Genetics, populations, evolution and ecosystems

Define genotype.

All of the alleles that an organism carries on its chromosomes.

Define phenotype.

The observable characteristics of an organism, resulting from the interaction of its genotype and environmental factors.

What is a dominant allele?

An allele that is expressed in the phenotype even if only one copy is present (heterozygous or homozygous dominant).

What is a recessive allele?

An allele that is only expressed in the phenotype if two copies are present (homozygous recessive).

Define codominant alleles.

Alleles that are both expressed equally in the phenotype, resulting in a blend or the expression of both characteristics.

What does the term 'pure breeding' mean?

An organism that is homozygous for a particular trait.

Define a gene locus.

The specific fixed position of a gene on a chromosome.

What is monohybrid inheritance?

The inheritance of a single characteristic controlled by one gene.

What phenotypic ratio is expected from a cross between two heterozygous individuals in monohybrid inheritance?

A 3:1 ratio.

Define dihybrid inheritance.

The inheritance of two characteristics determined by two different genes located on two different chromosomes.

In human ABO blood groups, which alleles are codominant?

Allele IA and allele IB.

In human ABO blood groups, which allele is recessive to both IA and IB?

Allele IO.

What is sex linkage?

The expression of an allele that is dependent on the gender of the individual because the gene is located on a sex chromosome.

Why are males more likely to express X-linked recessive traits?

Because they have only one X chromosome and no equivalent locus on the Y chromosome, meaning they only carry a single allele for those genes.

What is a carrier in the context of sex-linked diseases?

A female who is heterozygous for a recessive sex-linked trait, meaning she does not express the disease but carries the allele.

Define autosomal linkage.

When two or more genes are located on the same autosomal chromosome.

How does autosomal linkage affect the number of possible allele combinations?

It reduces the number of possible combinations compared to genes on different chromosomes because the linked alleles are inherited together.

Define epistasis.

An interaction where one gene locus masks or suppresses the expression of another gene locus.

What is the phenotypic ratio for recessive epistasis?

9:3:4.

What is the phenotypic ratio for dominant epistasis?

12:3:1.

What is the purpose of the Chi-Squared test?

To determine if the difference between observed and expected results is small enough to have occurred purely by chance.

What is a null hypothesis in a statistical test?

A hypothesis stating that there is no statistically significant difference between the observed and expected results.

What is the minimum sample size required for a valid Chi-Squared test?

Over 20.

What are autosomal chromosomes?

Chromosomes that are not involved in sex determination (in humans, there are 22 pairs).

What is an allele?

An alternative form of a gene.

What is a null hypothesis in a scientific investigation?

A hypothesis stating that the results of an investigation will produce no statistical significance.

What are the three criteria for using a chi-square test?

The sample size must be over 20, data must fall into discrete categories, and only raw counts (not percentages or rates) can be used.

What is the critical value used for the chi-square test?

p = 0.05

How are degrees of freedom calculated for a chi-square test?

The number of categories minus one.

What happens to the null hypothesis if the obtained value is equal to or greater than the critical value?

The null hypothesis is accepted because the difference is not statistically significant.

What happens to the null hypothesis if the obtained value is less than the critical value?

The null hypothesis is rejected because the difference is statistically significant.

Define a population in biological terms.

A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed.

What is a gene pool?

The total number of alleles present in a population.

What does allelic frequency represent?

The proportion of a certain allele in a gene pool, expressed as a decimal or percentage.

What are the five assumptions of the Hardy-Weinberg principle?

No mutations, no migration, large population size, no selection (equal chance of passing alleles), and random mating.

What is the Hardy-Weinberg equation for allele frequencies?

p + q = 1.0

What is the Hardy-Weinberg equation for genotype frequencies?

p² + 2pq + q² = 1

In the Hardy-Weinberg equation, what does p² represent?

The frequency of homozygous dominant individuals (AA).

In the Hardy-Weinberg equation, what does 2pq represent?

