Genetic variants and mutation

The sequence of bases on one strand of a section of DNA is

TAC CGT AAT TAT

Which of these is the complementary sequence of DNA on the other strand of the double helix?

Which of these is the correct summary of the processes occurring during protein synthesis?

The table shows different mRNA codons for some amino acids.

UUU-AUG-UGU is one combination of codons that codes for the sequence of amino acids W–X–Y.

Give the number of other combinations that code for the same amino acid sequence.

Explain why most genetic mutations have no effect on the phenotype of an organism.

Use the information in the table and your own knowledge in your answer.

State one way that the incidence of mutations can be increased.

Cells use genetic information when carrying out protein synthesis.

Give the difference between a gene and a genome.

Describe the process of transcription.

Explain why a change in the sequence of bases in the DNA does not always result in a change in enzyme function.

Some characteristics are determined only by the genes, and some are determined by a combination of the genes and the environment.

Give an example of each type of characteristic in humans.

determined only by the genes

determined by the genes and the environment

Mutation can cause changes in the enzymes produced during protein synthesis.

State what is meant by the term mutation.

Explain the different effects that a single base mutation can have on transcription and translation and the production and activity of an enzyme.

Scientists investigate the rate of spontaneous mutations in yeast. They record the number of mutations per cell during mitosis and during meiosis. They count the mutations in three different strains of yeast and repeat each count. The mutation rates are counted per division per cell.

Calculate the mean mutation rate for strain 5207 during meiosis.

mean rate =_........ × 10⁸ per division per cell

Suggest why the mutation is calculated per division per cell rather than just per cell.

Comment on the differences in rates of mutation for mitosis and meiosis in the different yeast strains.

The photograph shows a plant called a snapdragon.

(Source: © BRIAN GADSBY/SCIENCE PHOTO LIBRARY) Selective breeding has been used to produce snapdragons with brightly coloured flowers.

Describe how selective breeding can produce snapdragon plants with brightly coloured flowers.

Micropropagation is often used to make copies of a snapdragon plant. Describe the process of micropropagation.

Scientists investigate the effect of exposing snapdragon explants to increasing amounts of ionising radiation. This is the scientists’ method.

• take a snapdragon plant and use micropropagation to produce many explants

• expose groups of explants to different amounts of ionising radiation

• grow the explants into plants and record the number of differences in their phenotypes compared with the original plant

• take samples of each of the plants and measure the number of differences in DNA nucleotides of each plant compared with the original plant

Give the reason why micropropagation is used to produce the plants to be tested.

What term is given to all the DNA in an organism?

The graph shows the scientists’ results.

Number of changes Number of in DNA different

Discuss the effects that increasing the amount of ionising radiation has on the snapdragons.

The chromosomes in a human cell can be photographed and then arranged in pairs to show the karyotype.

White blood cells are often used to show the chromosomes in the karyotype.

The chromosomes in white blood cells are larger and easier to see when the white blood cells divide.

Diagram 1 shows a karyotype.

Explain why a red blood cell cannot be used to show a karyotype.

State the type of cell division that occurs in white blood cells.

The karyotype in diagram 1 is from a male.

State how this can be deduced from the diagram.

Diagram 2 shows a karyotype from a white blood cell of another person.

The karyotype is from a female, and the person has a condition called Turner syndrome.

This condition affects the development of the ovaries so they may not produce normal quantities of sex hormones.

Comment on the differences between the karyotypes shown in diagram 1 and diagram 2 and the effects Turner syndrome will have on the person.

Use information from the question and your own knowledge in your answer.

Suggest how the difference in the chromosomes of people with Turner syndrome may have been produced.

6 (a) The diagram shows one strand of DNA from a section of a gene. ATTCCGAGT What would be the complementary sequence of bases on the messenger RNA produced from this strand of DNA?

The diagram shows a stage during protein synthesis.

Which row gives the correct names for the stage of protein synthesis shown and the sequence of bases labelled X?

Explain how a mutation in a gene can affect the phenotype of an organism.

In an accident at a nuclear power station, radioactive material was released into the surrounding areas of land. Scientists investigated the impact of this on a species of butterfly.

Samples of adult butterflies were collected from an area near the power station two months after the release of the radioactive material. The percentages of butterflies with abnormalities were calculated. The butterflies were then mated in the laboratory and the percentage of offspring with abnormalities calculated. The experiment was repeated with butterflies collected from the same area, 10 months after the release of the radioactive material.

Describe how the scientists could have sampled the population of butterflies in the area.

The results of the investigation are shown in the table.

The scientists concluded that the increased level of radioactivity has led to an increased rate of mutation of DNA. Discuss the scientists’ conclusion referring to data from the table to support your answer.

The bacterium H. pylori causes stomach ulcers.

The diagram shows this bacterium.

Which of these is found in this bacterium?

The bacterium has evolved to release an enzyme called urease.

The action of the bacterium neutralises the acid in the stomach.

What is the pH changed to?

Use the theory of evolution by natural selection to explain how H. pylori bacteria could have evolved to produce urease.

Probiotics are live microorganisms that can have health benefits when consumed.

Scientists investigate the ability of probiotics and cranberry juice to reduce the growth of H. pylori.

The scientists give various treatments to a group of people who have H. pylori.

The treatments are given daily for three weeks.

The scientists measure the mean percentage reduction of H. pylori for each treatment.

The table shows the scientists’ results.

Give two conclusions from these results.

Cell division can be by meiosis or by mitosis.

Where are cells dividing by meiosis found in a human?

Which part of a flowering plant is usually used to demonstrate cells dividing by mitosis?

The table lists features comparing the processes of meiosis and mitosis in human cells.

Complete the table by giving the missing information.

Cell division can cause variation in offspring.

Describe other causes of variation in offspring.

Scientists investigating a drug treatment use rats that are homozygous for many genes.

Suggest the advantages of using rats that are homozygous for many genes.

Variation in a population can have different causes.

Which of these will not lead to an increase in genetic variation in a population of plants?

Explain how a change in the DNA of a microorganism can reduce its ability to digest a substance.

Explain why a change in DNA may not affect the phenotype of an organism.

The molecules RNA and DNA are both involved in inheritance and protein synthesis.

Give two differences between the structure of a DNA molecule and the structure of an RNA molecule.

This sequence shows the order of bases on a DNA strand.

CATCATCCTCATCTA

Give the sequence of bases in the mRNA that would be produced from this strand.

The sequence of bases in the mRNA is used to code for the amino acids in a protein.

Calculate the number of bases required to code for an amino acid chain of 1400 amino acids.

A mutation results in a change in the sequence of bases in a DNA strand.

Discuss what effect a change in the sequence of bases could have on the functioning of the enzyme produced.

Give one way that the incidence of mutation could be increased.