Genetics and Populations Flashcards
abiotic factors
The non-living aspects of an ecosystem e.g. temperature, light intensity, moisture, soil pH and oxygen levels.
adaptation
a feature of an organism that increases its chance of survival in its environment.
allele
a version of a gene
allele frequency
The number of times an allele appears within a population’s gene pool.
allopatric speciation
A form of speciation that occurs when two populations become geographically isolated.
autosomal linkage
When two or more genes are positioned on the same autosome. They are unlikely to be separated by crossing over during meiosis so are often inherited together.
autosome
a chromosome that is not an X or Y chromosome
belt transect
A line along a sampled area, upon which quadrats are placed at certain
intervals to determine the abundance and distribution of organisms in an ecosystem.
biodiversity
The variety of genes, species and habitats within a particular area.
biotic factors
The living components of an ecosystem e.g. food availability, pathogens and predators.
carrying capacity
The average size of a population that can be supported by an ecosystem over extended periods of time. This varies depending on biotic and abiotic factors.
chi-squared test
A statistical test used to determine whether a pattern of inheritance is statistically significant.
climax community
The stable community of organisms that exists at the final stage of ecological succession.
codominant
when both alleles for a gene in heterozygous organisms equally contribute to the phenotype
community
all of the populations of different species living together in a habitat
conservation
The maintenance of ecosystems and biodiversity by humans in order to preserve the Earth’s resources. This typically involves the management of succession.
degrees of freedom
the number of categories minus one
dihybrid inheritance
The inheritance of two different genes, that determine two
phenotypes, on two different chromosomes.
diploid
Describes a cell with a nucleus containing two sets of chromosomes.
directional selection
A type of selection that favours one extreme phenotype and selects against all other phenotypes.
disruptive selection
A type of selection that favours individuals with extreme phenotypes and selects against those with phenotypes close to the mean.
dominant
Describes an allele that is always expressed. Represented by a capital letter.
ecosystem
The community of organisms (biotic) and non-living (abiotic) components of an
area and their interactions. It is a dynamic system.
epistasis
Describes a relationship between genes where the allele of one gene affects the expression of a different gene.
evolution
The gradual change in the allele frequencies within a population over time. Occurs due to natural selection.
gene
A length of DNA on a chromosome that codes for the production of one or more polypeptide chains and functional RNA.
gene pool
All of the different versions of genes (alleles) in the individuals that make up a population.
genetic drift
variations in allele frequencies in small populations due to chance
genetic variation
Differences in genotypes between members of a population which may
occur due to mutations, meiosis, or random fertilisation.
genotype
an organism’s genetic composition (describes all alleles)
habitat
the region where an organism normally lives
hardy-weinberg principle
A model that predicts that the ratio of dominant and recessive alleles in a population will remain constant between generations if the following five conditions are met: no new mutations; no natural selection; no migration; large population; and random mating. It provides an equation for calculating the frequencies of alleles:
p2 + 2pq + q2 = 1.0
where p is the frequency of the dominant allele, and q is the frequency of the recessive allele.
heterozygous
When someone has two different alleles of a gene e.g. Ff.
homozygous
When someone has two identical alleles of a gene e.g. ff.
interspecific competition
A type of competition that takes place between members of different species.
intraspecific competition
A type of competition that takes place between members of the same species.
locus
the position of a gene on a chromosome
mark-release-recapture
A method of estimating the population size of motile organisms. It involves capturing a sample of the population, marking them and releasing them. At a later date, another sample is captured and the number of marked individuals recorded.
monohybrid inheritance
the inheritance of one gene
multiple alleles
when a gene has more than two potential alleles
natural selection
The process by which the frequency of beneficial alleles gradually increases in a population’s gene pool over time. This theory was developed by Charles Darwin.
niche
Describes how an organism ‘fits’ into an ecosystem and its role in that environment.
phenotype
An organism’s observable characteristics. Due to interactions of the genotype
and the environment.
pioneer species
Species that can survive in hostile environments and colonise bare rock or sand e.g. lichens.
population
All organisms of the same species living with one another in a habitat at the same time.
predator
an organism that eats other organisms
prey
an organism that is eaten by predators
quadrat
A square grid of a known area used in sampling to determine the abundance of organisms in a habitat. There are two types: point quadrats and frame quadrats.
random sampling
A sampling technique used to avoid bias e.g. creating a square grid and generating random coordinates.
recessive
Describes an allele that is only expressed in the absence of a dominant allele. Represented by a small letter.
selection pressures
Environmental factors that drive evolution by natural selection and limit population sizes e.g. competition, predation and disease.
sex-linkage
the presence of a gene on an X or Y chromosome
speciation
The formation of new species due to the evolution of two reproductively
separated populations. Two forms: allopatric and sympatric speciation.
species
A group of similar organisms that are able to breed with one another to produce living, fertile offspring.
stabilising selection
A type of selection that favours individuals with phenotypes close to the mean (average) and selects against extreme phenotypes.
succession
Describes changes in the community of organisms occupying a certain area over time.
sustainable
the ability to maintain something for future generations
sympatric speciation
A form of speciation that occurs when two populations within the
same area become reproductively isolated.
systematic sampling
A sampling technique used to determine the abundance and distribution of organisms along an area at periodic intervals e.g. along a belt transect. This is commonly used in ecosystems where some form of gradual change occurs.
variation
the differences between individuals due to genes, the environment, or a combination of both