The frequency of heterozygous individuals (Aa).

In the Hardy-Weinberg equation, what does q² represent?

The frequency of homozygous recessive individuals (aa).

What are three factors that contribute to genetic variation in a population?

Random fertilisation, meiosis (random assortment of alleles), and mutation.

How do environmental factors influence phenotypic traits?

Environmental factors can affect how genes are expressed, such as soil mineral content affecting flower pigment, often resulting in a normal distribution.

What is a biological niche?

The role of a species within its environment.

Why do organisms produce an unsustainably large number of offspring?

To increase competition (intraspecific competition) so that only those best suited to the environment survive to reproduce.

What is the primary driver of evolution via natural selection?

The differential survival and reproduction of individuals with advantageous alleles due to changing selection pressures.

Define directional selection.

Selection that occurs when environmental conditions change, favoring phenotypes at one extreme, causing the population mean to shift.

Give an example of directional selection.

The increase in antibiotic resistance in bacteria due to the presence of penicillin.

Define stabilising selection.

Selection that preserves the mean phenotype and reduces diversity when the environment remains stable.

Give an example of stabilising selection.

Human birth weight, where infants near the average weight have higher survival rates than those at the extremes.

Define disruptive selection.

Selection that favors both extremes of the phenotypic distribution over the mean.

What is speciation?

The process by which new species arise after a population becomes separated and cannot interbreed.

What is allopatric speciation?

Speciation caused by a physical barrier that separates a population, leading to reduced gene flow and different selection pressures.

What is sympatric speciation?

Speciation where new species evolve from a single ancestral species while inhabiting the same geographic region.

List three mechanisms that can cause sympatric speciation.

Chromosomal errors during cell division, mutations affecting courtship behavior, and anatomical changes preventing mating.

What is an ecosystem?

A community of organisms living in a particular area along with all the non-living (abiotic) elements of that environment.

Define the term 'niche' in an ecological context.

The particular role a species has in its habitat, consisting of its biotic and abiotic interactions.

What is carrying capacity?

The maximum size of a population of a species that an ecosystem can support.

What is intraspecific competition?

Competition for resources between members of the same species.

What is interspecific competition?

Competition for resources between members of different species, often occurring when they occupy the same niche.

Describe the predator-prey relationship cycle.

Prey population falls due to predation; predator population grows; prey population decreases further; predator population falls due to lack of food; prey population recovers.

What are two ways to measure the abundance of non-motile organisms?

Percentage cover and frequency.

What method is used to estimate the population size of fast-moving or hidden animals?

Mark-release-recapture.

List three assumptions of the mark-release-recapture method.

Marked individuals distribute evenly; there is no immigration or emigration; there are few or no births and deaths.

What is primary succession?

The process of colonization in an area previously devoid of life, such as a bare rock surface.

What are pioneer species?

The first organisms to colonize a harsh environment, such as lichens in primary succession.

What is a climax community?

The final, self-sustaining, and stable stage of succession.

How does secondary succession differ from primary succession?

Secondary succession occurs in an area where an existing community has been cleared, meaning a soil layer is already present.

What is the role of microorganisms in succession?

They decompose dead organisms, adding humus to the soil and making the environment more suitable for complex life.

What is conservation in the context of ecology?

The human management of Earth's resources, often involving the management of succession.

Why might humans use controlled burning in land management?

To stop the formation of a climax community and maintain a specific stage of succession.

How does temperature affect population growth?

Each species has an optimum temperature; survival decreases as the environment moves away from this optimum.

How does pH affect population distribution?

It impacts enzyme activity; organisms are more prevalent where the pH is optimal for their specific enzymes.

What is the effect of humidity on plant populations?

It affects transpiration rates, meaning only species adapted to specific humidity levels will survive.

Give an example of interspecific competition.

Red and grey squirrels in the UK competing for the same resources.

What is the purpose of a belt transect?

To estimate the population size or distribution of slow-moving or non-motile organisms across a habitat.