What is a polygenic trait?

A trait caused by the effect of multiple alleles from different genes.

What is an example of a polygenic trait?

Eye colour, body size, skin colour, type-2 diabetes, weight, hair colour...

What is pleiotropy?

When a single gene affects multiple traits (as opposed to a single gene affecting a single trait)

What is it called when the expression of one gene is controlled by other genes?

Epistasis

What makes a population susceptible to genetic drift?

A small number of individuals.

What is allopatric speciation?

The evolution of new species because of geographic isolation.

Give an example of allopatric speciation.

One species is separated into two populations because of rising sea levels. They don't interact for a very long time. Sea levels lower again and the two populations can no longer interbreed.

What is sympatric speciation?

When new species arise despite a lack of geographical isolation.

What is a gene?

A gene is a region of DNA that codes for specific proteins.

What are alleles?

Different forms of a particular gene.

What is the difference between an allele and a gene? Which is composed of the other?

An allele is a location on a chromosome that codes for the expression of a specific trait. It encompasses the genes that influence the proteins that express that trait.

An individual with two different alleles of a particular gene is said to be __________________ for that gene while an individual with two identical alleles is said to be ________________.

heterozygous, homozygous

Which pair of alleles is homozygous and which is heterozygous?

1. Aa

2.bb

1. heterozygous

2. homozygous

When both alleles contribute to the phenotype, the alleles are said to be what?

Codominant

If one allele masks the expression of the other the expressed allele is said to be ______________ while the masked allele is said to be _____________.

dominant, recessive

What are mutations?

Random changes in DNA the sequence of nucleotides of DNA. They can compromise a gene or control its expression.

How might mutations increase genetic variation?

They may create different phenotypes within a population, increasing the amount of alleles they have.

The reshuffling of genes that can occur during meiosis is called what?

Genetic recombination

How might genetic recombination increase genetic variation?

Despite no new genes being created there is the potential for new combinations of alleles to produce new phenotypes.

What is sexual reproduction?

When 2 parent organisms combine sex cells to produce offspring that are genetically distinct.

How might sexual reproduction increase genetic variation?

By combining random portions of either parents' DNA each offspring is genetically distinct from each other with combinations of traits that could be beneficial or not.

What is genetic drift?

A random process that occurs when genetic variation is lost because of random variation in mating, mortality, fecundity, and inheritance.

What is the bottleneck effect?

A reduction in genetic variation because of a severe reduction in population size

What is the founder effect?

When a small fraction of a bigger population colonize a new area but only bring a fraction of their original genetic diversity.

What are the three types of selection? What traits do they favour and punish?

Stabilizing selection: Favour intermediate, punish extremes

Disruptive selection: Favour extremes, punish intermediates

Directional selection: Favours one extreme only, punishes the other extreme and the intermediate

Scenario: A graph shows the fitness of snails compared to how thick their shells are. The graph shows that thicker shelled snails have a higher fitness. What type of selection are the snails undergoing?

Directional selection

Of the 3 types of selection only _________________ selection changes the mean frequency of a trait.

Directional