The Hardy-Weinberg principle is used in the investigation of population genetics.

What does the Hardy-Weinberg principle predict about populations?

In a population of snails, the banding of shells is controlled by a single gene with two alleles.

The allele B, for unbanded shells is dominant to the allele b, for banded shells.

A population of snails contained 64% unbanded snails.

Use the Hardy-Weinberg equation to calculate the percentage of this snail population you would expect to be heterozygous for this gene.

Give two assumptions that are made when using the Hardy-Weinberg equation.

A scientist investigated the banding pattern in another population of snails.

He found that the frequency of the recessive allele was much lower.

A statistical test showed that the difference between the two frequencies of the b allele was significant at the p = 0.05 level.

Use the terms probability and chance to explain what this means.

The Hardy-Weinberg equation is used by scientists to investigate the gene pools of populations.

What is a gene pool?

In a population of cattle, coat colour is controlled by one gene with two codominant alleles.

C^R represents the allele for a red coat and C^W represents the allele for a white coat.

When red cattle are crossed with white cattle, they produce offspring with a roan coat (a mixture of red and white hairs).

In a population of 56 cattle, 7 cows had a white coat.

Use the Hardy-Weinberg equation to estimate how many cattle in this population had a roan coat.

The actual number of cattle in this population that had a roan coat was 28.

Use the information above to calculate the actual frequency of the C^R allele.

Do not use the Hardy-Weinberg equation in your calculation.

What does the Hardy-Weinberg principle predict about the frequency of the C^R allele after another 5 generations?

There are around 150 species of lizards belonging to the same genus in the Caribbean islands.

Scientists believe that these species evolved from a single population in mainland USA.

What is meant by the term population?

Individual lizards within a population show phenotypic variation.

Give the two types of factor that cause this variation.

Explain how the different species of lizards found in the Caribbean islands could have evolved from a single population.

Describe how biologists could confirm that the lizard populations found on different Caribbean islands are separate species.

Scientists believe that the striped fur of a tiger helps to provide camouflage within their habitat.

State the type of adaptation represented by striped fur.

Explain how a tiger with striped fur might have evolved from a population of tigers without stripes.

Another gene determines whether tigers produce melanin pigment in their hair.

The allele T, for orange fur with black stripes is dominant to the allele t, for white fur with black stripes.

Captive breeding programmes aim to conserve the numbers of both orange and white tigers.

Suggest why the Hardy-Weinberg principle cannot be used to predict the frequencies of alleles controlling fur colour in the worldwide zoo population of tigers.

1 in 10,000 Bengal tigers have white fur with black stripes.

Use the Hardy-Weinberg equations to calculate the percentage of Bengal tigers that are heterozygous for this gene.

The apple maggot fly, Rhagoletis pomonella, is a species of fruit fly that lay their eggs on fruit.

Initially, apple maggot flies lay their eggs on hawthorn fruit, however a distinct form of maggot fly emerged in the 19th century that lay eggs on apples only.

Scientists believe these two forms of fly may now be considered as separate species.

One way in which two species can emerge from a common ancestor is by allopatric speciation.

What is allopatric speciation?

Describe how the two forms of apple maggot fly arose by sympatric speciation.

Describe how scientists could investigate the level of molecular similarity between the two forms of apple maggot fly.

Many antibiotics work by binding to receptors on the plasma membranes of bacterial cells.

Gene mutations resulting in altered receptors can cause bacteria to develop resistance to specific antibiotics.

Mutation is one cause of genetic variation within eukaryotes and prokaryotes.

Give two other causes of genetic variation.

Explain how a gene mutation providing resistance to an antibiotic can become widespread within a bacterial population.

What type of natural selection takes place when a gene for antibiotic resistance spreads throughout a bacterial population?

Explain why.

Suggest why the increasing prevalence of antibiotic-resistant bacteria is a major concern to the human population.

A group of scientists investigated the variation in clutch size (the number of eggs laid in a nest) in the barn swallow, Hirundo rustica.

The diagram below shows their results.

The barn swallow shows discontinuous variation in colour.

Suggest one other phenotypic characteristic in which barn swallows may show a discontinuous pattern of variation.

Suggest one phenotypic characteristic in which barn swallows may show a continuous pattern of variation.

Describe the pattern shown by the variation of clutch size in barn swallows.

Explain the type of selection that is occurring in the diagram above.

Feather colour in a species of bird is controlled by a pair of codominant alleles.

The allele C^B codes for black feathers and the allele C^W codes for white feathers.

Birds with both alleles are blue-feathered.

In a population, 16% of chickens had black feathers.

