Question
▶️Answer/Explanation
a. Describe the inheritance of red-green colour blindness. [3]
- Red-green colour blindness is a sex-linked recessive trait carried on the X chromosome.
- Males (XY) will be colour blind if they inherit the allele from their mother since they have only one X chromosome.
- Females (XX) need two copies of the allele (one from each parent) to express the condition, making them less likely to be affected but able to be carriers.
b. Outline the causes of variation in one example of continuous variation in humans. [5]
Example: Human height
- Genetic factors: Multiple genes contribute to height, resulting in a wide range of possible heights.
- Environmental factors: Nutrition, health, and exercise during development influence final height.
- Gene-environment interaction: The combination of genetic potential and environmental influences determines the actual height.
c. Explain how evolution occurs and which factors can cause the process to be rapid. [7]
- Variation: Genetic variation in a population, caused by mutations, recombination, and gene flow.
- Natural selection: Traits that increase survival and reproduction become more common over generations.
- Genetic drift: Random changes in allele frequencies, especially in small populations.
- Gene flow: Movement of genes between populations due to migration.
- Speciation: Accumulation of changes leads to the formation of new species.
- Factors for rapid evolution:
- Large mutations provide strong advantages quickly.
- Small populations experience faster genetic drift.
- Environmental changes favor certain traits, accelerating selection.
- Short generation times allow more generations to evolve rapidly.
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Question
Evolution causes gene pools to change over time and new species to be formed.
(a) Outline how adaptive radiation provides evidence for evolution. [3]
(b) Describe polyploidy and how it can lead to speciation. [5]
(c) Explain how a newly discovered plant species would be classified and named. [7]
Answer/Explanation
(a) Outline how adaptive radiation provides evidence for evolution. [3]
- Rapid diversification: Adaptive radiation occurs when one species rapidly evolves into many species, each adapted to different environments.
- Common ancestor: All the species involved share a common ancestor, showing how evolution leads to species diversification.
- Natural selection: The development of specific traits in each species demonstrates the role of natural selection in evolution.
(b) Describe polyploidy and how it can lead to speciation. [5]
- Polyploidy is when an organism has more than two sets of chromosomes.
- Autopolyploidy: Chromosome duplication within the same species.
- Allopolyploidy: Hybridization between different species followed by chromosome doubling.
- Polyploidy causes reproductive isolation, as polyploid individuals cannot mate with non-polyploid individuals, leading to the formation of new species.
- This isolation and increased genetic variation can result in the development of a new species.
(c) Explain how a newly discovered plant species would be classified and named. [7]
- Identification: Key features like structure and reproductive methods are observed.
- Comparison: The plant is compared with known species to see if it’s new.
- Taxonomy: The plant is classified into the correct taxonomic hierarchy (kingdom, phylum, class, etc.).
- Binomial nomenclature: The plant is given a scientific name, consisting of a genus and species name.
- Publication: The species is described in a scientific journal following taxonomic guidelines.
- Type specimen: A specimen is stored in a herbarium for reference.
- Ongoing review: The classification is reviewed as more research is done on the species.