UNIT 7: Genetics, populations, evolution and ecosystems

Define the term genotype.

The genotype is the genetic constitution of an organism.

Define the term phenotype

The phenotype is the expression of the genetic constitution (genotype) and its interaction with the environment.

What are alleles?

Alleles are different forms of a single gene.

True or false:
There is only one allele of a single gene.

False.
There may be many alleles of a single gene.

Complete the sentence.
Alleles may be _____ , _____ , or ______ .

Alleles may be dominant, recessive or codominant.

What is a dominant allele?

A dominant allele is one whose characteristic is expressed in the phenotype, even if there is only one copy.

What is a recessive allele?

A recessive allele is one whose characteristic is only expressed if two copies are present.

What are codominant alleles?

Codominant alleles are alleles which are both expressed in the phenotype.

Complete the sentence.
In a diploid organism, the alleles at a specific locus may be either be _____ or _____.

In a diploid organism, the alleles at a specific locus may be either homozygous or heterozygous.

An allele that codes for a characteristic is located on a sex chromosome.
What does this mean for the characteristic?

If an allele that codes for a characteristic is located on a sex chromosome, the characteristic is sex-linked.

A faulty recessive allele which causes colour blindness is located on the X chromosome.
Explain why males are more likely to have colour blindness than females.

Males are more likely to have colour blindness than females because males have one X chromosome, whereas females have two.
Males only need one allele, whereas females need to recessive alleles.

Define the term autosome.

The term autosome refers to non-sex chromosomes.

What is an autosomal gene?

An autosomal gene is a gene that is located on the autosomes.

Explain how autosomal linkage occurs.

Autosomal linkage occurs when genes are on the same autosome.
As the genes are close together, crossing over is less likely to occur.

If two genes are linked, how does this affect the offspring produced?

If two genes are linked, a higher proportion of the offspring will have their parents' genotype and phenotype.

When does epistasis occur?

Epistasis occurs when the allele of one gene affects the expression of the alleles of other genes.

What is the chi-squared (X²) test used for?

The chi-squared (X²) test is used to compare the goodness of fit of observed phenotypic ratios with expected ratios.

Compared to the critical value, what must the value of X² be to reject the null hypothesis?

The value of X² must be larger than the critical value to reject the null hypothesis.

Fill in the blank.
Species exist as one or more ___________.

Species exist as one or more populations.

Fill in the blanks.
A _________ as a group of organisms of the same ______ occupying a particular space at a particular time that can potentially __________.

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

Define the term gene pool.

The gene pool is the complete range of alleles present in a population.

Define the term allele frequency.

The allele frequency is the proportion of the total population with an allele.

What does the Hardy–Weinberg principle provide?

The Hardy–Weinberg principle provides a mathematical model, which predicts that allele frequencies will not change from generation to generation.

State the conditions under which the Hardy–Weinberg principle applies.

The Hardy–Weinberg principle applies under the conditions of a large population with no immigration, emigration, mutations or natural selection.
There must be random mating.

What can the Hardy–Weinberg equation be used to calculate?

The Hardy–Weinberg equation can be used to calculate the frequency of alleles, genotypes and phenotypes in a population.

Give the Hardy–Weinberg equation.

The Hardy–Weinberg equation is:
p² + 2pq + q² = 1
Where p is the frequency of one (usually the dominant) allele and q is the frequency of the other (usually recessive) allele of the gene.

p is the frequency of the dominant allele.
In the Hardy–Weinberg equation, what does p² represent?

In the Hardy–Weinberg equation, p² represents the frequency of the homozygous dominant genotype.

q is the frequency of the recessive allele.
In the Hardy–Weinberg equation, what does q² represent?

In the Hardy–Weinberg equation, q² represents the frequency of the homozygous recessive genotype.

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

In the Hardy–Weinberg equation, 2pq represents the frequency of the heterozygous genotype.

Fill in the blank.
Individuals within a population of a species may show a wide range of variation in _________.

Individuals within a population of a species may show a wide range of variation in phenotype.

What is variation in phenotype due to?

Variation in phenotype is due to genetic and environmental factors.

What is the primary source of genetic variation?

The primary source of genetic variation is mutation.

How is further genetic variation produced?

Meiosis and the random fertilisation of gametes during sexual reproduction produce further genetic variation.

Fill in the blanks.
________, _______ and ________ for the means of survival result in _______ survival and reproduction

Predation, disease and competition for the means of survival result in differential survival and reproduction.

What is another term for differential survival and reproduction?

Another term for differential survival and reproduction is natural selection.

Fill in the blanks.
Those organisms with phenotypes providing __________ _________ are likely to produce more offspring and pass on their favourable ______ to the next generation.

Those organisms with phenotypes providing selective advantages are likely to produce more offspring and pass on their favourable alleles to the next generation.

What is the effect of differential reproductive success on the allele frequencies within a gene pool?

Differential reproductive success will increase the frequencies of the favourable alleles within a gene pool.

Define the term disruptive selection.

Disruptive selection is where individuals with alleles for the extreme phenotype at both ends of the range are more likely to survive and reproduce.

What is evolution?

