Section 4 - Unit 9: Genetic Diversity Flashcards
Explain why a mutation involving the deletion of a base may have a greater effect than one involving substitution of one base for another (3 marks)
- Deletion causes frame shift/alters base sequence
- Changes sequence of amino acids (from this point)
- Substitution alters one codon/one amino acid
What is meant by genetic diversity? (1 mark)
- Differences in base sequence of DNA/alleles
Describe and explain the appearance of a chromosome during meiosis (3 marks)
- Chromosome is formed of two chromatids
- Because DNA replication has occurred
- Sister chromatids held together by centromere
Name two ways in which meiosis produces genetic variation
- Independent segregation of homologous chromosomes
- Crossing over
Explain why fewer species of a plant would lead to fewer species of an animal that depends on it (3 marks)
- Fewer habitats
- So lower diversity of insects
- So fewer food sources
Suggest how you could obtain data to give a more precise value for the index of diversity of a habitat (2 marks)
- Take more samples and find mean
- Randomised sampling
What is the difference between species richness and an index of diversity (1 mark)
- Species richness only measures a number of different species (does not measure the number of individuals)
Suggest how you could decide where to take samples of a population (2 marks)
- Draw grid over area
- Select squares/coordinates at random
What two measurements are needed to calculate an index of diversity? (2 marks)
- Number of individuals of each species
- Total number of individuals / number of species
Name two ways in which meiosis produces genetic variation (2 marks)
- Independent segregation of homologous chromosomes
- Recombination by crossing over
Suggest a reason why populations might show very low levels of genetic diversity (1 mark)
- Inbreeding
Explain why an error that occurs during DNA replication is likely to be more damaging than an error that occurs during transcription? (4)
- DNA replication means errors may be inherited
- So the whole organism may be permanently affected
- Errors in transcription only affect specific cells
- So whole organism isn’t affected
Suggest using your knowledge why mules are sterile (5)
- Mules have 63 chromosomes
- Gametes are produced via meiosis
- With an odd number of chromosomes, precise pairing
- Of homologous chromosomes is impossible
- This prevents meiosis and gamete production so the mules are sterile
Define selection (1)
Process by which organisms that are better adapted to their environment survive and breed
Explain 3 differences between directional and stabilising selection (6)
- Favours phenotypes at one extreme of a population vs favours phenotypes around the mean of a population
- Changes the characteristics of a population vs preserves the characteristics of a population
- Curve remains same shape but mean shifts to left or right vs curve becomes narrower and higher but mean does not change
The principles of natural selection in the evolution of populations (4)
- Random mutation can result in new alleles of a gene.
- Many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success
- The advantageous allele is inherited by members of the next generation
- As a result, over many generations, the new allele increases in frequency in the population
Directional selection (1)
- When the environmental conditions change and the phenotypes best suited to the new conditions are more likely to survive
Example of directional selection (3)
- Antibiotic Resistance
- A single bacteria will have had a mutation meaning that it wouldn’t have been killed by an antibiotic
- Therefore, it was able to grow and populate, and the population moved to have greater penicillin resistance.
Stabilising selection (3)
- The phenotypes with successful characteristics are preserved and those of greater diversity are reduced
- If the environment stays the same then the individuals closest to the mean are favoured because they have the alleles that have given them the survival advantage
- The furthest from the mean are selected against
Example of stabilising selection (2)
- New born babies weights
- Those that have a birth weight of around 3kg are more likely to survive than those at the extremes
Explain why courtship behaviour is important for species (4)
- Recognise members of their own species
- Synchronise mating
- Form a pair bond
- Become able to breed
State four ways in which you could investigate the genetic diversity between species (4)
- The frequency of measurable or observable characteristics
- The base sequence of DNA
- The base sequence of mRNA
- The amino acid sequence of the proteins encoded by DNA and mRNA
Describe the process of crossing over and explain how it increases genetic diversity (4 marks)
- Homologous pairs of chromosomes associate
- Chiasma(ta) form
- (Equal) lengths of chromatids/alleles are exchanged
- New combinations of alleles
Explain why scientists can use protein structure to investigate the evolutionary relationships between different species (2 marks)
- Closer the amino acid sequence, the closer the relationship
- Protein structure related to base sequence
Explain why comparing the base sequence of genes provides more evolutionary information than comparing the structure of proteins (2 marks)
- Base triplets longer / more bases than amino acids
- Introns also available
