▶️ Answer/Explanation
Solution
a. ABO Blood Type Inheritance: [4]
1. Three alleles exist: IA, IB, and i ✔
2. IA and IB are co-dominant; both are dominant to i ✔
3. Genotype-phenotype relationships:
- IAIA or IAi = Blood group A ✔
- IBIB or IBi = Blood group B ✔
- IAIB = Blood group AB (co-dominance) ✔
- ii = Blood group O ✔
4. One allele inherited from each parent (Mendelian inheritance) ✔
Note: Ii notation accepted for recessive allele
b. Genetic Variation Generation: [7]
Mutation-based mechanisms:
1. DNA mutations create new alleles (e.g., base substitutions/SNPs) ✔
2. Mutagens (radiation/chemicals) increase mutation rates ✔
Meiosis-based mechanisms:
3. Crossing over creates new gene combinations ✔
4. Independent assortment of homologous chromosomes ✔
5. Random fertilization combines parental genomes ✔
Population mechanisms:
6. Natural selection favors different variants in isolated populations ✔
7. Genetic drift alters gene pools in small populations ✔
8. Horizontal gene transfer (e.g., plasmid exchange in bacteria) ✔
Disallowed: Non-substitution mutations for base changes
c. Analogous vs. Homologous Traits: [4]
Analogous traits:
1. Similar function but different evolutionary origin (e.g., bird vs. insect wings) ✔
2. Result from convergent evolution ✔
3. Cause artificial classification if used ✔
Homologous traits:
4. Similar structure from common ancestry (e.g., pentadactyl limb) ✔
5. May have different functions (e.g., whale flipper vs. human arm) ✔
6. Result from divergent evolution/adaptive radiation ✔
7. Form basis of natural classification with predictive value ✔
Question
(a) Describe what is shown in a cladogram [2]
(b) Outline how variation in organisms of the same species could lead to natural selection [3]
Answer/Explanation
a) Describe what is shown in a cladogram. [2]
- A cladogram is a diagram that shows the evolutionary relationships between different species based on shared characteristics or traits.
- The branches of the cladogram represent the common ancestors of species, with more closely related species positioned closer together. The points where branches split are called nodes, indicating a common ancestor from which different species have evolved.
(b) Outline how variation in organisms of the same species could lead to natural selection. [3]
- Genetic variation: Within a species, individuals show genetic differences due to mutations, sexual reproduction, and genetic recombination.
- Environmental pressures: These variations may make some individuals better suited to the environment, such as having traits that help them survive predators, find food, or reproduce.
- Differential survival and reproduction: Individuals with beneficial traits are more likely to survive and reproduce, passing on their advantageous traits to the next generation, leading to evolutionary changes over time.