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#165 Summary of Genetic technology

shahid Mandokhail A2 , Genetic Technology

1 Gene technology involves altering the genes in an organism, which is then said to be genetically modifi ed.

2 The usual way of genetically modifying bacteria is to insert a plasmid containing the desired gene into them.

3 The steps involved in the production of bacteria capable of synthesising human insulin are:
identifying the human insulin gene;
isolating mRNA and making cDNA using reverse transcriptase;
cloning the DNA using DNA polymerase;
inserting the DNA into a plasmid vector using restriction enzymes and DNA ligase;
inserting the plasmid vector into the host bacterium;
identifying the genetically modifi ed bacteria;
cloning the bacteria; and harvesting the human insulin.

4 The main advantage of treating diabetics with human insulin produced by gene technology is that it is chemically identical to the insulin that they would have produced had they not been diabetic. It also avoids any ethical issues that may arise from the use of insulin derived from an animal.

5 A promoter must be inserted along with the gene, because bacteria will not express a gene unless a suitable promoter is present.

6 The bacteria that have taken up the gene can be identifi ed using resistance to antibiotics or the presence of a fluorescing protein as markers.

7 Gene technology can provide benefits in, for example, agriculture, medicine and industry, but has the associated risk of the escape of the gene concerned into organisms other than the intended host. The risk is seen to be particularly high for genetically modified crops that are released into the environment to grow.

8 The social implications of gene technology are the benefi cial or otherwise effects of the technology on human societies.

9 Ethics are sets of standards by which a particular group of people agree to regulate their behaviour, distinguishing an acceptable from an unacceptable activity. Each group must decide, first, whether research into gene technology is acceptable, and then whether or not it is acceptable to adopt the successful technologies.

10 Electrophoresis is a technique that can be used to separate lengths of DNA (or RNA or proteins) of different sizes by applying an electric current to them. Small fragments move faster and therefore further than large ones, and can be made visible using radioactive labels or fluorescent compounds. Electrophoresis is used in genetic profi ling (genetic fingerprinting) and in DNA sequencing.

11 Cystic fibrosis is a genetic disease caused by a recessive allele of the gene that codes for the production of a chloride transporter protein called CFTR. People with two copies of the recessive allele produces thick, sticky mucus in their lungs, pancreas and reproductive organs.

12 Several attempts have been made to insert normal alleles of the CFTR gene into people with cystic fibrosis, a process called gene therapy. So far, there has been only limited success, because it is difficult to get the alleles into the cells. Even when this is successful, it needs to be repeated at frequent intervals because the cells have a very short natural lifespan.

13 Genetic screening involves testing people to find out if they carry any faulty alleles for genes that can cause disease. Genetic counsellors may help people who find that they have a disease-causing allele, or that their unborn child has, to make a decision about how to act on this information.

1. End-of-chapter questions

1 Different enzymes are used in the various steps involved in the production of bacteria capable of synthesising a human protein. Which step is catalysed by a restriction enzyme?

A cloning DNA
B cutting open a plasmid vector
C producing cDNA from mRNA
D reforming the DNA double helix

2 What describes a promoter?

A a length of DNA that controls the expression of a gene B a piece of RNA that binds to DNA to switch off a gene C a polypeptide that binds to DNA to switch on a gene
D a triplet code of three DNA nucleotides that codes for 'stop'

3 Which statement correctly describes the electrophoresis of DNA fragments?

A Larger fragments of DNA move more rapidly to the anode than smaller fragments.
B Positivelycharged fragments of DNA move to the anode.
C Small negatively charged fragments of DNA move rapidly to the cathode.

D Smaller fragments of DNA move more rapidly than larger fragments.

4 The table shows enzymes that are used in gene technology. Copy and complete the table to show the role of each enzyme.

5 Rearrange the statements below to produce a flow diagram showing the steps involved in producing bacteria capable of synthesising a human protein such as human growth hormone (hGH).

1. Insert the plasmid into a host bacterium.
2. Isolate mRNA for hGH.
3. Insert the DNA into a plasmid and use ligase to seal the 'nicks' in the sugar-phosphate chains.
4. Use DNA polymerase to clone the DNA.
5. Clone the modified bacteria and harvest hGH.
6. Use reverse transcriptase to produce cDNA.

