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
Selective breeding
Artificial selection is done by humans, repeatedly, where the allele frequency increases.
reasons for artificial selection
we can select for Docility (easy to handle)
disease resistance
high yield
uniformity
the consequence of selected groups
inbreeding depression/ lack of hybrid vigor
increased homozygosity, uniformity in produce can be wiped by diseases
more chance a harmful allele may be expressed
less genetic variation
How speciation/ evolution has occurred
there is no gene flow between 2 populations
gene mutations occur
there is a change in chromosome number
so a change in the gene pool or allele frequency
different selection pressures due to different environmental conditions
genetic drift, which is a random factor may be the cause
allopatric speciation where the population is geographically isolated
advantageous alleles are selected for
they can no longer interbreed
when 2 species are brought back together
number of species initially may increase because of more variety of food and more space
competition happens between species
possible reduction in the number
selection pressure may select for certain alleles
Mitochondrial clock
Mitochondria contain a single DNA molecule that is passed down the female line. Analysis of the mtDNA can be used to determine how closely related two different species are. the more similar the sequence the more closely related.
Animo acid sequence in evolution
certain proteins can be used, such as the B-globin chain or the electron transport chain, found in a number of organisms suggesting they originated from a common ancestor.
Allopatric speciation
group of individuals that are geographically isolated from the rest. overtime, the allele frequency changes so much they can no longer interbreed to produce fertile offspring
Sympatric speciation
two groups of individuals live in the same area may become unable to interbreed: mainly due to
courtship behaviors changes
or they live in different habitats of the same area
or due to temporal reasons
or genetic drift
These factors can be classified as prezygotic or postzygotic behaviors.
Artificial selection
Humans Parents with desirable traits Example Bred/crossed Select offspring with desirable features Repeated for many generations Increase in frequency of desired alleles/decrease in frequency of undesired alleles Inbreeding depression/ loss of vigour May occur