Implications of Allele Variations Within a Population (College Board AP® Biology)

Genetic Variety and Fitness

• The level of genetic diversity within a species or population affects its ability to withstand environmental pressures

• A species that has very little genetic diversity but is perfectly well adapted to its niche will be able to reproduce very successfully

  • All the time that environmental conditions (biotic and abiotic factors) remain stable, the organism will thrive

  • There is plentiful food, very little competition, a stable climate etc., so the organism enjoys the benefits of natural selection

• However, as soon as the environment changes for any reason, its lack of genetic diversity exposes the species to decline or even extinction

• The species's low allele variety within the species renders the species susceptible to being wiped out quickly

• Had the species a wider genetic diversity in the first place, there would be more chance of natural selection allowing certain individuals, carrying advantageous alleles, to endure

  • The species would be more resilient to environmental change

Examples of Genetic Variety Affecting Species Fitness

1. California condors

CC BY-SA 2.0 Don Graham, via Wikimedia Commons

• The California condor (Gymnogyps californianus) is a the largest North American land bird

• The species went into decline in the 20th century due to human activity; use of DDT in agriculture, poaching, lead poisoning all contributed to its decline

• Low population numbers in the first place contributed to the low genetic diversity within the species, with consequent low resilience to environmental factors

• Only a captive breeding program, led by San Diego Wildlife Park and Los Angeles Zoo, has allowed numbers in the wild to increase, although the species remains endangered

2. Black-footed ferrets

USFWS Mountain-Prairie, Public domain, via Wikimedia Commons

• The black-footed ferret (Mustela nigripes), also known as the American polecat, is critically endangered

• Its diet mainly consists of prairie dogs (Cynomys socialis), a rodent

• Prairie dogs have been identified as agricultural pests and have been exterminated from farms in certain areas across the USA and Canada

• Habitat loss of the prairie dog has meant that their main predator, the black-footed ferret, has suffered a reduction in the availability of its main food source

• Black-footed ferrets are not resilient to environmental perturbations because they have a low species diversity of alleles

3. Prairie chickens

CC BY 2.0 Ron Knight, via Wikimedia Commons

• The prairie chicken or pinnated grouse (Tympanuchus cupido) is sometimes called a boomer, thanks to its distinctive mating call

• It has become highly endangered in its native North America due mainly to habitat loss

• Their niche is undisturbed tallgrass prairie land, which has been lost in large mounts to agricultural uses in the 20th and 21st centuries

• Again, human led conservation programs have allowed the prairie chicken to endure in small pockets of managed prairie land

4. Potato blight

I.Sáček, CC0, via Wikimedia Commons

• Potato blight is a protoctist borne disease of potato crops, caused by the species Phytophthora infestans

  • The pathogen is unusual as it has some fungal characteristics

  • It is transmitted via spores

  • The first signs of potato blight are small, dark brown marks on the leaves which quickly increase in size and number

  • The protist destroys potato (and tomato) crops leaving them completely inedible

• This disease caused the infamous potato famine in Ireland in the mid 19th century, killing around 1 million people and contributing largely to the emigration of Irish people to other countries, notably to north America

• Agriculturalists use this example as a case study on the importance of maintaining genetic diversity within the population of food crop plants