Download 3 - misslongscience

3.1.6 Reproductive choices
The context
The contexts for this topic are inherited diseases and the limited technologies that can be used to
avoid their inheritance. It considers the way in which genetic information allows people to make
choices and how they can be supported in making these choices.
• Patterns of inheritance of single gene diseases. The more complex roles of several genes plus
the influence of the environment in determining the risks of diseases such as cancer and heart
disease.
• Antenatal testing and screening; the techniques of amniocentesis and CVS, blood tests and
ultrasound scans. The reliability and interpretation of the information obtained.
• Screening for inherited diseases; the advantages and disadvantages for families and for society.
• The use of IVF and PGD; benefits and differing views on some of the potential applications
• Genetic counselling, the role and responsibility of counsellors in providing information and in
helping people make decisions.
The science
In this context candidates are expected to show that they understand the following by using the
concepts to interpret information and to make predictions. They should be able to explain the
science in a way that might be used by a genetic counsellor.
• Instructions for development are found in the form of genes which are part of the chromosomes
in the nucleus of every cell in the organism. Each gene is a segment of a very long molecule of
DNA. Chromosomes contain a large number of genes. All cells except sex cells, and red blood
cells, contain two sets of chromosomes. Both chromosomes in a pair carry the same genes in the
same place, but the two chromosomes may carry slightly different versions, called alleles.
• In sexual reproduction, a single specialised cell from a female merges with another specialised
cell from a male. Each of these sex cells contains a randomly selected half of the parent’s genes.
The single cell which they form then contains a full set of genetic information, one of each gene
pair coming from a different parent. This process means that there is a very large number of
possible combinations of the parents’ genes, so offspring can be quite varied in their
characteristics. As a new organism grows from a single cell, its full set of genes is replicated in
each cell.
• In any cell only a fraction of all the genes are expressed, that is, determine the functioning of the
cell. The genes that are not expressed have no influence on the cell.
• Each cell contains two genes with the same function, and each gene may occur in two or more
different versions called alleles. The way one allele affects cell function may dominate the effects
of other alleles. This allele is known as dominant, and the others as recessive alleles. The effects
of recessive alleles are only seen if both chromosomes carry the recessive alleles.
• Most characteristics are determined by an interaction between several genes as well as by the
effect of the environment. The environment can influence gene expression.
• In addition to the variation which arises through sexual reproduction, change can occasionally
happen to a gene itself. This is called mutation. It can be caused by certain chemicals, by ionising
radiation (including ultraviolet rays, X-rays or gamma rays). If a mutated gene happens to be in a
sex cell, copies of it can be handed on to an offspring, perhaps giving it new characteristics. These
may be undesirable or beneficial, or have no effect on the offspring’s ability to survive and
reproduce.
How Science Works
In this context candidates should be able to use these ideas to discuss decision-making, to
analyse an argument on the issue and to develop and argue a personal position on the issues.
• Science-based technology provides people with many things that they value, and which enhance
the quality of life or of the environment. Some technologies, however, have unintended and
undesirable impacts. These need to be weighed against the benefits.
• Decision makers are influenced by the mass media, by special interest groups and by public
opinion as well as by expert evidence. Decisions about science and technology may be influenced
by decision makers’ prior beliefs or vested interests, which can affect their interpretation and
evaluation of the evidence.
• Some new technologies and new areas of scientific research raise ethical issues. That is to say,
they raise questions about whether a particular action is right or wrong.
• Decisions and opinions on ethical issues are based on values. An individual’s view on an issue
may be based upon a religious or moral position.
• Some decisions involve balancing the rights of certain individuals and groups against those of
others.
• A utilitarian approach is to argue that the right decision or choice is the one that leads to the
greatest good for the largest number. It can also be argued, however, that some actions are
wrong, even if they lead to good outcomes.
• Scientists have an individual responsibility to ensure that their practice is ethical. This may be
detailed in a professional ethical code. Such codes may also form the basis of regulatory decision
by ethics committees. National or international regulations that apply to scientific activity may have
an ethical basis.