Chapter 12: QUICK-CHECK answers

Chapter 12

Answers QUICK-CHECK questions

1 Identify the following statements as true or false.

a Restriction enzymes cut DNA molecules at random sites along their length.

False: Cuts made by restriction enzymes do not occur randomly, but occur at specific recognition sites along a double-stranded DNA molecule.

b The restriction enzyme Aha I produces DNA fragments with sticky ends.

False: The restriction enzyme Aha I produces fragments with blunt ends(see figure 12.5).

c Target DNA must be denatured before it can be located with aprobe.

True: Target DNA must be denatured (made singlestranded) before it can be located with a probe.The probe is singlestranded and it can pair with a complementary base sequence in the single-stranded target DNA.

d An enzyme that can act on human DNA would not be able to act onmouse DNA.

False: DNA has an identical composition in all living organisms and so an enzyme that can act on DNA from one source can also act on DNA from any other source.

2 Where does in situ hybridisation occur?

In situ hybridisation occurs at a normal location in a cell.In the case of DNA, for example, in situ hybridisation would take place at the chromosomal location of DNA within the cell nucleus.

3 Give an example of a vector.

Vectors are carriers used to transport particular compounds.Examples of vectors used to transport DNA into a cell include plasmids and modified viruses.

4 What raw materials are needed to build a DNA segment using a DNA synthesiser?

Raw materials needed to build a DNA chain using a DNA synthesiser include the four different kinds of nucleotides that differ in their base component, with the four different bases in nucleotides found in DNA being adenine, guanine, cytosine and thymine.

(Note: The statement above reflects a highly simplified version of the chemical synthesis of DNA. In reality, the chemical reactions that occur in a DNA synthesiser are very complex but the end result is the production of a linear chain of nucleotides joined in a particular order.)

5 a Name the starting point for making copy DNA (cDNA).

The starting point for making copy DNA (cDNA) is mRNA.

b Name the enzyme needed to make cDNA.

The enzyme needed to make cDNA is reverse transcriptase.

6 Give an example of a protein made by recombinant DNA technology.

Proteins made by recombinant DNA technology include:

  • rec human insulin
  • rec human growth hormone
  • rec human follicle-stimulating hormone
  • rec factor 8.

(See table 12.2.)

(Note: Other examples include rec human antithrombin, rec human lactoferrin and recombinant plasma proteins additional to factor 8, including rec factor IX and rec factor VIIa.

7 What is meant by the term ‘TGO’?

TGO means transgenic organism.This term refers to an organism that has had DNA from another species artificially added to its genome.

8 Give an example of a plant crop that:

a is a source of GM food in overseas countries

Genetically modified (GM) plants that are a source of food include corn and soya beans.

(Note: At present, some GM foods that are grown overseas are approved for consumption in Australia as ingredients of processed food; these include GM corn, GM soya beans, and GM potato. This is a changing field; for a recent update from CSIRO, see

b has been engineered to contain the Bt toxin gene.

The Bt toxin gene has been engineered into cotton that is grown in Australia.

9 Name the legislation that governs gene technology in Australia.

The Federal legislation is the Gene Technology Act 2000.In addition, Australian states have enacted complementary legislation, such as Victoria'sGene Technology Act 2001.

10 One method of introducing a foreign gene to a species is micro-injection of a fertilised egg. List one disadvantage of this procedure.

A disadvantage of micro-injection of a fertilised egg is that the procedure is unpredictable.The location where the injected foreign gene inserts is random and uncontrolled, and, in some cases, it may insert within an essential gene disrupting the function of that gene so that the egg does not develop.

11 If Jane’s fetus had shown a RFLP pattern identical with that in Tom, what conclusion may have been drawn about this fetus?

If Jane’s male fetus showed the same RFLP pattern as Tom, it would be reasonable to conclude that the fetus had inherited the haemophilia allele (c) from Jane and that it would be affected by this disorder.

12 What is meant by the term ‘predictive testing’?

Predictive testing refers to procedures used to test for the presence or absence of an allele responsible for an inherited disorder in a person who is at risk of having inherited that allele but who shows no signs of the disorder in their phenotype.

13 What does the abbreviation RFLP denote?

The abbreviation RFLP stands for restriction fragment length polymorphism.

14 If a person at risk of HD has 56 CAG repeats in one of the HD alleles, what conclusion can be drawn?

Based on the number of CAG repeats in this allele, it is reasonable to conclude that the person has inherited the HD allele that is responsible for Huntington disease from an affected parent.

15 Identify the following statements as true or false.

a The current technique of identification by DNA is known as DNAfingerprinting.

False: The current technique for identification by DNA is called DNA profiling and is based on detection of variation in regions of DNA known as short tandem repeats (STRs).

b A minisatellite is also known as a short tandem repeat.

False: A short tandem repeat can also termed a microsatellite. Minisatellites are another kind of variable region of DNA but they differ from microsatellites.

c The length of the repeated unit in an STR is from two to five base pairs.

True(Note: The label ‘short’ in STRs is in contrast to minisatellites where the repeating unit is typically much longer.)

d Chromosomal DNA gives more precise identification than mtDNA.

