AQA AS Biology

Topic Questions

4.3 Genetic Diversity: Mutations & Meiosis

1a2 marks

Table 1 shows three students’ examínation answers to a question that required a definition of the term, ‘mutation’. One student wrote a correct answer, whereas the other two did not. Choose the correct definition and explain why one other definition is not correct. 

Table 1

 Student

 Student’s definition of ‘mutation’

 Aamir

 “A change in a gene to adapt to changes in the environment”

 Beatrice

 “A random copying error in the DNA base sequence”

 Charlie

 “An adaptation that causes variation within a species”

1b1 mark

Place a tick (☑) in the correct box to identify the phase of the cell cycle when most mutations occur. 

  ⃞   Prophase

  ⃞   Metaphase

  ⃞   Interphase

  ⃞  Cytokinesis

1c2 marks

The DNA triplet TGA eventually codes for the amino acid threonine. A base substitution mutation alters that triplet to TGT, which also codes for threonine. Predict and explain the effect of this mutation on the phenotype of the organism it occurred in. 

1d1 mark

Name the property of the genetic code illustrated in part c).

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2a1 mark

Mutations can result from changes to small sections of DNA, but can also occur at the whole-chromosome level in a type of mutation known as a chromosome mutation. State how this type of mutation can occur.

2b2 marks

In addition to mutation, sexual reproduction can also introduce variation into a species. There are three processes that each introduce a degree of variation into a species during sexual reproduction. Two of these are:

  • Independent assortment (or segregation) of chromosomes in meiosis;
  • Random fertilisation (which sperm fertilises which egg).

Name and describe one other process that introduces variation during sexual reproduction.

2c2 marks

Table 1 gives some statements about meiosis in human cells. 

Table 1

Statement

Applies to meiosis / TRUE or FALSE

 2 daughter cells produced

FALSE

 Daughter cells show variation

 

 Daughter cells have the full   number of chromosomes

 

 Two cycles of division

 

 Produces gametes

 

Complete Table 1 with TRUE or FALSE / T or F in each empty box of the table. The first row has been completed for you. 

2d1 mark

The generation of genetic variation in meiosis allows different combinations of alleles to be formed within a species. Define the term allele

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3a2 marks

Explain the purpose of meiosis in living organisms;

3b1 mark

During the various phases of meiosis I and II, numbers like n and 2n are used. State what the number n denotes in such notation.

3c2 marks

Figure 1 below shows a simplified life cycle of a fern plant.

Figure 1

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Identify the types of cell division taking place at the positions marked A and B on Figure 1.

3d1 mark

Name the process taking place at the position marked C in Figure 1.

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4a2 marks

Figure 1 shows the fusion of gametes during fertilisation. 

Figure 1

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Name the two processes by which the eight gametes shown in Figure 1 (4 male, 4 female) have all come to possess a different range of alleles. 

4b1 mark

Identify the structure labelled 2n in Figure 1.

4c1 mark

Figure 2 shows a summary of the events of mitosis and meiosis. 

Figure 2

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Identify the event taking place at the stage marked X in Figure 2

4d2 marks

The stage marked Y on Figure 2 shows a change in the amount of genetic material in the cells. Describe the events that take place in order for this change to occur.

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5a2 marks

Flower buds from the species Arabidopsis thaliana, or thale cress, can be examined under the microscope to observe the visible stages of meiosis. Before staining and covering with a coverslip, the buds are treated in two stages:

  1. They are immersed in a cellulase solution. 
  2. They are macerated (crushed gently) on a microscope slide.

Suggest the purpose of each stage. 

5b1 mark

Suggest why flower buds were the tissue chosen for the experiment outlined in question 5a)

5c1 mark

During the experiment outlined in question 5a), some cells are observed with a new cell wall forming, creating two cells. Identify this phase of meiosis. 

5d2 marks

By observing the numbers of cells produced, explain how a scientist would know whether the first or second nuclear division is being observed in a particular cell or group of cells. 

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1a2 marks

Explain why it is important that one chromosome from each homologous pair ends up in each new cell during meiosis. 

1b2 marks

Meiosis is important in the life cycles of many organisms. One example of this is for organisms that reproduce sexually. Explain why it is important for these organisms. 

1c1 mark

A moss is a flowerless spore-producing plant. The spores are produced in capsules and  under favourable conditions can germinate into a branching green thread. Figure 1 shows some of the stages of the life cycle of a moss plant. Mark on the diagram with the letter X where meiosis occurs.

