Lecture 3 Flashcards
Gene
a unit of heritable DNA
Allele
a variant of a gene
Locus
a location on a chromosome
Gene pool
the total aggregate of genes in a population at any one time, all copies of all alleles of all genes at all loci
Variation
-for evolution to happen heritable genetic and phenotypic variation must exist
-variation may mean that some population members have alleles that are absent in others
-variation may also mean combinations of different traits that are not present in other members
mutation
-changes in the nucleotide sequence of DNA
-a key mechanism in producing variation
-can cause new alleles and genes to arise
production of genetic variation
mutation
sexual reproduction
how does sexual reproduction produce variation
new combinations of genes produced
recombination- exchange of DNA between chromosomes (e.g crossing over)
mutation definition
a change in an organisms nucleotide sequence that can result from copying errors during DNA replication
Heritable mutations
mutations that occur in the germline (the cell population that produces gametes)
-consequently random variation occurs in gametes
Point mutations
a change in one base in a gene
-may have no functional effect
-but if function is affected, a point mutation can have a large impact on phenotype
mutation rates in animals and plants
tend to be relatively low
-sperm contributes to 130/140 mutations while the egg only 10
fitness effects of mutations
some are harmful causing organisms to become subject to natural selection (deleterious)
some may be selectively advantageous and also become subject to natural selection (beneficial)
some have no effect
microorganism mutation rate
much faster than animals or plants
population
a localised group of interbreeding individuals that are:
-all from one species
-are reproductively connected
-have overlapping geographic ranges
microevolution
change below species level, the smallest scale of evolution
Macroevolution
change that occurs above the species level (typically described within phylogenies)
Genetic drift
-the 1st mechanism of microevolution
-a change in the frequency of alleles due to random sampling of organisms
-genetic drift tends to reduce variation through loss of alleles
Bottleneck effect
change in allele frequencies when a population drops in size
-e.g natural disaster
-some alleles will be less frequent/ not exist altogether
-new allele frequencies may vary greatly
Founder effect
-change in allele frequencies when a new population splits off from another
-occurs when a few individuals become isolated from the rest of the population
-allele frequencies in isolated pop are different to rest of pop
Impacts of the founder effect
conservation- founder effects on population alleles may affect viability of captive bred zoo populations
Disease- founder effects on small populations may increase the frequency of harmful alleles
Gene flow
gene flow is the movement of alleles among populations
-tends to homogenise the genetic makeup of different populations
-gene flow can increase the fitness of a population
-but gene flow could sometimes decrease the fitness of a population
Introgression
transfer of an alleles from one species to another species
-introgressed genes can have important disease effects
Natural selection
the 3rd mechanism of microevolution
-it filters variation between individuals to select phenotypes
-the only one that consistently changed allele frequencies and causes consistent adaptive selection
