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gene control
transcription of genes is controlled by transcription factors. They are proteins that bind to specific DNA sequences and control the flow of information from DNA to RNA by controlling mRNA formation.
structural genes
codes for structural protein/enzymes/rRNA (anything other than a transcription factor) These proteins are needed for the cellular structure and function of the cell.
Regulatory genes
codes for proteins that control gene expression/transcription. for example, transcription factors/ DNA binding protein. Binds to promotor/ operator/ DNA response element. Stops and allows RNA polymerase to bind to DNA.
Repressors
proteins due/ to coded by regulatory genes that bind to repressible enzymes on the operator on a bacteria’s DNA to prevent its synthesis.
Inducers
synthesis of an inducible enzyme only occurs when its substrate is present. Transcription of the gene occurs as a result of an inducer (the substrate) interacting with the protein produced by the regulatory gene e.g. B-galactosidase is an inducible enzyme
role of gibberellin in the germination of Barley
DELLA proteins inhibit germination
seeds absorb water
stimulating the production of gibberellin which causes the breakdown of DELLA proteins
leads to the transcription of mRNA coding for amylase
in the aleurone layer
Amylase causes hydrolysis of starch to maltose
maltose is then converted to glucose, which is respired by embryo during germination
discontinuous variation
different alleles at a single gene locus have a large effect on the phenotypes. Different alleles have a different effect on the phenotype, causing clearly distinguishable characteristics.
continuous variation
different alleles have a small effect on phenotypes. A large number of alleles combine to give an additive effect on the phenotypic trait (called polygenes). The measurements can lie anywhere between two extremes.
There are some environmental effects due to phenotypes, this includes their nutrition and exposure to chemicals along with their genetic contribution.
yes
Natural selection
a large, population, where they can potentially overproduce, and yet a genetically diverse population (where not every organism has the same alleles/ features) There is an increased chance of survival and reproduction of organisms with a particular phenotype because they are better adapted to the environment. They pass on their beneficial allele, so this allele frequency increases in the population
Stabilizing selection
a stable environment where the conditions remain the same, alleles are continuously passed on in successive generations. The extreme phenotypes are selected against and middle phenotypes are best adapted to survive
directional/evolutionary selection
a change in environmental conditions, creating a selection pressure, original phenotype selected against. Allele frequency changes, favoring the more extreme phenotypes.
genetic drift: the founder effect
Random change in the genepool, where the allele frequency changes because only some individuals in the population reproduce
disruptive selection
extreme phenotypes are favoured and selected for. slection results in two distinct phenotypes
Conditions for the Hardy Weinberg principle
population is large
there is random mating between the individuals in the populations
there are significant selection pressures that give particular phenotypes an advantage
no new mutations
no introduction of alleles by immigration
all genotypes are equally fertile