7. Use a restriction enzyme to cut a plasmid vector.

6 a Genetic fingerprinting reveals the differences in variable number tandem repeats (VNTRs) in the DNA of different individuals. Explain what is meant by a VNTR. [3]
b Examine the figure, which shows diagrammatic DNA profiles of a mother, her child and a possible father of the child. Decide, giving your reasons, whether the possible father is the actual father of the child. [3]

[Total: 6]

7 a Copy and complete the table to explain the roles of primers and dideoxynucleotides in DNA sequencing.

[3]

b Explain what is meant by:
i gene therapy [1]
ii genetic screening [1]
iii genetic counselling. [1]

c Explain why it is easier to devise a gene therapy for a condition caused by a recessive allele than for one caused by a dominant allele. [5]

[Total: 11]

8 a Draw a genetic diagram to show how two heterozygous parents may produce a child with cystic fibrosis. Use the symbols A/a in your diagram. [3]

b State the probability of one of the children of these parents suffering from cystic fibrosis. [1]

[Total: 4]

The figure shows the CFTR (cystic fibrosis transmembrane conductance regulator) protein in a cell surface membrane.

a i Describe the normal function of the CFTR protein. [2] ii Use the letter E to indicate the external face of the membrane. State how you identified this face. [1]

b Cystic fibrosis is caused by a recessive allele of the CFTR gene.

i Explain the meaning of the term recessive allele. [2]

ii Explain how cystic fibrosis affects the function of the lungs. [3]

c As cystic fibrosis is caused by a recessive allele of a single gene, it is a good candidate for gene therapy. Trials were undertaken in the 1990s, attempting to deliver the normal allele of the CFTR gene into cells of the respiratory tract, using viruses or liposomes as vectors. Explain how viruses deliver the allele into cells. [2]

d In some people with cystic fibrosis, the allele has a single-base mutation which produces a 'nonsense' (stop) codon within the gene.

i Expalin how this mutation would prevent normal CFTR protein being produced. [2]

ii A new type of drug, PTCI24, enables translation to continue through the nonsense codon. Trials in mice homozygous for a CFTR allele containing the nonsense codon have found that animals treated with PTC124 produce normal CFTR protein in their cells. The drug is taken orally and is readily taken up into cells allover the body.

Using your knowledge of the progress towards successful gene therapy for cystic fibrosis, suggest why PTC124 could be a simpler and more reliable treatment for the disease. [3]

[Total: 15]

[Cambridge International AS and A Level Biology 9700/04, Question 2, October/November 2008]

2. End-of-chapter answers

1 B
2 A
3 D

Exam-style questions

6 a VNTR: a short length of highly repetitive DNA;

number of repeats and hence lengths of repeats diff er markedly in diff erent individuals; inherited: half VNTRs from father, half from mother;

only identical twins have the same VNTRs; [max. 3]

b four bands in child’s profile match four of the bands in the mother’s;

the other four bands match four bands in the father’s profile;

the possible father is the actual father; [3]

[Total: 6]

b i gene therapy: treatment of a genetic disorder by altering the patient’s genotype; [1]

ii genetic screening: determination of a person’s genotype using karyotype analysis for chromosome mutations and probes for identifying particular alleles; [1]

iii genetic counselling: a service that seeks to explain the nature of genetic disorders and probability of their transmission; [1]

c when a genetic disorder is caused by a recessive allele, the ‘normal’ allele is dominant;

adding a dominant allele allows some correct product to be made; the individual effectively becomes heterozygous;

the recessive allele may code for defective product or no product;

production of some correct product may cure the disorder;

adding a recessive allele cannot block a faulty dominant allele; [max. 5]

[Total: 11]

8 a

correct gametes; correct genotypes; correct phenotypes; [3]

b 1 in 4/0.25/25%; [1]

[Total: 4]

