Population genetics

In any one species, there is a large amount of genetic variation. The survival of a species is often linked with the extent of genetic variation within that species. This variation can be between individuals and between populations. Population genetics can tell a story of population change. Population genetics is also the unit of evolution.

Old Blue, the story of the black robin

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New Zealand’s black robin is an amazing story of how a species on the brink of extinction, with one breeding pair left, has now recovered to approximately 250 individuals. All of these individuals are descended from one female called Old Blue.

The gene pool of these individuals tells a story of the species population dynamics.

Photo of Old Blue courtesy Don Merton, Department of Conservation, and photo of plaque courtesy of Katie Labarbera

Rights: The University of Waikato Te Whare Wānanga o Waikato

Evolution by natural selection

Charles Darwin was a great observer. He voyaged around the globe observing the natural world. He noted that there was individual variation in populations, that offspring looked like their parents more than they looked like unrelated individuals of the same population and that, when there is overpopulation, there is competition.

He inferred from these observations that unequal reproductive success occurs – individuals with particular traits (and therefore genetics) are more likely to reproduce young that will themselves go on to reproduce and so on. He called this natural selection – or survival of the fittest (where fitness = reproductive success).

I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection.

Charles Darwin

The evolution of populations can be explained by considering the changes in the traits of organisms over time from a process of natural selection.

Gene pools

Allele frequencies in the gene pool of a population change by natural selection and mutation. When there is a small population, one-off chance events that impact a number of individuals can cause significant changes in allele frequencies. This is called genetic drift.

A population will experience a genetic bottleneck when numbers become so low and the few surviving individuals only carry a proportion of the variation from the original gene pool. New Zealand populations of takahē and the Chatham Islands black robin have experienced a genetic bottleneck.

New genetic research using palaeogenetic techniques has shed new light on another iconic species – the takahē. It has not only uncovered the significant impact of humans and past climate change on the takahē but has also led to new theories on their evolutionary history.

ZEALANDIA resources for teachers and students

Urban ecosanctuary ZEALANDIA has produced a comprehensive set of teaching resources designed to support Biology Achievement Standard 91158. The interactive Planning pathways using takahē resources has links to the student task information and aquestion bank, and the article Takahē – a context for learning has ideas and links to other useful resources. Many of the materials can be used as stand-alone resources for learning about takahē biology, evolutionary history, ecological niche, threats and conservation.