Genetic Diversity: Mutations & Meiosis (AQA A Level Biology)

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

Table 1

Name the type of gene mutation represented by mutation 2.

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

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 

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.

Figure 1 shows a cell undergoing cell division.

Figure 1

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

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

Explain whether the chromosomes are homologous or non-homologous. 

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

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

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

Table 1

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

Figure 1

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

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

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

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

Figure 2

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

Table 1

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. 

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

Define the term gene.

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

Figure 2

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

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.

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

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

Table 1

Figure 1 shows a cell undergoing cell division.

Figure 1

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

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

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

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

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

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

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. 

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.

Figure 1

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

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

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

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

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

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

Describe how independent segregation results in genetic variation. 

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

 Figure 1

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

Describe the similarities and differences between homologous chromosomes.

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

Figure 2

Describe what happens in the next stages of meiosis.  

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

Figure 3

Table 1

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

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

Figure 1 

Explain what is happening at stage X and Y. 

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

Figure 2 shows a diploid cell containing different chromosomes. 

Figure 2

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

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.   

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.

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

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 

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

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.