DNA is a very stable molecule and, under the right conditions, and in certain tissues, it can remain intact for a very long time. For example, DNA in bones or hair can remain intact for hundreds of years. Armed with these new techniques for DNA analysis, archaeologists and anthropologists are able to analyse samples of DNA extracted from ancient corpses, such as the Egyptian mummies. The results obtained in these studies are providing information about the relationships between the different races of humans, and about human evolution.
3 The diagram above represents a gene located in
a section of DNA that a forensic scientist wants to analyse. Only one strand of the DNA is shown. The code for the gene is shown in red.
To cut up the DNA, a restriction enzyme that recognises a particular sequence of six bases is to be used. The restriction enzyme uses the base sequence GATATC to allow it to identify the place where the DNA should be cut.
a Copy the base sequence shown above and identify each location where the restriction enzyme
will attach to the section of DNA for cutting.
b Propose reasons why this particular restriction
enzyme was chosen to locate the place to cut the DNA.
c Construct a sequence of six bases for a gene
probe that will attach to the gene shown in the diagram.
4 It has recently been suggested that the use of DNA
for crime solving might have serious flaws. The technology is now so freely available that a criminal could potentially take someone else’s DNA, use a PCR (polymerase chain reaction) to make lots of it, and then deliberately spread it around at a crime scene.
a Conduct research to find out how DNA is
replicated using PCR.
b Produce a poster or cartoon to demonstrate how
a sample of DNA can be replicated by PCR.
c Using an example, assess whether criminals using
this technique could influence the use of DNA as evidence of their crime.
5 Imagine you are in a small town where a serious
crime has been committed. In order to help catch the criminal, the police have asked everyone to give a DNA sample for analysis. This would either eliminate people as suspects or, hopefully, confirm the criminal’s identity.
A A T G C G T C T G A T A T C T C C CA T G C A C G C G C C C G G G A T T A C G T A C C C G G G A T C C G C G T A AC A C T G A T A T C T A T T
a Discuss whether giving a DNA sample should
be voluntary or compulsory.
b A person has chosen not to give a DNA sample
as they fear their genetic information may be misused. Account for this person’s decision.
c Do you think that a person who chooses not
to give a DNA sample should be treated any differently than a person who does give one?
Justify your answer.
d Propose a set of guidelines that could be used
when collecting DNA samples for analysis in this town, to convince people that their DNA would not be misused.
Fig SF 4.7
Police collect DNA using a cottonbud-like swab and seal the sample in a tube for testing. A swab to collect cells is usually taken from the inside of the cheek.
Chapter review
[Summary questions]
1 List two influences that make you what you are, giving
an example of each.
2 a List two ways in which you resemble your mother. b List two ways in which you resemble your father. c List any of your own characteristics that are like
those of your grandparents and not like your parents.
3 In Mendel’s pea plants, long-stem flowers were
dominant over short-stem flowers. Stem length is controlled by a single gene with dominant and recessive alleles. Using this example, explain what is meant by the following terms:
a allele b genotype c phenotype d homozygous e heterozygous
4 a Define the term ‘gene’.
b State what the letters DNA stand for. 5 Distinguish between genes, chromosomes and
DNA.
6 For each term in the table, identify the relevant
description.
7 Use examples to explain the difference between
dominant and codominant inheritance.
8 Using examples, explain the difference between
continuous and discontinuous variation within a population.
9 Briefly outline the process of replication of DNA.
10 For each term in the table, identify the relevant
description.
11 Explain what is meant by:
a gene technology c gene cell therapy b cloning d therapeutic cloning 12 a State three arguments for the use of genetically
modified foods.
b State three arguments against the use of genetically
modified foods.
[Thinking questions]
13 Select the statements from i to v that are correct for: a mitosis
b meiosis
i It involves replication of DNA strands. ii Two daughter cells are produced. iii Four daughter cells are produced.
iv It produces cells with half the chromosome number
of the parent cell.
v It occurs in most body cells.