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1d5 marks

The processes in meiosis can lead to genetic variation among the haploid cells produced. Explain these processes and how they lead to genetic variation. 

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2a3 marks

Edwards syndrome is a rare but serious condition affecting chromosomes that influence birth weight and growth rate. As a result, it affects the chances of survival and most babies born with this syndrome will die shortly after birth. Figure 1 shows the chromosomes of an individual with Edwards syndrome. 

Figure 1

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Use Figure 1 to describe and explain the effects of Edwards syndrome of this set of chromosomes. 

2b3 marks

Edwards syndrome affects all of the chromosomes 18 in the body. Explain why. 

2c3 marks

Most babies born with Edwards syndrome will die before the age of one for various health complications. One of these complications is the abnormalities with the structure of the heart. Figure 2 below shows a heart abnormality that can exist in babies born with Edwards syndrome.
                                                                 

  Figure 2

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Use the diagram below to describe and explain why this abnormality may lead to early death.

2d2 marks

Describe how independent segregation results in genetic variation. 

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3a3 marks

Some of the processes in mitosis and meiosis are similar. Figure 1 shows a pair of chromosomes about to undergo cell division. 

 Figure 1

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State the name of X and explain its importance in cell division. 

3b3 marks

Describe the similarities and differences between homologous chromosomes.

3c3 marks

Figure 2 shows two cells after the completion of meiosis I. 

Figure 2

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Describe what happens in the next stages of meiosis.  

3d3 marks

Figure 3 shows three different cells in different stages of cell division. 

Figure 3

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Table 1

Process

Cell Q

Cell R

Cell S

Contains homologous chromosomes

     

Occurs in meiosis

     



Use Figure 3 to complete Table 1 by placing an X in the appropriate boxes. 

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4a2 marks

Figure 1 shows how the mass of DNA changes over time during two different types of cell division of a diploid organism. 

Figure 1 

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Explain what is happening at stage X and Y

4b1 mark

Identify which of the division types shown in Figure 1 represents meiosis and explain your answer. 

4c2 marks

Figure 2 shows a diploid cell containing different chromosomes. 

Figure 2

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Complete Figure 2 showing the appearance of the four different types of gametes produced by this diploid cell. 

4d4 marks

A diploid organism contains 38 chromosomes. Calculate the possible number of different combinations of chromosomes following meiosis and explain why this value may not be the actual number.   

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5a5 marks

DNA mutations can occur at any point during DNA replication but are usually removed by processes in the nucleus. Sometimes these mutations can go undetected. Describe what a base substitution is and explain its possible effects.

5b2 marks

Meiosis and mitosis share some similarities and differences within their cycles. Complete Table 1 below by inserting an X in the appropriate boxes. 

Table 1

Process

Mitosis

Meiosis

Involved in growth

   

Produces variation

   

Produces haploid cells

   

Occurs in plants

   

5c3 marks

Spider mites are small invertebrate organisms that are found on the island of Mauritius.It has very few chromosomes, 2n = 4. Figure 1 shows some cells that are undergoing cell division.

Figure 1 

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Which of these cells belong to the spider mite. Explain your answer. 

5d2 marks

A sample of cells was taken from the spider mites reproductive organs and the mass of DNA was determined. Some of the cells’ DNA had a mass of 3.4 arbitrary units (au) whilst for other cells, it was 6.8. Use your knowledge of the cell cycle to explain this observation. 

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1a1 mark

Marfan syndrome is an autosomal dominant genetic disorder that affects the connective tissue. This disorder is caused by mutations in the fibrillin 1 gene (FBN1), which is found on chromosome 15. There are 1300 different mutations that are known to alter the expression of this gene. Figure 1 shows the effects of two different mutations of the DNA on the base sequence of the mRNA. Table 1 shows the mRNA codons for four amino acids.

Figure 1

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Table 1

Amino acid

mRNA codon

Methionine

AUG

Cysteine

UGU

UGC

Tyrosine

UAU

UAC

Phenylalanine

UUU

UUC

 

Name the type of gene mutation represented by mutation 2.

1b1 mark

Use the information in Table 1 to identify amino acid P in Figure 1;

1c4 marks

Explain how mutation 1 and 2 in Figure 1 may affect the fibrillin protein for which this section of DNA is part of the code.

i)  Mutation 1 

ii) Mutation 2 

1d3 marks

Scientists have discovered that there are new mutations of the FBN1 gene and that mutagens in the environment may have contributed to these mutations. List three examples of mutagenic agents that may have caused these mutations.

