genetic diversity and adaptation Flashcards
continuous variation
The characteristic / trait occupies a range of values.
Eg. IQ, Weight, Height.
Graph is drawn using histograms / line.
Determined by many genes (polygenic characteristics), with each gene having multiple alleles (multiple allele inheritance).
More influenced by the environment.
discrete / discontinuous variation
The characteristic / trait falls into categories.
Eg. Blood groups (A, B, AB & O).
Graph is drawn using bars.
Determined by one gene (monogenic characteristics), rarely by two genes; such genes have two alleles (rarely three alleles).
Less influenced by the environment.
natural selection
Darwin’s theory of evolution was based on two basic observations:
1. Organisms over-reproduce. 2. Yet population sizes remain the same. 1. Individuals of a population show variation. (Variation in the population due to mutations.) 2. The environment exerts selection pressure. 3. Some individuals are better adapted to the environment than others, because of the advantageous alleles they have. 4. These individuals survive, reproduce and pass on the beneficial / advantageous alleles to their offspring. 5. When repeated over many generations, the frequency of the advantageous alleles will increase in the population. 6. This is an example of stabilising OR directional OR disruptive selection.
three types of selection
Three types:
1. Stabilising selection - organisms with the mean value are selected for - both extremes are selected against so mean remains the same and SD decreases 2. Directional selection - one extreme is selected for while other extreme is selected against so new mean value 3. Disruptive selection - both extremes are selected for and the mean is selected against - 2 new populations are formed - one with higher mean and one with lower mean than before
antibiotic resistance in bacteria
An antibiotic is a molecule that prevents growth of bacteria.
Antibiotics are used to treat bacterial diseases in humans and in animals.
Applying / using the antibiotic is the selection pressure, the allele for resistance to the antibiotic is selected for (directional selection).
Excessive use of antibiotics has led to antibiotic-resistant bacteria (eg. MRSA), ie very difficult to treat diseases.
Mechanisms by which antibiotics work: ONLY WORK ON PROKARYOTES.
1. Inhibit synthesis of peptidoglycan cell wall. (eg. Penicillin)
2. Inhibit DNA Replication by binding to a bacterial enzyme needed for rep (eg. Nalidixic acid)
3. Inhibit Transcription by binding to bacterial RNA Polymerase. (eg. Rifampicin)
4. Inhibit Translation by binding to 70S ribosomes. (eg. Tetracycline)
5. Inhibit the lipids associated with the bacterial cell wall - discovered in 2012. (eg. Teixobactin)
All the above only inhibit prokaryotic mechanisms, therefore can be prescribed to animals without harmful effects.
Ineffective against virus.
Ineffective against fungal cells.
maintaining aseptic conditions - why
Maintaining aseptic conditions: (Why)
1. Prevent bacteria from the environment contaminating the experiment:
a. bacteria from the envt might be resistant to a particular antibiotic, whereas the experimental bacteria might be sensitive (or vice versa) - recording false positive or false negative results.
b. competition for nutrients, oxygen, etc.
2. Prevent bacteria from the experiment contaminating the environment
a. Bacteria might be pathogenic (especially hospital samples, etc)
b. Bacteria might exchange antibiotic resistance genes with pathogenic bacteria in the environment.
maintaining aseptic conditions - how
Maintaining aseptic conditions: (How)
1. Autoclave (heat at high temperature and high pressure) all glassware and nutrient medium. 2. Work in a positive pressure cupboard (like a fume hood). 3. Wipe work surfaces with ethanol before and after the experiment. 4. Work close to a bunsen burner flame / work in the updraft of a flame. 5. Flame the mouth of tubes / flasks and spreaders. 6. Partially open petri dishes when applying the bacteria (don't leave them open for a long time). 7. Discard all used pipettes etc into disinfectant solution. 8. At the end of the experiment, all bacterial cultures, plates etc are autoclaved to kill the bacteria before discarding.
what is a mutation
an alteration to the DNA base sequence
often arise spontaneously during DNA replication
why might a mutation not lead to a change in the amino acid sequence
genetic code is degenerate so mutation may end up coding for same amino acid as the original triplet
mutation may occur in intron
what is a substitution mutation
when a nucleotide in the DNA sequence is replaced by another
this is more likely to be a quiet mutation meaning no change occurs in the amino acid sequence
what is a deletion mutation
when a nucleotide in the DNA sequence is lost
this is more likely to be harmful and significant as it leads to a frame shift which means that the entire amino acid sequence will be different
what is a mutagenic agent
factors that increase the rate of gene mutation
eg x-rays, UV light, chemicals in eg tobacco
what is a polyploidy chromosome mutation
where an individual has three or more sets of chromosomes instead of two
what is chromosome non-disjunction
when chromosomes fail to separate correctly in meiosis
resulting in gametes with one more or less chromosome than normal
PMT what is meiosis
a form of cell division that produces four genetically different haploid cells (cells with half the number of chromosomes found in the parent cell) known as gametes
how does meiosis differ from mitosis
meiosis produces four genetically different cells with half the number of chromosomes as the parent cell
mitosis produces two genetically identical cells with the same number of chromosomes as the parent cells
what happens during meiosis 1
homologous chromosomes pair to form bivalents
crossing over (exchange of sections of genetic material) occurs at chiasmata
cell divides into two - homologous chromosomes separate randomly - each cell contains either maternal or paternal copy
what happens during meiosis 2
independent segregation of sister chromatids
each cell divides again, producing 4 haploid cells
in which two ways does meiosis produce genetic variation
crossing over during meiosis 1
independent assortment (random segregation) of homologous chromosomes and sister chromatids
result in new combination of alleles
define population
all the organisms of a particular species that live in the same place
what is an allele
different forms of a particular gene, found at the same locus (position) on a chromosome
a single gene could have many alleles
define genetic diversity
the total number of different alleles in a population
what advantage does a high genetic diversity provide
ability to adapt to a change in environment; allows natural selection to occur
explain how natural selection results in development of new characteristics
random mutations result in new alleles
some alleles provide an advantage, making an individual more likely to survive and reproduce
their offspring receive the new allele, and frequency continues to increase over many generations
