3.1 genes

gene

a unit of inheritance

a section of dna

gene locus

fixed position of gene on a chromosome

allele

different forms of the same gene

can have multiple alleles - eg. blood

diff alleles hv slight variation in base sequence

snps

single nucleotide polypmorphisms

alleles that differ by only 1 base

lead to variations in aa sequence

creates diversity

helps in dna fingerprinting

genome

the entire genetic info of an organism

eg. in humans, dna in nucleus (chromosomes) & mitochondrial dna

eg. in plants. chromosomes, chloroplast dna, mitochondrial dna

eg. prokaryotes, circular dna, plasmids

human genome project

aimed to discover complete set of human genes

benefits

• screening: dev of gene probes to detect sufferers & carriers of genetic diseases

• medical: discovery of new proteins, used to dev new treatments

discovered that most of the gene is not transcribed — mostly junk dna

mutations

completely random

new alleles formed

mutagens

increase likelihood of mutations

• ionizing radiation, gamma rays

• non ionizing radiation, uv rays

• chemicals, asbestos, tar

eg. sickle cell anemia (process)

dna: gag → gtg on non transcribed strand. creation of alleles Hbs → transcribed

mrna: gag → gug on 6th codon position → translated

polypeptide: 6th amino acid glutamic acid → valine on beta chain.

consequences

hemoglobin mols stick together in blood

form bundles → rigid → distort rbcs into sickle shape → block capillaries → restrict blood flow → damage tissues

only return to org shape in high o2 conditions in lung

changes occur again & again (repeat)

reduces lifespan of rbcs to 4 days

can cause anemia — rbcs cannot be replaced fast enough