Populations
Biology: Cambridge International A Level, topic 17.2.5
Species and Populations
A population is defined as all the individuals of a species living within a specific area. Individuals in the same species can interbreed.
Species
- A species is a group of individual organisms that interbreed and produce fertile, viable offspring.
- According to this definition, one species is distinguished from another when matings between individuals from each species do not produce fertile offspring.
One population
- When organisms of the same species occupy a particular space at a particular time, they form a population.
- Individuals in the population can potentially interbreed.
Multiple populations
- Multiple populations may live in the same specific area.
- E.g. a forest includes populations of flowering plants, pine trees, insects and microorganisms.
- There can also be multiple populations of the same species.
- E.g. there are populations of pine trees throughout the Northern hemisphere.
Gene Pool and Allele Frequency
Gene pool and allele frequency are key terms for understanding populations.
Gene pool
- The gene pool is the sum of all the alleles in a population.
- Every individual has a different combination of alleles in their chromosomes.
- Populations of species share a gene pool.
Allele frequency
- Allele frequency is the rate at which a specific allele appears within a population.
- If an allele is particularly advantageous for survival, an individual that possesses it will be more likely to reproduce than an individual that does not.
- This means the allele is more likely to passed onto its offspring.
- Over time, this allele will increase in frequency.
Test yourself on Populations
Which of the following statements about species in a population are true?
Which of the following statements about gene pool and allele frequency are true?
Which of the following is NOT a consequence of an advantageous allele?