9 a i chloride channel; chloride moves out of cell by active transport; [2]

ii upper face because of presence of carbohydrate chains; [1]

b i allele: variant form of a gene; recessive: only aff ects phenotype when dominant allele is not present; [2]

ii thick, sticky mucus produced; mucus accumulates; reduced gas exchange; more infections; [max. 3]

c normal dominant CFTR allele added to viral DNA;

virus inserts DNA into cell; [2]

d i translation stopped at ‘stop’ codon; protein chain not completed; [2]

ii comparisons include: drug easily taken up by cells, whereas therapy is poorly taken up;

drug taken orally, whereas therapy must be inhaled into lungs;

no vector needed for drug, whereas virus vector for therapy may cause side-eff ects; [3]

[Total: 15]

#154 Summary Biodiversity and conservation

shahid Mandokhail A2 , Biodiversity

1 All living organisms may be classified into one of the five kingdoms: prokaryotes, protoctists, fungi, plants and animals.

2 Biodiversity includes the range of habitats (environments) and species in an area, and the genetic diversity within a species.

3 There are moral and ethical reasons for maintaining biodiversity, and also more practical ones. For example, we may be able to use plants to provide medicines, and animals to provide alleles to use in animal breeding.

4 Species may become in danger of extinction through habitat loss, change to their environment (perhaps as a result of pollution) and overexploitation by humans.

5 Conservation of an endangered animal species may involve captive breeding programmes, in which viable populations are built up in zoos and wildlife parks. These programmes try to ensure that the gene pool is maintained and inbreeding is avoided. At the same time, attempts are made to provide a suitable habitat in the wild, so that captive-bred animals can eventually be re-released into the wild. Local people are involved, because this increases acceptance of the project and the chances of its success.

6 Botanic gardens and seed banks help to conserve threatened plant species by breeding them for reintroduction into an appropriate habitat. Seed banks provide suitable conditions to keep different types of seeds alive for as long as possible. Samples of the seeds are grown into adult plants every now and then, so that fresh seed can be collected.

7 Many countries have protected areas called national parks, which often cover large areas. These are set up to conserve rare and endangered species and to maintain their habitats. Often legislation is passed to ensure their protection. In such areas, agriculture is controlled and building, mining and other industries strictly regulated. Access is often limited but not forbidden, as one aim of most such parks is to educate people about the importance of conservation. 8 Other, smaller, conservation areas may be created to protect particular species and habitats.

1. End-of-chapter questions

Which organism is a fungus?

2 Which of the statements about Protoctista are correct?

1 a eukaryote that is not a fungus, plant or animal is a protoctist

2 an organism with cellulose cell walls and chloroplasts may be a protoctist

3 an organism existing as a group of similar cells may be a protoctist

4 a single-celled heterotrophic eukaryote is a protoctist

A 1,2,3 and 4 B 1, 2 and 4 only C 2 and 3 only D 3 and 4 only

3 A gene bank is a store of the genetic variation of a species. Which of the following are gene banks?

1 captive animals in a zoo

2 plants in a botanic garden

3 seeds in a seed bank

4 plant cells growing in tissue culture

5 frozen sperm, eggs or embryos

A 1, 2, 3, 4 and 5 B 1, 2 and 3 only C 2, 3 and 4 only D 3, 4 and 5 only

4 Copy and complete the table to show the features present in the five different classificatory Kingdoms of living organisms. Use a tick (V") to show the presence of a feature and a cross (x) to show its absence.

Add caption

5 Distinguish between orthodox and recalcitrant seeds.

6 a Explain what is meant by biodiversity. [2]

b Over half of the living species of plants and animals live in tropical rainforests. Suggest why this is so. [4]

c Some rainforest species, for example the squirrel monkey in Costa Rica, are endangered. Suggest four ways to conserve an animal species such as the squirrel monkey.[4]

d List four practical reasons why humans should try to maintain biodiversity. [4]

[Total: 14]

7 a In many cases, the reason for an organism becoming endangered is the loss of its habitat as a result of human activity. List four ways in which human activity causes habitat loss. [4]

b In 1973, the population of African elephants in Kenya was about 167000 animals, but by 1989 the population had dropped to about 16000 animals. In 2010 the population had risen to about 36000 animals. Suggest explanations for these changes. [6]

c Explain:

i how captive breeding of animals, such as the scimitar-horned oryx, can help conserve an endangered species; [3]

ii how genetic diversity can be maintained during a captive breeding programme. [3]

[Total: 16]

8 The American crocodile, Crocodylus acutus, was classified as an endangered species by the USA in 1975. It is found in estuarine regions of southern Florida.

