Genes

Nature of science:

Developments in scientific research follow improvements in technology—gene sequencers are used for the sequencing of genes. (1.8)

• A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic.
• A gene occupies a specific position on a chromosome.
• The various specific forms of a gene are alleles.
• Alleles differ from each other by one or only a few bases.
• New alleles are formed by mutation.
• The genome is the whole of the genetic information of an organism.
• The entire base sequence of human genes was sequenced in the Human Genome Project.

Applications and skills:

• Application: The causes of sickle cell anemia, including a base substitution mutation, a change to the base sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in hemoglobin.
• Application: Comparison of the number of genes in humans with other species.
• Skill: Use of a database to determine differences in the base sequence of a gene in two species.

• Sequencing of the human genome shows that all humans share the vast majority of their base sequences but also that there are many single nucleotide polymorphisms that contribute to human diversity.

Theory of knowledge:

• There is a link between sickle cell anemia and prevalence of malaria. How can we know whether there is a causal link in such cases or simply a correlation?

Aims:

• Aim 7: The use of a database to compare DNA base sequences.
• Aim 8: Ethics of patenting human genes.

• Students should be able to recall one specific base substitution that causes glutamic acid to be substituted by valine as the sixth amino acid in the hemoglobin polypeptide.
• The number of genes in a species should not be referred to as genome size as this term is used for the total amount of DNA. At least one plant and one bacterium should be included in the comparison and at least one species with more genes and one with fewer genes than a human.
• The Genbank® database can be used to search for DNA base sequences. The cytochrome C gene sequence is available for many different organisms and is of particular interest because of its use in reclassifying organisms into three domains.
• Deletions, insertions and frame shift mutations do not need to be included.