6 - Ecology and genetics

What is a genotype?

An individual's unique genome / collection of alleles.

What is a phenotype?

The visible characteristics of an individual as a result of their genotype interacting with the environment.

What is an allele?

A version of a gene (as a result of mutation).

What are the 3 causes of genetic variation in a population?

Mutation, meiosis, random fertilisation.

What are the 3 causes of genetic variation that occur during meiosis?

Crossing over / allele shuffling, independent assortment in meiosis I, independent assortment in meiosis II.

When does allele shuffling due to crossing over occur during meiosis?

Prophase I.

When does independent assortment of chromosomes occur during meiosis?

Metaphase I.

When does independent assortment of chromatids occur during meiosis?

Metaphase II.

What are the 4 chromosomal mutations that can occur during meiosis?

Deletion, inversion, translocation, duplication.

What are the 3 features of discontinuous genetic variation?

Qualitative differences in phenotype, no intermediate phenotypes, usually monogenic.

What are the 3 features of continuous genetic variation?

Quantitative difference in phenotypes, a range of phenotypes, polygenic.

What is a gene locus?

The position of a gene on a chromosome.

How many alleles are inherited for a single gene?

2.

How many dominant alleles are needed for its phenotype to be expressed?

1.

How many recessive alleles are needed for its phenotype to be expressed?

2.

What is meant if an individual is homozygous at a gene locus?

Alleles are identical.

What is meant if an individual is heterozygous at a gene locus?

Alleles are different.

What is meant by a true-breeding individual?

An individual homozygous for a particular trait.

What does it mean if a characteristic is monogenic?

It is controlled by one gene.

What is the expected phenotypic ratio for monogenic inheritance in offspring from heterozygous parents?

3:1.

What is a test cross?

A cross between an individual from the F2 generation and a true-breeding recessive individual in order to determine the F2 individual's genotype.

What is the expected outcome for a test cross if the F2 individual is homozygous?

100% dominant phenotype.

What is the expected outcome for a test cross if the F2 individual is heterozygous?

50% dominant, 50% recessive phenotype.

What is meant by codominance?

Both alleles contribute to the phenotype in a heterozygous individual.

What is meant if a gene has multiple alleles?

There are 3 or more possible alleles within the gene pool.

What is the human male combination for the sex chromosomes?

XY.

What is the human female combination for the sex chromosomes?

XX.

What is meant by the homogametic sex?

Sex chromosomes that are fully homologous and so result in only one type of gamete e.g. XX.

What is meant by the heterogametic sex?

Sex chromosomes that are not fully homologous and so result in 2 types of gamete e.g. XY.

What is a sex-linked characteristic?

Characteristic with a gene locus on a sex chromosome.

What is an X-linked characteristic?

Characteristic with a gene locus on the X chromosome.

How many alleles do males have for an X-linked characteristic?

1.

How many alleles do females have for an X-linked characteristic?

2.

Haemophilia is an example of which type of inheritance?

Sex Linkage.

Calculate the probability of the offspring being a female carrier if the father was a haemophiliac male and the mother carried no alleles for haemophilia.

50%.

What is dihybrid inheritance?

Inheritance involving 2 genes with loci on different chromosomes.

What is the expected phenotypic ratio for dihybrid inheritance in offspring from heterozygous parents?

9:3:3:1.

What are autosomes?

Chromosome (pairs) that are non-sex chromosomes.

What is autosomal linkage?

Multiple gene loci located on the same non-sex chromosome and inherited together.

What is a recombinant genotype?

A genotype only possible due to meiotic crossing over.

What is epistasis?

Where one gene masks or suppresses the expression of another gene.

What is antagonistic epistasis?

Where one gene suppresses the expression of another gene.

What is an epistatic gene?

Gene that prevents the expression of another gene.

What is a hypostatic gene?

A gene whose expression is prevented by another gene.

What is recessive epistasis?

Where the epistatic gene locus must be homozygous recessive in order to prevent the expression of the hypostatic gene.

What phenotypic ratio in offspring from heterozygous parents may suggest recessive epistasis?

9:3:4.

What is dominant epistasis?

Where the epistatic gene locus must have at least 1 dominant allele in order to prevent the expression of the hypostatic gene.

What 2 phenotypic ratios in offspring from heterozygous parents may suggest dominant epistasis?

13:3, 12:3:1.

What is complementary gene action?

Where 2 genes contribute to a final phenotype.

What is the Hardy-Weinberg principle?

In a stable population with no disturbing factors, the allelic frequencies will remain constant from one generation to the next, and there will be no evolution.

What are the 2 Hardy-Weinberg equations?

p + q = 1, p2 + 2pq + q2 = 1.