True: DNA profiles based on chromosomal DNA give far more precise identification than that obtained using mitochondrial DNA (mtDNA).Thisoccurs because mtDNA is inherited generation after generation without recombination from maternal ancestors, while STRs undergo reassortment during meiosis at every generation.So, in a large family extending across several generations, all members who share the same maternal ancestry will have identical mtDNA, but they will differ in many of their STRs.

e One person could have 10 different alleles at one STR locus.

False: While many different alleles are possible at each STR locus, a person can have at most only two alleles at each STR locus, one on each homologous chromosome pair.

16 List two differences between the techniques of DNA fingerprinting and DNA profiling.

DNA fingerprinting uses:

  • minisatellites
  • repeated sequences from 9 to 80 bases
  • regions with tens to hundreds of repeats
  • sites located at chromosome ends

DNA profiling uses:

  • short tandem repeats (STRs, also known as microsatellites)
  • repeated sequences from 2 to 5 bases
  • regions with commonly 5 to 20 repeats
  • sites located at loci within chromosomes

17 Who invented the technique of DNA fingerprinting?

Alex Jeffreys (now Professor Sir Alex Jeffreys) developed the technique of DNA fingerprinting in 1985.

18 Identify the following statements as true or false.

a The gender marker used in DNA profiling is an STR.

False: The gender marker is not an STR. The gender marker used is the Amel gene, and, unusually, this gene has a locus on both the X and the Y chromosomes.The size of the gene differs on each sex chromosome.As a result, a male with both an X and a Y chromosome shows two DNA bands for the gender marker, while a female with two X chromosomes shows just one marker.

b The national DNA databank in the United States is known as CODIS.

True: The national DNA databank set up by the FBI in the United States is known as CODIS (Combined DNA Index System).

c DNA profiling in Australia uses nine different STR loci.

True

19 What is the name of the national DNA database in Australia?

The national DNA data base in Australia is called CrimTrac.

20 A DNA profile shows two peaks for the gender marker. What is the gender of the person concerned?

If a profile shows two peaks for the Amel gender marker, this indicates the presence of both an X chromosome and a Y chromosome and so identifies the gender of the person concerned as male.

21 Give one example of the use of DNA profiling in assisting in a criminalconviction.

Examples include the conviction of Bradley Murdoch for the murder of Peter Falconio in Australia (see page 446) and the conviction of Francisco Montes for the murder of Caroline Dickinson in France (see page 447).

(Note: More recent high profile cases includee the conviction in 2007 of Glenn McNeill for the murder in March 2002 of Janelle Patton on Norfolk Island.)

22 List two non-human species for which DNA profiling has been done and, in each case, identify one reason why it was done.

Examples include:

  • DNA profiling of a cat was critical evidence in one case in Canada (see page 451).Cat hairs were found on a bloodstained jacket found near a crime scene and the blood matched that of the victim.The estranged husband of the victim was a suspect and so the cat hairs on this jacket were tested to see if there was a link to him.The DNA profile from the roots of the cat hairs identified the cat as one that the man had had contact with.This finding linked the bloodstained jacket to him and was part of the evidence that led to his conviction for murder.
  • In the USA, DNA profiling of human bloodstains and dog bloodstains on clothing worn by the accused matched that of the victims of a murder and their dog that was killed at the same time. This finding became part of the evidence that led to the conviction of the accused for murder.

23 Refer to figure 12.44 and identify the approximate size:

a of the gender marker for cats

The marker used as to identify gender in the DNA profiling of cats is the SRY marker on chromosome Y.This gender marker is just under 100 base pairs in length.

b range for the FCA740 marker in the cat population.

The FCA740 marker used in the DNA profiling of cats can range from about 310 to about 345 base pairs in length.

24 Identify one means by which tissue is obtained from dogs for DNA profiling.

Tissue for DNA profiling may, for example, be obtained from:

  • a buccal swab that contains epidermal cells (see figure 12.47)
  • a sample of hair (with roots)
  • a blood sample.

(Note:A DNA sample for profiling can be obtained from any biological material in which living cells are present. So, for example, a sample of dog saliva taken from the bitten area of skin of a person attacked by a dog could be used to implicate or exonerate a particular dog from the attack.)

25 Identify the following as true or false:

a Alleles at each STR locus behave in a Mendelian fashion.

True: The alleles at each STR locus are inherited in a manner identical to that of the alleles of any other autosomal gene.

b Boys inherit all their STR alleles from their fathers.

False: For every STR gene, each child, whether boy or girl, inherits one STR allele from themother and one allele from the father.

c DNA testing can be used to exclude a man as the biological fatherof a child.

True: In a case of disputed paternity, DNA testing has the power to exclude a man as being the father of a particular child on the basis of his DNA profile as compared with that of the child in question.

26 A mother with alleles 10 and 15 and a man with alleles 12 and 14 at the D8 STR locus could have a child with the alleles 14 and 15 at the same locus.

True: For the D8 STR marker, a child could inherit allele 15 from the mother and allele 14 from the father.

(Note:Other possible combinations are 10/12, 10/14 and 15/14.)

© John Wiley & Sons Australia, Ltd1