Inheritance (c)
Mutations and chromosomal
abnormalities
Unit 1
Sub-topic 8
Cell Function and Inheritance
Mutations and chromosomal abnormalities
Alterations in an organism’s genetic material, from a change in the sequence of bases to a
change in the number of chromosomes can have quite marked effects on that individual,
sometimes beneficial, sometimes detrimental. Some of these changes end up being passed
on through the generations.
Gene mutations
1 Note the meaning of the term mutation.
2a)(i) An alteration to the base type or sequence in a DNA strand is called a gene
mutation. Name the FOUR types of gene mutation, briefly describing what happens
in each.
(ii) Which of these are termed ‘frameshift’ mutations and which ‘point’ mutations.
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(iii) Explain why frameshift mutations are more likely to lead to the formation of a
protein that is greatly changed or non-functional.
b) Identify the type of mutation (insertion, deletion, substitution, inversion) in each of
the diagrams below.
l l l l l l l l l l l
A T C GGT A AC G G
l l l l l l l l l l l
A T C GG T A AC G G
l l l l l l l l l l l
A T C GGT A AC G G
l l l l l l l l l l l
A T C GGT A AC G G
-
l l l l l l l l l l
A T C G T A AC G G
-
l l l l l l l l l l l
A T C GT GA AC G G
-
l l l l l l l l l l l
A T C GGT A AA G G
-
l l l l l l l l l l l l
A T C GGC T A AC G G
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3 a) Note some of the features of mutations and mutant alleles.
b) Mustard gas and various types of radiation are mutagenic agents. What do such
agents do?
Chromosome abnormalities
4 a) What name is given to the process by which a spindle fibre fails during meiosis and
one or more of the gametes produced receives an extra chromosome?
Label the point that this happens on the diagram of meiosis.
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b) (i) If a normal human sperm fertilises an egg containing
an extra copy of chromosome 21, what is the diploid
number of the zygote formed?
2n =
(ii) Identify this abnormality on the karyotype.
(iii) What name is given to the condition suffered by a person who develops from an
abnormal zygote of this type?
(ii) What relationship exists between age of mother and incidence of this condition?
5 a) Identify the chromosome abnormality in each of these karyotypes and note the name
of the condition it causes beside it. Include a brief description of the condition.
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b) What do both these chromosome abnormalities have in common?
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Genetic Screening and counselling
A lot of information about human genetics can be revealed by constructing and studying
family trees for particular traits. This allows the pattern of a genetic disorder to be
charted from generation to generation allowing the risk of passing on such a trait to be
predicted. From this information, genetic counsellors can advise people of the probable
risk of passing on such a trait and screening can be offered.
1 Complete the table to show the list the characteristics of a family tree that would
enable a geneticist to recognise a pattern of inheritance and the rules that the
geneticist would apply when adding genotypes to such a family tree.
Type of
inheritance
Characteristics of family tree that
show a pattern for this
autosomal
recessive
autosomal
dominant
sex-linked
recessive
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Rules a geneticist would
apply when adding
genotypes
2 a) Identify which type of inheritance each of these family trees characterises and give
an example of the trait such a pedigree would be typical of.
A
B
C
male
male
female affected
female unaffected
b) Why is it not possible for the geneticist to add the genotypes of the younger
members of a family tree showing Huntington’s chorea?
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3 a) What is pre-natal screening?
b) Amniocentesis and chorionic villus sampling (CVS) both involve obtaining the karyotype
of the fetus.
(i) What type of disorders can be identified by both these techniques?
(ii) What are the benefits and drawbacks of CVS over amniocentesis?
4 a) Briefly explain why, unlike that of a single gene disorder, it is not possible to assess
the risk of inheriting a polygenic disorder by family tree analysis.
b) What alternative method of risk evaluation is employed?
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5 Name an inherited disorder than can be detected by post-natal screening, how it
is detected and the treatment for that condition.
6 What is the difference between genetic counselling and genetic screening?
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