affect genetic inheritance (eg - living in a sunny environment for your skin to tan)
differences in genes are the basis of variation, but their expression is altered by changing internal and external environmental influences
What is the difference between genotypic variation and phenotypic variation?
is variation in the types of alleles inherited.
is variation in the traits displayed by an individual. Internal functioning and biochemistry are also aspects of phenotype
Do individuals with the same genotype have the same phenotype?
No, individuals with the same genotype do not always have the same phenotype as the
can affect the expression of the genes inherited
Do individuals with the same phenotype have the same genotype?
No, this is because individuals who show a dominant phenotype can be heterozygous or homozygous for the alleles responsible
Explain monogenic and discontinuous variation
Characteristics determined by one gene are monogenic
As the phenotypes fall into discrete groups, the variation is described as being discontinuous
eg - ABO blood types
Explain polygenic and continuous variation
Characteristics determined by a number of genes, each at different locus of different chromosomes
As the phenotypes do not fall into discrete groups, it is said to be continuous
Can be represented by a bell curve
Eg - weight of the population
List the sources of variation (6)
- introduces new alleles
- change in size and number
Crossing over and recombination
- shuffles the paternal and maternal alleles within a homologous pair of chromosomes
Independant assortment of chromosomes
- allows different combinations of alleles to be formed in the resulting gametes
- different mates provide different alleles
- many are produced but few are selected for fertilization
Which is a more important source of variation - Mutation or recombination?
is a more important source because it gives rise to
of alleles is also important because it shuffles the alleles into new combinations
ALthough there is no additional variation, the new combination of alleles could lead to a better set of characterisitic in offspring
How are evolution and natural selection related?
Evolution occurs as the result of natural selection
evolution refers to the changes in species over time
natural selection is the process that aids the change
What must exist in a population for natural selection to occur?
must exist in the popution
if all individuals have the same phenotype, selection for the better suited phenotype wouldn't occur
Is selection at a phenotypic or genotypic level?
Natural selection occurs at the
individuals with the better suited phenotype will have a selective advantage in their environment
less well suited individuals tend not to survive and reproduce
How does natural selection affect allele frequency?
As phenotype is largely determined by genotype, alleles that code for the better suited phenotypes will become more common
Does the biological fitness of an individual vary? If so, what determines as individual's fitness?
Determined by the varying environemnts
eg - Polar bear is biologically fitter in the Artic circle, not in the Simpson desert
Which individuals are more likely to survive in a particular environment?
Individuals who have the phenotypes that better suit the environment
Which individuals are more likely to reproduce in a particular envirnoemtn?
Individuals that are well adapted to their environment
poorly suited individuals are less likely to survive and reproduce
If they do, they would produce less offspring
How long must an individual live in order to pass on their alleles (genetic information) to the next generation?
Live long enough to
Gene pool and allele frequency
of a population is the total availble alleles present in the population.
over a numebr of generations, the alleles that give individuals an advantage will increase in frequency in the gene pool
Difference between natural and artificial selection
both result in evolutionary change
What is the most important test to distinguish different species?
Test to see whether individuals can mate and produce viable and fertile offsping
Features of static gene pools
equal fitness of allelles
no natural selection
no gene flow
large population size
Define allele frequency
The relative number of an allele in a population
doesn't depend on whether its expression in phenotype is dominant or recessive
What causes shifts in allele frequencies?
recombinatino and mating by change
different slections of phenotypes in a population
Movement out of the population
movement into the population
Define genetic drift
The change in the frequencies of alleles in a population due to change
Trait controllled by a polygene
polygene are a group of genes at more than one locus, that cumulatively affect the overall expression of one phenotype, causing a continuous variation in that charateristic
Factors provided by the environment that act to favour one phenotype over another
List the kinds of selecting agent/pressures
may be an aspect of the physical environment - climate, chemical composition, moisture levels
may be the influence of another species - predation or parasitism
may be population pressure and the competition from members of the same species
a process occuring in a particular environment that selects individuals with better suited phenotypes to survive and reproduce and those without it to decline in number
can be articial or natural
The selection of organisms with desirable phnotypes for slective bredding to produce individuals with speficic charaterists
when humans increase the frequency of alleles that code for the desirable traits over generations
Record books that show genetic relationships betwween individuals considere as potential breeding stock
used in commercial artificial selection and breeding programs for endangered species
The movement of alleles in between populations due to migration of individuals
A group of organisms of the same species living at a point of time in a particular area
A group of organisms that can mate and reproduce viable and fertile offspring
The process that leads to a new species
variation exist within a population
Gergraphical barrier seperates the initial population so there is no
Different selection pressures =
different natural selection
which selecs for different alleles
in small populations creates diffeernt combinatinos of alleles in the 2 populations
the populations become so different
arises in one population which means that polutaions can
no longer mate to produce viable fertile offspring