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2a2 marks

Figure 1 shows a cell undergoing cell division.

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Explain how Figure 1 illustrates that the resulting daughter cells will be genetically
different. Give evidence from the diagram to support your answer.

2b1 mark

Figure 2 shows a pair of chromosomes during meiosis in a cell in the Drosophila
melanogaster (fruit fly) testis. The position of the alleles of some genes is indicated.

Figure 2

mq3b

Explain whether the chromosomes are homologous or non-homologous. 

2c4 marks

At the end of meiosis, each of the chromosomes shown in Figure 2 will be in a different haploid cell. Figure 3 represents the chromosomes inside the haploid cells.

Figure  3

mq3c

Determine the combinations of alleles that would be present on each chromosome. Illustrate your answer in Figure 3.

2d2 marks

Complete Table 1 using yes/no or numbers to compare mitosis and meiosis.

Table 1

Feature

Meiosis

Mitosis

 Number of nuclear divisions

   

 Number of daughter cells   produced

   

 Genetically different daughter   cells   produced

   

 Crossing over occurs

   

 Homologous chromosomes   pair up

   

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3a1 mark

Figure 1 shows the chromosomes found in a parent cell and the daughter cells produced after meiosis.

Figure 1

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Identify the daughter cell/s that contain a chromosome mutation by circling the cell/s in Figure 1.

3b3 marks

Explain how the spontaneous mutation (change in number of chromosomes) arose in the daughter cells (Figure 1) during meiosis.  

3c2 marks

Discuss the significance of meiosis in the life cycle of Pisum sativum (garden pea).

3d2 marks

Figure 2 shows a small part of the mRNA molecule for the CFTR protein.

Figure 2

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Table 1 shows the base triplets that code for three amino acids.

Table 1

Amino acid

mRNA codon

Histidine

CAC, CAU

Serine

UCU, UCC, UCA, UCG

Phenylalanine

UUU, UUC

Valine

GUA, GUG, GUU, GUC

Substitution of the ninth base (U) in the sequence shown in Figure 2 would not change the nature of the protein produced however if this base was deleted then the nature would change.  Explain why this is the case using the information provided. 


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4a2 marks

A Pisum sativum (garden pea) pollen mother cell is undergoing meiosis. During the initial phase of meiosis a pair of homologous chromosomes located in these cells can be represented by Figure 1. The two different letters represent two different genes.

Figure 1

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Define the term gene.

4b2 marks

At the end of meiosis the chromosomes were distributed to the four pollen grains as shown in Figure 2.

Figure 2

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Describe how the new allele combinations seen in Figure 2 were formed during meiosis.  

4c1 mark

Calculate how many different chromosomal combinations can result from meiosis in garden peas, which have a diploid number of 14. Assume no crossing over occurs.

4d2 marks

Derive a formula to calculate the number of combinations of chromosomes after the random fertilisation of a garden pea ovule and pollen nuclei.

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5a4 marks

Complete Table 1 with the appropriate key term for the definitions given.

Table 1

Key term

Definition

 

 The fixed position of a gene on a   particular DNA molecule 

 

 A change in the base sequence of a   chromosome

 

 The full range of proteins that a cell is   able to produce

 

 The base that is the complementary pair   of A/adenine in an mRNA molecule

5b2 marks

Figure 1 shows a cell undergoing cell division.

Figure 1

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Identify the type of cell division shown. Give evidence from Figure 1 to support your answer.

5c2 marks

Chlamydosaurus kingii (Australian Frillneck lizard) is a diurnal (active during the day) lizard whose distribution extends across northern Australia and into Papua New Guinea. If the lizard is startled it opens its mouth and flexes the muscles in its frill (a large fold of skin surrounding its throat) causing it to be raised. Scientists believe that the frill is used to deter predators and to attract females. Figure 2 shows the variation in the frill length of 164 male lizards from two different sites 150 km apart.

Figure 2

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Explain how meiosis may have caused the variation shown in Figure 2.

5d1 mark

Figure 3 shows the life cycle of Calvatia gigantea (giant puffball). In this life cycle, only the zygote and mature puffball are diploid. All the cells in all the other stages of the life cycle of the puffball are haploid, including the spores.

Figure 3

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Identify which letter in Figure 3 shows where meiosis occurs in the Giant puffball lifecycle.

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