Test Yourself
The Answers
Chapter Sixteen – Genetics Knowledge within an Ethical
Framework
1. Identify the four secondary principles reflected by the Human Genetics Commission
(DoH, 2002a) in the primary principle of ‘respect for persons’.

Principles of; privacy, consent, confidentially, non-discrimination.
2. Name the four nitrogen-containing bases of the DnA molecule.

Adenine, thymine, cytosine and guanine.
3. Describe the pairing rule of the nitrogen-containing bases in the DnA sequence.

A with T, and C with G. Adenine paired with thymine, and cytosine paired with
guanine.
4. Name the following conditions: (a) 47, XY+21, (b) 47, XXY, (c) 45, XO, (d) 12q24.1,
(e) Xq28.

(i) 47, XY+21 is a male individual with Down’s syndrome, so has an extra
chromosome at pair 21. It is classified as a chromosomal numerical condition – a
trisomy, caused by an error in cell division.
(ii) 47, XXY is a male individual with Klinefelter syndrome, so has an extra X
chromosome. It is classified as a chromosomal numerical condition – a trisomy,
caused by an error in cell division. In this condition it is an extra sex chromosome.
(iii) 45, X is a female individual with Turner syndrome, so only has one X
chromosome rather than the expected XX. It is classified as a chromosomal
numerical condition – a monosomy, caused by an error in cell division.
(iv) 12q24.1 is the karyotype for the condition Phenylketonuria (PKu). It is a
condition inherited in an autosomal recessive manner. This karyotype indicates
that the condition is inherited on an autosome (number 12) and the locus
(location) for the gene is at banding 24.1 and located on the q arm (long arm).
(v) Xq28 is the karyotype for the condition Major Affective Disorder (2). This
karyotype indicates that the condition is inherited on the X chromosome and the
locus (location) for the gene is at banding 28 and located on the q arm (long arm),
5. Define the terms: (a) autosomes, (b) trisomy, (c) monosomy, (d) non-disjunction.

(i) Autosomes: Pairs 1 to 22 of the chromosomes are called the autosomes. The
final pair (pair 23) is called the sex chromosomes (XX in the female and XY in the
male).
(ii) Trisomy: the presence of a complete chromosome, so gives the karyotype of
47 rather than the expected of 46.
(iii) Monosomy: the absence of a complete chromosome, so gives the karyotype of
45 rather than the expected 46.
(iv) Non-disjunction: failure of the chromosomes to split at the centromere, during
mitosis or meiosis.
6. Calculate the inheritance of a: (a) dominant condition, (b) recessive condition, (c) Xlinked condition.

(i) Inheritance of a dominant condition is 1:2 (50 per cent) risk/chance of an
offspring being affected.
(ii) Inheritance of a recessive condition is 1:4 (25 per cent) risk/chance of an
offspring being affected. 1:2 (50 per cent) risk/chance of an offspring being of
carrier status. 1:4 (25 per cent) chance of an offspring not being affected.