Evolution is the change in the allele frequencies in a population.

What is the result of reproductive separation of two populations?

Reproductive separation of two populations can result in the accumulation of differences in their gene pools.

How do new species arise from existing species?

New species arise when genetic differences between two populations in an existing species lead to an inability of members of the populations to interbreed and produce fertile offspring.

Describe the difference between allopatric and sympatric speciation.

In allopatric speciation, a physical barrier causes geographical isolation and hence reproductive isolation.
In sympatric speciation, reproductive isolation occurs without any physical separation.

Explain what happens to populations that are geographically separated.

Populations that are geographically separated will experience different conditions.
They experience different selection pressures, so different changes in allele frequencies occur.

When does genetic drift occur?

Genetic drift is the random cause of changes in allele frequency in small populations, due to chance.

Explain why genetic drift is important only in small populations.

Genetic drift is important only in small populations because it has a greater effect, as there are fewer alleles in small populations.
In larger populations, any random variations tend to even out across the whole population.

What is the result of evolutionary change over a long period of time?

Evolutionary change over a long period of time results in a great diversity of species.

What does a population consist of?

A population consists of all the organisms of one species in a habitat.

What do populations of different species form?

Populations of different species form a community.

Which two things form an ecosystem?

A community and the non-living components of its environment are the two things that form an ecosystem.

True or false: all ecosystems have the same size.

False. Ecosystems can range in size from very small to very large.

What does a species occupy within a habitat?

Within a habitat, a species occupies a unique niche governed by adaptation to both abiotic and biotic conditions.

Fill in the blank:
The certain size of a population of a species supported by an ecosystem is called the ________ ________.

The certain size of a population of a species supported by an ecosystem is called the carrying capacity.

Describe two ways the size of a population can vary.

The size of a population can vary as a result of the effect of abiotic factors and interactions between organisms.

Give five examples of abiotic factors.

Five examples of abiotic factors include the amount of light, water, or space available, the temperature of the surroundings or the chemical composition of the surroundings.

What are the three interactions between organisms?

The three interactions between organisms are interspecific competition, intraspecific competition, and predation.

Define interspecific competition.

Interspecific competition is competition between different species.

Define intraspecific competition.

Intraspecific competition is competition within a species.

Define predation.

Predation is when an organism eats another organism.

For slow-moving or non-motile organisms, what two methods are used to estimate the size of a population?

For slow-moving or non-motile organisms, randomly placed quadrats or quadrats along a belt transect are used to estimate the size of a population.

For motile organisms, what method is used to estimate the size of a population?

For motile organisms, the mark-release-recapture method is used to estimate the size of a population.

What are the assumptions made when using the mark-release-recapture method?

When using the mark-release-recapture method, the assumptions made include:
The marked sample has had enough time and opportunity to mix back in with the population.
The marking has not affected the organism’s chance of survival and the marking is still visible.
There are no changes in population size due to births, deaths, or migration.

A scientist wants to investigate the population size using mark-release-recapture.
Give the equation to calculate population size.

The equation to calculate population size is (number in first sample × number in second sample) divided by (number recaptured)

Fill in the blank: Ecosystems are _____ systems.

Ecosystems are dynamic systems.

What is succession?

Succession is the process where an ecosystem changes over time.

Where does primary succession occur?

Primary succession occurs on land that has been newly formed or exposed, where there is no soil or organic material.

What is a pioneer species?

A pioneer species is the first species to colonise an area.

Describe the process of colonisation by a pioneer species.

In the process of colonisation by a pioneer species, seeds and spores are blown in by the wind and begin to grow.

A volcano has erupted to form a new rock surface.
Explain why only the pioneer species can grow on the surface.

Only the pioneer species can grow because they are adapted to cope with the hostile abiotic conditions.

The pioneer species on the rock surface have died.
Explain the effect of this.

After the pioneer species die, microorganisms decompose the dead organic material (humus).
This forms a basic soil, changing the abiotic conditions so they are less hostile.

What two things can changes that organisms produce in their abiotic environment result in?

Changes that organisms produce in their abiotic environment can result in a less hostile environment and change biodiversity.

At each stage in succession, what can certain species do?

At each stage in succession, certain species can change the environment, so that it becomes more suitable for other species with different adaptations.

The conditions of the rock surface are less hostile.
Explain the effect of this.

After the conditions are made less hostile, new species with different adaptations can enter the land and grow.

Consider the new species that entered the land.
Suggest how the new species may change the environment.

The new species may change the environment so that it becomes less suitable for the previous species.

When does an ecosystem reach the climax community?

An ecosystem reaches the climax community when it is supporting the largest and most complex community of plants and animals.

True or false:
An ecosystem will no longer change when it reaches the climax community.

True.
An ecosystem will no longer change as it is in a steady state.

What does the conservation of habitats frequently involve?

The conservation of habitats frequently involves the management of succession.

Give two reasons why conservation is done.

Conservation is done to conserve species for biodiversity and conserve habitats.

Why is there a need to manage the conflict between human needs and conservation?

There is a need to manage the conflict between human needs and conservation in order to maintain the sustainability of natural resources.