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Codominant definition
Both alleles equally dominant and expressed in the phenotype
multiple alleles definition
More than 2 alleles for a gene
sex linkage definition
A gene whose locus is on the X chromosome
what is incomplete dominance?
- 1 allele codes for enzyme that catalyses formation of pigment
- other allele codes for other enzyme which lacks this activity so does not produce pigment
example of sex linkage
Haemophilia
what is monohybrid inheritance
The inheritance of a single gene
what does dihybrid mean
the inheritance of 2 different genes
what is the ration in dihybrid crosses
9:3:3:1
what is epistasis?
how the expression of one gene affects the phenotypic expression of another gene
example of epistasis
in mice and other mammals, coat color depends on two genes, one gene determines the pigment color (with alleles B for black and b for brown), the other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hair
what is autosomal linkage
2 Genes (characteristics) carried on the same Chromosome
why do results of genetic crossed often differ from predicted results
- random fertilisation
- independent assortment
- crossing over
how is the chi-squared test used
determines statistical difference between observed and expected frequencies
genotype definition
genetic makeup of an organism
phenotype definition
the expression of the genotype
how is sex determined genetically
Y chromosome
why are pedigree diagrams useful?
see inheritance of traits over many generations
what test do we use to compare the goodness of fit of observed phenotypic ratios with expected ratios.
chi squared
definition of autosomal linkage
two genes carried on same autosome
species exist as ___ or ____ populations
one or more
define population
a group of organisms of the same species in the same place at the same time and can interbreed
define gene pool
the range of alleles in a population
define allele frequency
how often an allele occurs in a population
What are the Hardy-Weinberg equations?
p+q=1
p^2+2pq+q^2=1
what are the conditions for the Hardy-Weinberg principle?
- no mutations arising
- large population
- no natural selection
what is p in Hardy-Weinberg
dominant allele
what is q in Hardy-Weinberg
recessive allele
what is p^2 in Hardy-Weinberg
homozygous dominant genotype
what is q^2 in Hardy-Weinberg
homozygous recessive genotype
what is 2pq in Hardy-Weinberg
heterozygous genotype
how do genetic factors lead to variation
mutations which change base sequence of amino acids
how does meiosis lead to variation
crossing over, independent assortment, random fertilisation
what are some examples of environmental factors leading to variation
climate, food, lifestyle
define evolution
the change in allele frequency in a population over time
describe natural selection in simple steps
- mutations create variation
- selection pressure e.g. competition
- organisms with favourable allele survives and reproduces, passing on allele to next generation
- allele frequency in gene pool change over many generations
define speciation
Formation of new species
when does allopatric speciation occur
geographically isolated
Describe allopatric speciation
- mutations create variation
- selection pressures
- favourable alleles survive and reproduce to pass allele to offspring
- leads to change in allele frequency
when does sympatric speciation occur
not geographically isolated
describe sympatric speciation
- mutations create variation
- causes individuals to become reproductively isolated
- temporal, behavioural and mechanical
different selection pressures operate
- leads to change in allele frequency
define the temporal mechanism
different mating seasons
define the behavioural mechanism
different courtship behaviour preventing mating
define the mechanical mechanism
incompatible genitalia
define genetic drift
change in allele frequency in a population due to chance
where does genetic drift have the strongest effect
in small populations
what is a genetic factor in evolution?
mutations
how does meiosis affect variation in phenotype?
- crossing over between homologous chromosomes
- independent segregation
- random fertilisation of gametes
define evolution
the change in allele frequency in a population over time
what causes variation in a population ?
mutations
define community
The populations of different species living in a habitat
define biotic factor
A living component of an ecosystem
define abiotic factor
non-living component of an ecosystem
define carrying capacity
max stable population size of a species that an ecosystem can support
define population
group of same species living in same place at same time
define ecological niche
the role it plays within the community
define niche competition
between 2 species when niche overlap
define ecosystem
a community and non living components of its environment
define ecology
the study of how organisms interact with one another and with their physical environment
the population size of a species can vary as a result of...
- abiotic factors
- interactions between organisms
What is intraspecific competition?
competition within a species
intraspecific competition is _______ dependent because more individuals means less _________
density, resources
What is interspecific competition?
competition between different species (occupying similar niches)
what is a predator prey example?
lynx and hare, rabbit and fox
what is succession?
the gradual change in the species that make up a community over time
what is a pioneer species?
first species to colonise and area (e.g. lichens)
what is primary succession?
plants grow where no plants have grown before
what is secondary succession?
plants grow where there has been a previous population
what happens when plants decompose?
provide the soil with nutrients
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