The salinity of the water was thought to playa part in the distribution of the American crocodile. The figure shows the number of American crocodile nest sites in areas with water of varying salinity in southern Florida.

a Describe the results shown in the figure. [3]

b Much conservation work has been done in the Everglades National Park in Florida, which is a large wetland area. As a result, the number of nest sites increased from eight in 1975 to 31 in 2000. This led to a rise in the number of crocodiles.

i Calculate the percentage increase in nest sites between 1975 and 2000. Show your working.[2]

ii Suggest two reasons why the population of crocodiles in the Everglades National Park has increased.[2]

[Total: 7]

[Cambridge International AS and A Level Biology 9700/42, Question 1, Mayljune2010,]

2. End-of-chapter answers

1 D
2 A
3 A
4

5 orthodox seeds: can be dehydrated and frozen for long-term storage;

recalcitrant seeds: cannot be dehydrated and frozen;

Exam-style questions

6 a biodiversity:
range/variety, of, species/communities/ecosystems;
the genetic variation within a species;
the genetic variation between species; [max. 2]

b high rate of photosynthesis/rapid growth of plants; allows large number of plant species;
available throughout the year;
provides niches for large number of animal species; [4]

c maintain as a captive population in a zoo/captive breeding;
set up conservation area/protect habitat from clearance;
ban, hunting/capture;
educate public/introduce ecotourism; [4]

d as resource for, food/materials;
as source of alleles for breeding to improve agricultural species;
as potential medicines; for ecotourism/leisure;
to maintain, food webs/nutrient cycles; [max. 4]

[Total: 14]

7 a clearing land for agriculture;
clearing land for housing;
clearing land for industrial building;
clearing land for, road building/railways/pipelines/
other infrastructure;
mining;
logging;
pollution/global warming; [max. 4]

b fall from 167 000 to 16 000 due to a combination of factors including:
ivory hunting;
game hunting;
hunting for meat;

killing after damage to village crops;
habitat loss;
rise after 1989 due to ban on ivory trading;
rise only to 36 000 because other factors still apply: habitat loss;
poaching;
killing after damage to village crops; [max. 6]

c i bred in several places so not all at risk from same disease;
increased numbers of animals;
allows return of animals to wild; [3]

ii close relatives are not interbred; e.g. siblings/father with daughter;
in-vitro fertilisation used to breed from distantanimals;
refer to embryo donation and use of surrogates; [max. 3]

[Total: 16]

8 a more nests in less saline areas;
22 nests at 0–5 parts per thousand compared with 1 at 31–35 parts per thousand;
anomalous result for 16–20 parts per thousand; [3]

ii more fresh water/lower salinity;
sites protected;
ecotourism encouraged;
ban on hunting;
less pollution; [max. 2]

[Total: 7]

#143 Summary of Selection and Evolution

shahid Mandokhail A2 , Selection and Evolution

1 Genetic variation within a population is the raw material on which natural selection can act.

2 Meiosis, random mating and the random fusion of gametes produce genetic variation within populations of sexually reproducing organisms. Variation is also caused by the interaction of the environment with genetic factors, but such environmentally induced variation is not passed on to an organism’s off spring. The only source of new alleles is mutation.

3 All species of organisms have the reproductive potential to increase the sizes of their populations, but, in the long term, this rarely happens. This is because environmental factors come into play to limit population growth. Such factors decrease the rate of reproduction or increase the rate of mortality so that many individuals die before reaching reproductive age.

4 Within a population, certain alleles may increase the chance that an individual will survive long enough to be able to reproduce successfully. These alleles are therefore more likely to be passed on to the next generation than others. This is known as natural selection.

5 Normally, natural selection keeps allele frequencies as they are; this is stabilising selection. However, if environmental factors that exert selection pressures change, or if new alleles appear in a population, then natural selection may cause a change in the frequencies of alleles; this is directional selection.

6 Over many generations, directional selection may produce large changes in allele frequencies. This is how evolution occurs.

