Topic 4B: Diversity and Selection Flashcards
What does diploid mean?
- 2n - 2 sets of chromosomes
- 1 from mother, 1 from father
- In normal body cells
What does haploid mean?
- n - half number of chromosomes
- only from mother or father
- gametes
What happens in a cell before meiosis 1?
- DNA unravels and replicates to two copies of each chromosome - chromatids
- DNA condenses - double armed chromosomes of 2 sister chromatids
Describe meiosis 1
- Chromosomes arrange into homologous pairs
- Homologous pairs separate - halves number of chromosomes
Describe meiosis 2
- Pairs of sister chromatids separate
- Centromeres divide
What is produces by meiosis?
- Gametes
- 4 haploid daughter cells
- Genetically different
What are the 2 ways variation occurs in meiosis?
- Crossing over of chromatids
- Independent segregation
Describe crossing over of chromatids
- In meiosis 1 homologous chromosomes line up
- Chromatids twist around each other and bits swap over
- Chromatids then have the same genes but a different allele combination
What is independent segeragtion?
- Homologous pairs line up
- When separated in meiosis 1 - random combination given to daughter cells - have completely different combinations
- Shuffling of chromosomes gives genetic variation
What is gene mutation?
- Change in DNA base sequence
What is substitution?
- DNA base swaps
- Only affects the one triplet and so 1 amino acid
Describe insertion
- Extra base added
- All move to the right
- Affects all triplets after
How does deletion work?
- Base removed
- All move to the left
- Affects all triplets after
How are mutations dangerous?
- Can change the amino acid coded for
- Changes polypeptide chain
- Can change shape of protein produced and stop its function
- Can change it to be a stop codon and prevent polypeptide being produced at all
Why de mutations usually not change anything?
- Mutations often occur in non coding regions
- DNA is degenerate so despite the change, the same amino acid is still coded for
- Even if an amino acid changes, small difference and protein can still function - especially with substitutions
How do mutations occur?
- Occur spontaneously in cells
What are mutagenic agents?
- Things that increase the chance of mutation or speed it up
What are examples of mutagenic agents?
- Carcinogens - smoking (tar etc)
- Radiation - high energy - x rays, gamma etc
What are chromosome mutations?
- When cells contain variations of number of chromosomes
- Lead to inherited conditions such as Down’s Syndrome - due to extra number 21 chromosome
What are chromosome mutations called?
- chromosome non disjunction
Define genetic diversity
- Number of different alleles of genes in a species or population
Why is genetic diversity important?
- If it is low - populations cannot adapt to a change in the environment
- Could all be wiped out by one event e.g. a disease
How can genetic diversity be increased?
- Mutations into new alleles
- Introduction of new alleles due to migration - gene flow
What is a genetic bottleneck?
- Something causes a large population reduction (disease, disaster etc)
- Reduces the number of alleles in the gene pool
- Survivors reproduce to a larger population using the old individuals
What is the founder effect?
- A few organisms move from the population to form a new colony
- Frequency of alleles in the new population can be very different to the original e.g. a very rare allele in the original population can be very frequent in the new colony
Describe the process of natural selection
- Mutation causes variation and new alleles
- A new allele has a selective advantage against a selection pressure
- Individuals with this allele are more likely to survive and reproduce
- They pass on the advantageous allele to the next generation
- Over time the frequency of the allele in the population increases
What is an adaptation?
- Characteristic that helps an organism to survive in its environment
What is a behavioural adaptation?
- Way an organism acts to increase its chances of survival
What is a physiological adaptation?
- Processes in an organism’s body that increase its chances of survival
What is an anatomical adaptation?
- Structural features to increase the chances of survival
What is directional selection?
- One extreme trait is selected for
- Other extreme and middle are selected against
- Can be a response to an change in environment
What is an example of directional selection and how does it work?
- Antibiotic resistance
- Some bacteria have alleles for antibiotic resistance
- When exposed to antibiotic, those without resistance alleles die
- Resistant survive, reproduce without competition and pass on resistance allele
- Over time, most in the population have this allele
What is stabilising selection?
- Middle trait selected for
- Extreme traits selected against
- Occurs with no environmental change
- Reduces range of characteristics
What is an example of stabilising selection and how does it work?
- Human birth weights
- Small babies less likely to survive - hard to maintain body temperature
- Large babies less likely to survive as they are hard to give birth to
- Middle sized babies are most favourable so weight off babies shifts to the middle
How is bacteria for experiments often grown?
- Liquid broth
- Distilled water, bacteria culture, nutrients
When testing antibiotics, what control should you use?
- Disc soaked in sterile water
What conditions should bacteria be incubated in?
- Lid taped on
- Stored upside down
- 25 degrees C
- 48h
Why is an aseptic technique needed?
- Prevent contamination of cultures by unwanted microbes –> could affect growth of microorganism you are investigating
- Avoid contamination with microorganisms that could cause harm / illness
What aseptic techniques should be used?
- Regularly disinfect work surfaces
- Don’t put utensils on work surface
- Put contaminated utensils in a beaker of disinfectant
- Use sterile equipment - glass cleaned in autoclave, use ethanol, bunsen flame
- Work near a bunsen burner - upward motion of hot air - draws microbes away
- Minimise time of lid foo petri dish / only open part way to prevent contamination from the air
- Flame neck of culture bottle - when opened and after use
- Wash hands before and after