What are the 5 assumptions made if the Hardy-Weinberg principle applies to a population?

No mutation, random mating, no migration, large population size, no selection (natural or genetic drift).

What is genetic drift?

Changes in allele frequencies caused by chance events.

What are the 2 causes of genetic drift?

Genetic bottleneck, founder effect.

What is a genetic bottleneck?

When a population dramatically shrinks in size and then increases again.

What is the founder effect?

Establishment of a new, small population of a species derived from a larger, parent population.

Selection pressure can affect homozygous individuals. Why is a large gene pool necessary?

So the effect of chance variation in gene frequencies are minimized.

What is natural selection?

Changes in allele frequencies caused by environmental selection pressures favouring the survival of some individuals over others.

What is stabilising selection?

Natural selection that favours normal phenotypes due to unchanged environmental selection pressure.

What is directional selection?

Natural selection that favours one extreme phenotype due to a change in environmental selection pressure.

What is disruptive selection?

Natural selection that favours both extremes of a given phenotype due to a change in environmental selection pressures.

What is speciation?

Splitting of a population into 2 or more reproductively isolated populations.

What is meant by geographical isolation?

A population that is separated and reproductively isolated by geographical barriers such as rivers, lakes, mountains.

What type of speciation is a result of geographical isolation?

Allopatric.

What is reproductive isolation?

A population that is separated due to biological and behavioural changes.

What type of speciation results in reproductive isolation?

Sympatric.

What is sympatric speciation?

Speciation that occurs within populations in the same habitat.

What can lead to sympatric speciation?

Members of two different species interbreed and form fertile offspring.

Define the term 'abiotic factor'

Any non-living factor e.g. sunlight.

Define the term 'biotic factor'

Any living factor e.g. predators.

Give 3 examples of abiotic factors.

Temperature, light, pH, water, humidity, oxygen availability, edaphic(soil) factors.

Give 3 examples of biotic factors.

Competition, food, territory, breeding partners, predators.

Describe the importance of soil for plants.

Soil provides minerals for growth, water for photosynthesis, anchorage for roots.

Explain how particle size affects the air content and permeability of soils.

Small particles - few air spaces, retains water and floods easily e.g. clay. Large particles - lots of air spaces, does not retain water e.g. sand.

Define the term ecosystem.

Made up of all the living organisms that interact with one another in a defined area and also the physical factors present in that region e.g. rock pool.

Define the term producer.

Makes its own food, usually by photosynthesis to produce biomass (includes algae and plankton).

Define the term carnivore.

Eats only other animals.

Define the term herbivore.

Eats only plants.

Define the term omnivore.

Eats both plants and animals.

Define the term primary consumer.

Eats producers, usually a herbivore.

Define the term secondary consumer.

Eats primary consumers, usually an omnivore.

Define the term tertiary consumer.

Eats a secondary consumer.

Define the term trophic level.

Position or stage that something occupies in a food chain.

Define the term biomass.

The mass of living material present in a particular place or in particular organisms.

How do you find the dry mass of an organism?

Organism has to be killed and put in an oven to evaporate the water.

How do you calculate the net production of biomass made by a primary producer?

Net production = gross production – respiratory losses.

A group of scientists measured the gross production of a grassland area as 60gm-2yr-1. If respiration loss was 20gm-2yr-1, calculate the net production of this area of grassland.

40gm-2yr-1.

Why can't plants use all of the sunlight that hits them?

Some parts of a plant do not photosynthesize, some light passes through, some is the wrong wavelength.

Why isn't all energy transferred to the next trophic level?

Some parts of an organism are not digested, some parts are not eaten e.g. bones, some is used up for energy for movement/ respiration.

Approximately what % of energy is passed to the next trophic level?

10%.

What is the role of a herbicide?

Kills weeds that compete with crops - reduces competition.

What is the role of a fungicide?

Kills fungal infections that damage crops.

What is the role of an insecticide?

Kills insect pests that damage and eat crops.

What is the role of fertilizer?

A chemical that provides crops with the minerals required for growth.

Why is intensive farming beneficial?

Controls living conditions for organisms so that more energy is put into growing.

Define the term community.

All the populations of different species living and interacting with each other in a particular area.

What is meant by 'nitrogen fixation'?

When nitrogen gas is converted to nitrogen-containing compounds.

Give examples of two types of bacteria that are involved in nitrogen fixation.

Azotobacter and Rhizobium.

Explain why Rhizobium bacteria can be described as mutualistic.

They live in root nodules in peas and beans and they get carbohydrates from the plant; the plant gets amino acids from the bacteria.

What is meant by ammonification?

Production of ammonia from organic compounds e.g. urea, proteins and nucleic acids.