7 The evolution of antibiotic resistance in bacteria and the spread of industrial melanism in moths are examples of changes in allele frequencies. The role of malaria in the global distribution of sickle cell anaemia is an example of how two strong opposing selection pressures can counterbalance each other in maintaining two alleles within certain populations.

8 A species can be defi ned as a group of organisms with similar morphology, behaviour, physiology and biochemistry that are capable of interbreeding to produce fertile off spring. In practice, however, it is not always possible to determine whether or not organisms can interbreed.

9 New species arise by a process called speciation. In allopatric speciation, two populations become isolated from one another, perhaps by some geographical feature, and then evolve along different lines until they become so diff erent that they can no longer interbreed. In sympatric speciation, new species may arise through polyploidy.

10 Artificial selection involves the choice by humans of which organisms to allow to breed together, in order to bring about a desirable change in characteristics. Thus artificial selection, like natural selection, can aff ect allele frequencies in a population.

1. End-of-chapter questions

1 Which of the following gives rise to genetic variation in a population?

1 crossing over and independent assortment in meiosis

2 different environmental conditions

3 random mating and fertilisation

4 mutation

A 1,2,3 and 4 B 1, 2 and 3 only C 1, 3 and 4 only D 2, 3 and 4 only

2 A species of finch living on an isolated island shows variation in beak size. Birds with larger beaks can eat larger seeds.

After a period of drought on the island, large seeds were more plentiful than small seeds and the average size of the finches' beaks increased.

What explains this increase in size of beak?

A artificial selection acting against finches with small beaks

B directional selection acting against finches with small beaks

C increased rate of mutation resulting in finches with larger beaks

D stabilising selection acting against finches with the smallest and largest beaks

3 Which effect of natural selection is likely to lead to speciation?
A Differences between populations are increased.
B The range of genetic variation is reduced.
C The range of phenotypic variation is reduced.
D Favourable alleles are maintained in the population.

4 There are three genotypes of the gene for the β-globin polypeptide: HbAHbA, HbAHbs and HbsHbs.

Copy and complete the table to show which genotypes have a selective advantage or disadvantage in different regions of the world.

5 The wings of butterflies are covered with microscopic scales that give them their colour and also provide waterproofing.

The wings of some species have large transparent areas through which the colour of the vegetation on which the butterfly has settled can be seen. Because they lack scales, these areas have poor waterproofing. The butterflies are eaten by birds.

a Describe two selection pressures that are likely to control the size of the transparent areas of the wings of these butterflies.
b In what circumstances might there be selection for larger transparent areas in the wings?

6 Rearrange the order of the following statements to give a flow diagram showing the evolution of resistance to the antibiotic streptomycin by the bacterium Escherichia coli.

1. Most of the population of E. coli is resistant to streptomycin.
2. A mutation in a DNA triplet of a plasmid, changing TTT to TTG, gives an E. coli bacterium resistance to streptomycin.
3. The resistant bacterium divides and passes copies of the R plasmid to its offspring.
4. Sensitive bacteria die in the presence of streptomycin as a selective agent.
5. The frequency of the mutated gene in the population increases.
6. The resistant bacterium has a selective advantage and survives.

7 Copy and complete the table to compare artificial selection with natural selection.

8 Pale and dark peppered moths were collected and placed on pale and dark areas of bark on trees in a park in Liverpool, England. Some of the moths were predated by birds. The results of the investigation are shown in the table.

a 40 dark moths were placed on dark bark. Calculate the number of moths taken by birds. Show your working. [2]
b Suggest an explanation for the differences in the numbers of moths taken by birds. [4]

[Total: 6]

9 The snail Cepaea nemoralis may have a yellow, pink or brown shell. Each colour shell may have up to five dark bands, or have no bands. Both shell colour and number of bands are genetically controlled. The snails are eaten by birds such as thrushes, which hunt by sight.

