Genetic Variation in the Founder’s Effect, and the Bottle Neck Effect.

Genetic Variation in the Founder’s Effect, and the Bottle Neck Effect

Genetic Variation

How can genetic diversity be increased?

How can genetic diversity be decreased?

List as many ways as you can think of

Learning Objectives

• Understand what is meant by the ‘Founder effect’ and how it results in a loss of genetic diversity

• Explain how genetic diversity is effected as a result of population bottlenecks

• Look at selective breeding as an artificial bottlenecking

Key terms

Genetic diversity

Allele frequency

Genetic Drift

Key terms

Genetic diversity – genetic differences between individuals within a population (in terms of alleles)

Allele frequency – how often a particular allele occurs within a population.

Genetic Drift – also known as allelic drift, is the change in the frequency of a gene variant (allele) in a population due to random sampling of organisms.

The Founder effect

The Mainland

Island

The Founder effect

The Mainland

Island

Population

The Founder effect

The Mainland

A few individuals colonise a new isolated area

There may be a higher frequency of one allele in the founder population just by chance

This allele needn’t have been very common in the original population

The island population grows

Island

…after a few generations

Island

The green allele may be lost completely if individuals fail to leave offspring carrying it

…after a few generations

Island

The green allele may be lost completely if individuals fail to leave offspring carrying it

…after a few generations

Island

Mutations may occur creating new alleles

…after a few generations

Island

The new allele becomes more common

The 2 populations now look very different!

The Mainland

Island

The Founder Effect• Occasionally a small group of individuals may migrate away or

become isolated from a population

• The ‘founding’ population is only made up of a small number of individuals. Inbreeding may be a problem if individuals are closely related

• It may have a non-representing sample of alleles from the parent population

• The colonizing population may evolve quite differently from the original population, especially if the environment is different

• Certain alleles may go missing all together as a consequence, resulting in a loss of genetic diversity

Some examples of the founder effect in action…

The Fugates of Kentucky

The Amish people, Pennsylvania

The Amish People

• 200 in founding population

• Within community marriages

• Recessive conditions are common• Haemophilia• Dwarfism (1/14 carry the gene)• Still births/infant deaths• Physical deformaties

‘The Royal Disease’

• Haemophilia

The Tsars

The Fugates• Small founding

population• Mountain communities• 2 of the founders were

carriers of a recessive allele

• Blue skin!

Population Bottlenecks

• Ecological events may reduce population sizes dramatically e.g. earthquakes, floods, fires.

• Disasters that are unselective .• Small surviving populations are unlikely to be

representative of the original population.• By chance alleles may be overrepresented

among survivors, some may be eliminated completely.

Samples of the Bottle Neck Effect in Action

Northern Elephant Seals:• Hunted close to extinction• Individuals on islands survived• Reduced genetic diversity compared with

southern elephant seals

Cheetahs

• 10,000 years ago all but 1 species had died out• Severely threatened• Very low genetic diversity resulting in poor sperm

quality among males• Females forced to breed with close relatives

• Inbreeding generally decreases the fitness of a population (an inbreeding depression)

https://www.youtube.com/watch?v=Q6JEA2olNts

Skittles bottleneck gameDifferent coloured skittles represent different alleles.1. Count the number of individuals in the population in your bottle, calculate the

frequency of each colour allele (%).2. Mix your sample of alleles in the bottle.3. Let 5 alleles through the bottleneck after a disaster causing a crash in population

numbers.4. Create a table and Record the colours & numbers of these 5 alleles.5. When each individual in this generation dies it can leave a maximum of 2 offspring

(or 2 skittles of the same colour) unless you do not have enough of this particular colour, in which case the individual has failed to reproduce. Record the new allele frequencies.

6. Remove the original population from the bottle and put in the survivors.7. Repeat the process of letting 5 individuals through a bottleneck, recording the allele

frequencies, letting them reproduce if possible and recording the allele frequencies again.

Repeat instructions 3-7 for 5 disasters

How to Calculate Allele Frequency*Remember*: Allele frequency is how often a particular allele occurs within a population.

• To determine the allelic frequencies we simply count the number alleles of phenotype we are examining and divide this number by the total number of alleles from the population.

Example: Total number of memebers in Population 23 Total # of Red 5 Frequency of Red = 5/23 = 22%Total # of Purple 4 Frequency of Purple = 4/23 = 17%Total # of Yellow 2 Frequency of Yellow = 2/23 = 1%

Similarities and differences between the Founder Effect & Bottlenecking

HOMEWORK

Similarities and differences between the founder effect & bottlenecking

Similarities DifferencesBoth are followed by genetic drift which results in changes in allele frequencies

In Bottlenecks individuals are killed, reducing the choice of mates, in the founder effect individuals are ecologically separated

Initially genetic diversity is lost in both systemsBoth involve a small number of individuals breeding with each other, both may involve inbreeding among close relativesBoth may result in a new population which carries alleles that are unlikely to be a true representation of the original group

Artificial SelectionArtificial selection is the intentional breeding of plants or animals. It means the same thing as selective breeding. Selective breeding is a technique used when breeding domesticated animals, such as dogs, pigeons or cattle. Some of these animals will have traits that a breeder will want to preserve.

*Farmers have cultivated numerous popular crops from the wild mustard, by artificially selecting for certain attributes. These common vegetables were cultivated from forms of wild mustard. This is evolution through artificial selection*

Genetic Engineering (Gene Manipulation)

• Genetic engineering, also called genetic modification, is the direct manipulation of an organism's genome using biotechnology.

• New DNA may be inserted in the host genome by first isolating and copying the genetic material of interest using molecular cloning methods to generate a DNA sequence, or by synthesizing the DNA, and then inserting this construct into the host organism. Genes may be removed, or "knocked out“ using these techniques.

• An organism that is generated through genetic engineering is considered to be a genetically modified organism (GMO).

• The first GMOs were bacteria in 1973. Insulin-producing bacteria were commercialized in 1982 and genetically modified food has been sold since 1994.

Glofish, the first GMO designed as a pet, was first sold in the United States December in 2003.