changes in the genetic makeup of a population Flashcards
define gene
a segment of DNA coding for a particular characteristic or trait
define allele
alternative form of a gene
genotype
the alleles possessed by an organism
phenotype
the observable characteristics of an organism as a result of the interaction of its genotype with its environment
monogenic trait
a trait controlled by one gene
discontinuous variation
when there is a limited number of variations determined by a gene
locus
a specific position on a chromosome where a particular gene is located
polygenic trait
a trait controlled by multiple interacting genes
continuous variation
when a gene/s codes for a range of non-distinct variations
gene pool
the total sum of alleles found in a population
aneuploidy
the presence of an abnormal number of a particular chromosome, either trisomy or monosomy
polyploidy
a condition where an organisms has more than 2 complete sets of chromosomes
polymorphism
the presence of variations of a gene
define natural selection
the influence of environmental pressures on particular phenotypes, impacting allele frequencies within a population
define selection pressures
conditions that give organisms with certain traits a reproductive advantage over those with different traits, influencing allele frequency in a population as a result.
genetic drift
describes changes in allele frequencies in a populations as a result of random, unselective events - decreases genetic variation
what is the bottleneck effect
when a random event, such as a natural disaster, acts on a population, reducing population size and genetic variation. Offspring of surviving individuals can only inherit the remaining alleles, resulting in reduced variation .
are larger or smaller populations more effected by genetic drift
smaller
what is founder effect
the loss of genetic variation that occurs when a new population is established by a small ‘founder’ group from a larger one.
gene flow
is the movement of alleles between populations as a result of migration and interbreeding
what genetic isolation results in allopatric speciation
geographical isolation
steps in allopatric speciation
- geographical isolation, preventing gene flow between the populations
- differing selection pressures act on the populations, resulting in differing allele frequencies within the populations
- when the populations are brought back together they will be unable to produce viable offspring.
alelle frequency
the proportion of a particular allele within a population
equation for allele frequency
2(number of homozygotes) + (number of heterozygotes)
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2 (total number of individuals)
what defines different species
when they are unable to produce viable and fertile offspring
what is a mutation
a change DNA that can affect a single gene, multiple genes, or entire chromosomes
what type of mutation can be passed on
a germ-line mutation
name of a factor that induces mutation
a mutagen
2 types of point mutation
substitution and frameshift
types of substitution mutations
silent, missense (when substitution results in an amino acid replacement) and nonsense (when substitution results in a stop codon)
which has more of an effect, substitution or frameshift
frameshift as it alters every following codon.
types of block mutations
duplications (part of a chromosome is replicated), deletion mutation (part of a chromosome is removed), inversion mutations (section of DNA breaks off, rotates 180 degrees and reattaches), insertion mutations (when a section of one chromosome breaks off and reattaches to another), translocations (when segments of chromosomes are exchanged with each other)
define evolution
the change in genetic composition of populations over time
speciation
the process by which populations evolve to become distinct species
prezygotic isolating mechanisms
geographical, temporal, ecological (niche partitioning), behavioural, morphological
postzygotic isolating mechanisms
hybrid inviability (zygote dies), reduced hybrid viability (zygote survives but wont reach adulthood), hybrid sterility (cant produce offspring), and hybrid breakdown (sometimes produces offspring but they will be infertile)
what is geographical isolation
populations occupy and mate in different geographical areas (separated by a geographical barrier)
what is temporal isolation
populations mate at different times during the year
what is ecological isolation (niche partitioning)
populations occupy and mate in different ecological niches
what is behavioural isolations
populations have different courtship rituals
what is morphological isolation
when the morphological structure of organisms prevent interbreeding
what type of isolation in allopatric speciation
geographical
selective breeding
the process by which humans decide which individuals may breed based on ‘favourable’ traits
process of selective breeding:
a desirable trait is determined, parents who show trait are interbred, offspring that display trait are selected and interbed, process is continued until the population reliably reproduces the trait
detrimental effects of selective breeding
reduces resistance to environmental changes (reduced genetic variation)
reduces biodiversity
can increase abnormalities due to gene linkage