The following observations were made:

• Most snails living on a uniform background, such as short grass, have no bands.
• Most snails living on a green background, such as grass, are yellow.
• Most snails living on a non-uniform background, such as rough vegetation, have bands.

a Suggest an explanation for these observations. [4]
b Predict the phenorype of snails living on a dark background of dead leaves.[2]
c Suggest what will happen, during the course of a year, to the frequencies of the different alleles controlling shell colour and banding in a snail population living in deciduous woodland. (Deciduous trees shed their leaves in autumn. The background for the snails will be made up of dead leaves in the autumn and winter, and green vegetation in the spring and summer.)[4]

[Total: 10]

10 The heliconid butterflies of South America have brightly coloured patterns on their wings. A hybrid between two species, Heliconius cydno and H melpomene, has wing patterns that are different from both parental species.

An investigation was carried out to see whether the hybrid was a new species.

Separate groups of four butterflies, each consisting of a male and female of one of the parental species and a male and female of the hybrid, were placed together and their choices of mates recorded. The results are shown in the table.

a With reference to the information in the table, explain whether or not the results of the investigation suggest that the hybrid butterfly is a separate species. [4]
b Suggest how the ybrid could be reproductively isolated from the two parent species of butterfly. [2]
c Briefly describe how allopatric speciation can occur.[4]

[Total: 10]

2. End-of-chapter answers

1 C
2 B
3 A

5 a predation by birds, tending to increase the size of the transparent areas of the wings as they increase camoufl age;
rainfall, because smaller transparent areas give an advantage;

b increased predation/drier conditions;

6 2, 4, 6, 3, 5, 1
1 mark for every 2 correct answers

Exam-style questions

8 a 40 × 40 ÷ 100 = 16; [2]

b pale moths are camouflaged on pale bark, and dark moths on dark bark;

predators/birds, hunt by sight;

fewer moths taken that match bark;

refer to figures: 20% v. 44% of pale moths/15% v. 40% of dark moths; [4]

[Total: 6]

9 a camouflage from bird predators hunting by sight;

yellow blends into grass but pink or brown are easily seen;

bands break up outline against rough vegetation;

yellow or pink without bands are easily seen; [4]

b brown/five bands; [2]

c selection favours alleles for brown shell and for bands in autumn and winter;

selection favours alleles for yellow shell and few or no bands in spring and summer;

gradual change in selection pressures as seasons change;

keeps all alleles in the population; [4]

[Total: 10]

10 a behaves as good species with no intermating in relation to H. melpomene;

15 matings between H. melpomene males and females and between hybrid males and females; behaves as less good species in relation to H. cydno;

no matings between H. cydno males and hybrid females;

but three matings between H. cydno females and hybrid males; [max. 4]

b select mates on basis of wing colours and patterns;

hybrid wing pattern sufficiently different from parent species to give good isolation from H. melpomene; [2]

c needs geographical separation;

selection pressure diff erent in the separated populations;

different alleles selected for;

in time the diff erences between the two populations are so great that they do not interbreed should they happen to meet; [4]

[Total: 10]

#136 Summary of Inherited change

shahid Mandokhail A2 , Inherited Change

1 Meiosis consists of two divisions. The first division, meiosis I, separates the homologous chromosomes, so that each cell now has only one of each pair. The second division, meiosis II, separates the chromatids of each chromosome. Meiotic division therefore produces four cells, each with one complete set of chromosomes.

2 Diploid organisms contain two copies of each gene in each of their cells. In sexual reproduction, gametes are formed containing one copy of each gene. Each off spring receives two copies of each gene, one from each of its parents.

3 The cells produced by meiosis are genetically different from each other and from their parent
cell. This results from independent assortment of the chromosomes as the bivalents line up on the
equator during metaphase I, and also from crossing over between the chromatids of homologous
chromosomes during prophase I.

4 Genetic variation also results from random fertilisation, as gametes containing diff erent varieties
of genes fuse together to form a zygote.

5 An organism’s genetic constitution is its genotype. The observable expression of its genes is its phenotype.

6 Different varieties of a gene are called alleles. Alleles may show dominance, codominance or recessiveness. An organism possessing two identical alleles of a gene is homozygous; an organism possessing two different alleles of a gene is heterozygous. If a gene has several diff erent alleles, such as the gene for human blood groups, these are known as multiple alleles.