14 The ability to taste a bitter chemical known as PTC is
dominant over the inability to taste it. Three children in a family can taste PTC; one cannot. Explain whether it is possible for both parents to be:
a non-tasters of PTC b tasters of PTC Term Meiosis Mitosis Diploid Haploid Gene DNA Description
Chemical that carries the genetic code A hereditary unit
Cell division that produces gametes Cell division that produces daughter cells identical to the parent cell
A cell that has two of each type of chromosome
A cell that has one of each type of chromosome
Description
Causes a spontaneous change in a gene or chromosome A small piece of DNA that recognises a gene
An organism with a new gene Shows the positions of genes on chromosomes
A circular piece of DNA A molecule containing DNA from two organisms
A sequence of three bases that codes for an amino acid
Term Codon Genetic map Plasmid Gene probe Recombinant DNA Transgenic organism Mutagen
1 1 2 2 1 2 3 I II III IV
15 Colour blindness is an X-linked recessive disorder. The
symbols used to show the relevant genes are Xn for
the recessive gene on the X chromosome and XN for
the normal gene on the X chromosome. A colour-blind female partners a non-colour-blind male.
a State the two possible genotypes of their offspring. b Their daughters will be carriers of the disorder.
Explain what this means.
16 The structure of DNA may be likened to that of a twisted
ladder. State:
a what forms the uprights of the ladder b what forms the rungs of the ladder
c the name given to the structure formed when the
ladder is twisted
17 Explain how a mutation may be:
a harmful to an individual but have no effect on the
species
b harmful to the species but not to the individual c beneficial to the species
18 a State the approximate percentage of your total
DNA base sequence that is the same as that of your classmates.
b State whether it is possible for two people to have
exactly the same total DNA base sequence. Justify your answer.
[Interpreting questions ]
19 In humans the ability to roll the tongue (R) is dominant
over the allele for being unable to roll the tongue (r). A tongue-rolling heterozygous person is crossed with a person who cannot roll their tongue.
a State the genotype of each person.
b State the possible genotypes of their offspring. c Predict the percentage of offspring that would be
expected to have each of the genotypes listed in b.
d Predict the possible phenotypes of the offspring. e Predict the percentage of offspring that would be
expected to have each of the phenotypes listed in c.
20 For snapdragons, a cross between a plant with red
flowers (RR) and a plant with white flowers (WW) produces a plant with pink flowers. Predict the expected ratio of red, white and pink flowers in the offspring of a cross between:
a a red-flowered plant and a pink-flowered plant b two pink-flowered plants
Worksheet 4.6 Genetics crossword
Worksheet 4.7 Sci-words
21 The father of a child has blood group AB; the mother
has group O. Predict the possible blood groups of the child.
22 Albinism is caused by a single recessive gene (a). Two
people heterozygous for albinism produce a child.
a Predict whether the parents are albino.
b Predict the chances that the child will be albino. 23 A pedigree for a rare X-linked disease is shown in
the figure below. The symbols used to show the relevant genes are Xm for the recessive gene on the
X chromosome and XM for the normal gene on the
X chromosome.
a State the genotypes of the following individuals: i II male 3
ii the female partner of II male 3 iii III male 1
b Is the disease carried by a dominant or a recessive
gene? Justify your answer.
c Predict the probability that a male child of female
III 2 and her partner will have the disease.
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By the end of this chapter you should be able to:
explain the terms ‘speed’, ‘acceleration’, ‘force’ and ‘energy’ contrast Newton’s Laws of Motion analyse motion using Newton’s
Laws
explain how gravity and air resistance affect falling objects sketch graphs that illustrate
various motions
calculate speed, force and energies.
1 Where would feathers and hammers fall at the same rate?
2 How long does it take you to react to something?
3 Passengers are thrown forward in a head-on car crash. True or false?
4 Are headrests in cars for comfort or for some other reason?
5 What are the differences between kicking a football and kicking a brick?
6 How does a jet engine propel an aircraft forward?
7 How can the footballer in the photo still be moving if his feet are not touching the ground?
8 Why is motion often blurred in photos?