3.1 Genes Flashcards
What is a gene?
A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic.
Where are genes located?
A gene occupies a specific position on one type of chromosome. This position is called the locus of the gene.
What are alleles?
Specific forms of a gene. So for example, blue and green are alleles of the gene for eye colour. The alleles occupy that locus for that gene, lots of animals have two copies of each chromosomes so normally there are 2 alleles present.
Alleles usually only differ from each other by one or two bases only.
What are SNP’s?
Single nucleotide polymorphisms - positions in a gene where more than one base can be present.
What are mutations?
Mutations are random base changes to a gene. Mutations help evolution. Ones that are helpful are passed on and ones that are lethal do not get passed on as the organisms die.
How is sickle cell anaemia caused?
This is due to a base mutation in the gene that codes for the alpha-globin polypeptide in haemoglobin. Instead of being GAG, in the sixth codon, it is GTG. This means each sixth codon is valine instead of glutamic acid. This change causes haemoglobin molecules to stick together in tissues with low oxygen concentrations. The bundles of haemoglobin molecules that are formed are rigid enough to distort the red blood cells into a sickle shape.
These get stuck in capillaries, blocking them and reducing blood flow. When sickle cells return to high oxygen concentrations the haemoglobin unsticks together and they return to their normal shape. These changes occur over and over again as the red blood cells circulate. This damages the membrane and the haemoglobin, giving the red blood cells a shorter life. The body cannot replace them fast enough and they become anaemic.
What is a genome?
The whole of the genetic information of an organism. Genetic information is contained in DNA, so a living organism’s genome is the entire base sequence of each of its DNA molecules.
What is the genome of a human?
The genome consists of the 46 DNA molecules that form the chromosomes in the nucleus plus the DNA molecule in the mitochondrion.
What is the genome of plants?
The DNA molecules of chromosomes in the nucleus plus the DNA molecules in the mitochondrion and the chloroplast.
What was the human genome project?
The Human Genome Project began in 1990. It’s aim was to find the base sequence of the entire human genome. The project drove rapid improvements in base sequencing techniques.
How do we sequence genomes?
1) DNA is sliced up.
2) Coloured fluorescent markers are used to mark the DNA copies. A different colour of marker is used for the copies ending in each of the four bases.
3) The samples are mixed together and all the DNA copies are separated in one lane of a gel according to the number of nucleotides.
4) A laser scans along the lane to make the markers light up.
5) An optical detector is used to detect the colours. There is a series of peaks of fluorescence corresponding to each number of nucleotides.
6) Computer deduces the base sequence