7 The position of a gene on a particular chromosome is its locus.

8 A gene found on the X chromosome but not on the Y chromosome is known as a sex-linked gene.

9 The genotype of an organism showing dominant characteristics can be determined by looking at the off spring produced when it is crossed with an organism showing recessive characteristics. This is called a test cross.

10 Monohybrid crosses consider the inheritance of one gene. Dihybrid crosses consider the inheritance of two diff erent genes.

11 The χ2 test can be used to find out whether any diff erences between expected results and observed results of a genetic cross are due to chance, or whether the difference is significant.

12 The genotype of an organism gives it the potential to show a particular characteristic. In many cases, the degree to which this characteristic is shown is also affected by the organism’s environment.

13 Mutation can be defined as an unpredictable change in the base sequence in a DNA molecule (gene mutation) or in the structure or number of chromosomes (chromosome mutation). New alleles arise by gene mutation. Gene mutations include base substitutions, deletions or additions. The HbS (sickle cell) allele arose by base substitution. Such mutations may affect the organism’s phenotype.

1. End-of-chapter questions

1. A cell in the process of meiosis was seen to have a spindle with sister chromatids being drawn towards opposite poles of the cell. In what stage of meiosis was the cell? .
A anaphase I
B anaphase II
C metaphase I
D metaphase II

2 All the offspring of a cross between pure-bred red-flowered and pure-bred white-flowered snapdragons were pink.

Two of these pink-flowered plants were interbred. What proportion of the offspring were pink?
A 25%
B 33%
C 50%
D 100%

3 A man has haemophilia. Which statement correctly describes the inheritance of the gene causing his condition?

A He inherited the recessive allele from his mother.
B He inherited the dominant allele from his father.
C He can pass the recessive allele to a son.
D He can pass the dominant allele to a daughter.

4 The diploid (2n) chromosome number of Drosophila is 8. Copy and complete the table to show the different outcome of mitotic and meiotic division of a Drosophila cell.

5 Copy and complete the table to compare meiosis with mitosis.

6 a Describe the essential difference between meiosis I and meiosis II.

b State the similarity between meiosis II and mitosis.

7 There is no crossing over during meiosis in male Drosophila. Assuming that no mutation occurs, the only source of genetic variation is independent assortment. Given that the diploid (2n) chromosome number is 8, calculate the number of genetically different spermatozoa that can be produced.

8 Distinguish between the following pairs of terms.

a genotype and phenotype

b homozygous and heterozygous

9 In sweet-pea plants, the gene A/a controls flower colour. The dominant allele gives purple flowers and the recessive allele red flowers.

A second gene, B/b, controls the shape of the pollen grains. The dominant allele gives elongated grains and the recessive allele spherical grains.

A plant with the genotype AaBb was test-crossed by interbreeding it with a plant with red flowers and spherical pollen grains.

Copy and complete the table to show that the expected ratio of phenotypes of the offspring of this cross. The gametes from one parent are already in the table.

[5]

10 a The fruit fly, Drosophila melanogaster, feeds on sugars found in damaged fruits. A fly with normal features is called a wild type. It has a striped body and its wings are longer than its abdomen. There are mutant variations such as an ebony-coloured body or vestigial wings. These three types of fly are shown in the figure.

Wild-type features are coded for by dominant alleles: A for wild-type body and B for wild-type wings. Explain what is meant by the terms allele and dominant. [2]

b Two wild-type fruit flies were crossed. Each had alleles A and B and carried alleles for ebony body and vestigial wings.

Draw a genetic diagram to show the possible offspring of this cross. [6]

c When the two heterozygote flies in b were crossed, 384 eggs hatched and developed into adult flies.
A chi-squared (X2) test was carried out to test the significance of the differences between observed and expected results:

i Copy and complete the table.

[1]

ii Calculate the value for X²

The table below relates X² values to probability values.
As four classes of data were counted, the number of degrees of freedom was 4 - 1 = 3. The table gives values of X² where there are three degrees of freedom.

iii Using your value for X² and the table above, explain whether or not the observed results were significantly different from the expected results. [2]

[Total: 14]

[Cambridge International AS and A Level Biology 9700/41, Question 7, October/November2009]

2. End-of-chapter answers

1 B
2 C
3 A