Species, population and gene pool definitions
Laura Armstrong
Teacher
Recall Questions
This topic requires prior knowledge of genetic diversity. You can test your knowledge on this below.
What is an allele?
A different version of the same gene that may produce variation in a trait.
What causes genetic variation in a population?
Mutations, independent assortment of chromosomes, crossing over during meiosis, and random fertilisation.
Why is genetic diversity important in populations?
It increases the chances of survival of a population under changing environmental conditions by providing a variety of alleles that may confer selective advantage.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains species, population and gene pool definitions or read the full notes below. Once you've gone through the whole note, try out the practice questions!
What is a Species?
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A species is a group of organisms with similar characteristics that can interbreed to produce fertile offspring.
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Members of the same species share a common gene pool.
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Species are reproductively isolated from other species, they cannot interbreed successfully.
Example
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Panthera leo (lions) can reproduce with each other and produce fertile lion cubs.
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However, lions and tigers can produce a liger, but it is infertile - so they are considered different species.
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What is a Population?
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A population is a group of individuals of the same species that live in the same habitat at the same time, and can interbreed.
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Populations are dynamic — they can grow, shrink, or become extinct.
Example
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A herd of red deer living in a Scottish forest is one population of the species Cervus elaphus.
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A separate herd in another forest would be a different population of the same species. They are geographically isolated so are reproductively isolated as well.
No answer provided.
What is a Gene Pool?
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The gene pool is the complete range of alleles for all genes in a population.
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Greater genetic diversity = larger gene pool.
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Allele frequency (how common an allele is in the gene pool) can change due to:
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Natural selection
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Mutation
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Genetic drift in a small population
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Migration (gene flow)
Example
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In a population of rabbits, the alleles for fur colour may be black (B), white (b) or chocolate (bc).
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The gene pool includes all copies of B, b and bc alleles present in that population.
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Evolution is defined as a change in allele frequency in a gene pool over generations.
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A small gene pool can reduce genetic variation and increase risk of genetic disorders.
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Key Terms
- Species: Organisms capable of interbreeding to produce fertile offspring.
- Population: Group of individuals of the same species in the same habitat at the same time that can interbreed.
- Gene Pool: All alleles of all genes in a population.
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Exam Tip
Don’t confuse gene pool, genetic diversity, genotype and genome. Learn the exact definitions!
No answer provided.
(a) Define the term gene pool. (1 mark)
(b) State what is meant by a population. (2 marks)
(c) Define the term species. (2 marks)
(a) Gene pool – The complete range of alleles present in a population.
(b) Population – A group of organisms of the same species living in the same area at the same time and capable of interbreeding.
(c) Species – A group of organisms that can interbreed to produce fertile offspring.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!