Key Knowledge:
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DNA is the genetic blueprint which codes for the characteristics of an organism (including physical, behavioural and physiological features)
- DNA is stored within the nucleus in eukaryotes and is found freely floating in the cytosol in prokaryotes (in a region called the nucleoid)
Gene
A gene is a heritable factor that consists of a sequence of DNA and influences a specific trait (i.e. a single genetic instruction)
- A gene determines a particular characteristic by coding for the production of a specific polypeptide (some traits require multiple genes)
Allele
Alleles are the alternative forms of a gene that code for different variations of a specific trait
- As alleles are different versions of a particular gene, they possess very similar sequences (only differ by one or a few bases)
Genome
The genome is the totality of genetic information of a cell, organism or organelle
- This includes all genes as well as non-coding DNA sequences (e.g. introns, promoters, short tandem repeats, etc.)
- The human genome consists of 46 chromosomes (barring aneuploidy), roughly 3 billion base pairs and around 20,000 genes
The Human Genome Project (HGP) was an international cooperative venture established to sequence the human genome
- The HGP showed that humans share the majority of their sequence, with short nucleotide polymorphisms contributing diversity
The completion of the Human Genome Project in 2003 lead to many outcomes:
- Mapping – The number, location, size and sequence of human genes is now established
- Screening – This has allowed for the production of specific gene probes to detect sufferers and carriers of genetic diseases
- Medicine – The discovery of new proteins have lead to improved treatments (pharmacogenetics and rational drug design)
- Ancestry – Comparisons with other genomes have provided insight into the origins, evolution and migratory patterns of man