Use the Hardy-Weinberg equation to calculate the frequency of the C^W allele in this population.

The cheetah, Acinonyx jubatus, shows less intraspecific variation than other large cats.

What is intraspecific variation?

Some scientists believe that the modern cheetah population has low genetic diversity due to the population undergoing a recent genetic bottleneck.

Explain how a genetic bottleneck would lead to low genetic diversity.

Ecologists fear that genetic drift may affect the remaining cheetah populations.

Explain why genetic drift is a concern for small cheetah populations.

Cheetahs can run up to 60 miles per hour to catch their prey.

Their ancestors could only run up to 20 miles per hour.

Explain how natural selection has led to the increase in the speed of the cheetah.

Some scientists believe that cheetahs share a common ancestor with pumas.

A cause of this speciation could be that their ancestors were reproductively isolated.

State three other conditions that must be present in order for speciation to occur.

The process of selective breeding has been used over the years to increase the milk production of dairy cows.

Modern cows have larger udders compared to wild cattle from which they have been produced.

Describe how modern cows have been produced from less productive wild cattle ancestors.

Farmers use other ways to improve productivity of their animals.

Suggest one other way modern farmers may improve productivity of their animals.

Selective breeding is also used for other animals such as cats.

Some cats are selectively bred so that they do not provoke an allergic response in humans.

Suggest two other reasons why breeders might selectively breed cats.

Selective breeding can cause problems of inbreeding.

Suggest one problem that inbreeding causes.

Farmers use selective breeding to improve disease resistance in their crops.

What is another term for selective breeding?

Describe how selective breeding can result in disease-resistant crops.

Farmers should also preserve the wild populations of crop.

Give two reasons why it is important to maintain viable wild populations of crop plant species.

Farmers also use selective breeding to improve the milk yield of dairy cattle.

Give three reasons why why improving milk yields in cattle by selective breeding may be more difficult than improving crop yields by selective breeding.

Other than disease resistance, give two examples of crop features that farmers may improve using selective breeding.

The long-tailed widowbird, Euplectes progne, is a species of bird found in areas of open grasslands, marshes, and tall grasses.

During the non-breeding season, both male and female long-tailed widowbirds look the same.

However, from October to April, breeding males develop an exceptionally long tail (up to 50 cm).

The diagram below shows a male long-tailed widowbird during breeding season. 

Suggest one reason for male long-tailed widowbirds to develop a long tail during mating season. 

A group of scientists measured the tail length of male long-tailed widowbirds over a period of years.

Their results are shown in the diagram below.

Name the type of selection shown in this graph, and explain why this selection affected the frequency of alleles in the population of long-tailed widowbirds. 

Another group of scientists investigated the genetic diversity within a population of long-tailed widowbirds. 

Explain what is meant by the term genetic diversity. 

Describe and explain how selection will affect genetic diversity of long-tailed widowbirds. 

A population of oysters has shell colours which vary along a continuum from light to dark.

Light oysters camouflage against the sand of the intertidal zone whereas dark oysters camouflage in the shadows of the rocks.

Suggest and explain why the numbers of oysters with shell colours in the intermediate range decreased over a period of 10 years.

What type of selection is occurring in this oyster population?

Explain your answer.

Describe a simple experiment that could be carried out to investigate whether light and dark oysters still belong to the same species.

A scientist wanted to investigate whether there was a significant difference between the numbers of light and dark oysters within this population.

Which statistical test should he use?

Give a null hypothesis for this investigation. 

The black-capped chickadee is a small, non-migratory songbird that lives in deciduous and mixed forests.

A group of biologists studied the nests of a population of black-capped chickadees.

For each nest, they recorded the number of eggs and the number of young that survived from the nest.

Their results are shown below. 

What type of selection is shown in the graph above? 

Describe the evidence for your answer to the question above. 

Explain why black-capped chickadees that lay fewer than 3 eggs or more than 11 eggs per nest are at a selective disadvantage. 

Other than genetics, name one other factor that may influence the number of eggs laid by a black-capped chickadee.

The cheetah, Acinonyx jubatus, is a member of the cat family, Felidae.

Cheetahs have a lightweight skeleton, an aerodynamic body frame and long leg and foot bones. 

Explain how a lightweight skeleton allows cheetahs to survive. 

Cheetah populations show less intraspecific genetic diversity compared to other members of the Felidae family.

Some scientists believe that a recent genetic bottleneck has caused this lack of diversity.

Other than a genetic bottleneck, suggest two reasons why cheetah populations might show low levels of genetic diversity. 

Apart from genetic factors, what other type of factor causes variation within a species?