Topic 4B: Diversity and Selection Flashcards
1
Q
What does diploid mean?
A
- 2n - 2 sets of chromosomes
- 1 from mother, 1 from father
- In normal body cells
2
Q
What does haploid mean?
A
- n - half number of chromosomes
- only from mother or father
- gametes
3
Q
What happens in a cell before meiosis 1?
A
- DNA unravels and replicates to two copies of each chromosome - chromatids
- DNA condenses - double armed chromosomes of 2 sister chromatids
4
Q
Describe meiosis 1
A
- Chromosomes arrange into homologous pairs
- Homologous pairs separate - halves number of chromosomes
5
Q
Describe meiosis 2
A
- Pairs of sister chromatids separate
- Centromeres divide
6
Q
What is produces by meiosis?
A
- Gametes
- 4 haploid daughter cells
- Genetically different
7
Q
What are the 2 ways variation occurs in meiosis?
A
- Crossing over of chromatids
- Independent segregation
8
Q
Describe crossing over of chromatids
A
- 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
9
Q
What is independent segeragtion?
A
- 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
10
Q
What is gene mutation?
A
- Change in DNA base sequence
11
Q
What is substitution?
A
- DNA base swaps
- Only affects the one triplet and so 1 amino acid
12
Q
Describe insertion
A
- Extra base added
- All move to the right
- Affects all triplets after
13
Q
How does deletion work?
A
- Base removed
- All move to the left
- Affects all triplets after
14
Q
How are mutations dangerous?
A
- 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
15
Q
Why de mutations usually not change anything?
A
- 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
16
Q
How do mutations occur?
A
- Occur spontaneously in cells
17
Q
What are mutagenic agents?
A
- Things that increase the chance of mutation or speed it up
18
Q
What are examples of mutagenic agents?
A
- Carcinogens - smoking (tar etc)
- Radiation - high energy - x rays, gamma etc
19
Q
What are chromosome mutations?
A
- When cells contain variations of number of chromosomes
- Lead to inherited conditions such as Down’s Syndrome - due to extra number 21 chromosome
20
Q
What are chromosome mutations called?
A
- chromosome non disjunction
21
Q
Define genetic diversity
A
- Number of different alleles of genes in a species or population
22
Q
Why is genetic diversity important?
A
- 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
23
Q
How can genetic diversity be increased?
A
- Mutations into new alleles
- Introduction of new alleles due to migration - gene flow
24
Q
What is a genetic bottleneck?
A
- 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
25
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
26
Describe the process of natural selection
1. Mutation causes variation and new alleles
2. A new allele has a selective advantage against a selection pressure
3. Individuals with this allele are more likely to survive and reproduce
4. They pass on the advantageous allele to the next generation
5. Over time the frequency of the allele in the population increases
27
What is an adaptation?
- Characteristic that helps an organism to survive in its environment
28
What is a behavioural adaptation?
- Way an organism acts to increase its chances of survival
29
What is a physiological adaptation?
- Processes in an organism's body that increase its chances of survival
30
What is an anatomical adaptation?
- Structural features to increase the chances of survival
31
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
32
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
33
What is stabilising selection?
- Middle trait selected for
- Extreme traits selected against
- Occurs with no environmental change
- Reduces range of characteristics
34
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
35
How is bacteria for experiments often grown?
- Liquid broth
- Distilled water, bacteria culture, nutrients
36
When testing antibiotics, what control should you use?
- Disc soaked in sterile water
37
What conditions should bacteria be incubated in?
- Lid taped on
- Stored upside down
- 25 degrees C
- 48h
38
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
39
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
