Gene And Environment Interactions Flashcards
Temperature
Siamese cat, fur colour determined by a mutation in the melanin gene
In parts of the body such as the ears the enzyme that makes melanin (tyrosinase) works
However the enzyme is deactivated in warmer parts of the body such as the main body
Another example of a temperature sensitive mutation is white blood which effects eye colour in Drosophilia
Light
Arctic hare; lives at northern latitudes; summer has dark fur; winter has light fur. Adaptation
to camouflage. Opsin genes. Short periods of light exposure turn off melanin action.
Plants also sensitive to day length; loose leaves in autumn; cryptochrome molecules determine the
length of day.
In humans, mutations in circadian genes alter their mood dependent upon day length, SAD. Also explains why we feel so rotten due to jet lag.
Chemicals: angiotensin
Angiotensin is a peptide hormone that causes vasoconstriction and a subsequent
increase in blood pressure. Effects oxygen uptake. ACE loci has 2 alleles: Insertion (I) 287bp long and
Deletion (D) allele. Genotypes: II, ID and DD. II individuals more likely to survive trauma, be
successful mountain climbers and respond better to physical training than DD individuals. Another
example, ACTN3 variants effect success in power sports.
Chemicals : nutritional conditional mutations
In bacteria; can grow only on certain foodstuffs. E. coli can
normally grow on medium lacking the amino acid tryptophan because they can synthesise them.
Some mutants are unable to do this and fail to grow. Analogous to the emergence of antibiotic
resistance.
Chemicals : Phenylketonuria (PKU)
Amino acid sensitivity in humans (PAH gene). Homozygote recessive individuals cannot break down phenylalanine and the build-up of metabolic intermediates can be
lethal. Individuals must eat a highly controlled diet which does not contain phenylalanine.
Chemicals: porphyria
George III developed abnormal mentality; probably had porphyria.
Cannot break down haemin and build up porphyrin.
Diagnosed by dark red urine.
Light sensitive mutation and the disease can be
controlled by avoiding light.
Chemicals: pharmacogenetics
Genetic effects on drug metabolism; individuals respond differently to drugs. In South Africa, some individuals have a mild form of porphyria have lower lethal doses barbiturates
than individuals without the porphyria mutation. Individuals with the Leiden allele were more
susceptible to thrombosis from an early version of the contraceptive pill.
Chemicals; Dietary sensitivities
Obesity has become a global epidemic. In America the problem is major but is
also a socioeconomic issue; poor areas are more obese. The UK is one of the fattest countries in
Europe.
Chemicals: sugar
Causes type II diabetes; an inability to absorb sugar in the blood leading to high blood sugar
content which can cause, for example, brain damage and kidney damage. Risk is associated with
weight in both males and females.
Does weight have a genetic component
Obese mutation in mice was early evidence; inability to know when to stop eating.
Lacks leptin satiety hormone, so they never feel fill up. Humans can have mutations in leptin which is treated using leptin injections
Fused Toes (FTO)
TO (Fused TOes) developmental gene; in mice, it is a skeletal mutation gene which causes fused
toes; in humans, it makes you hungry AA (homozygous for FTO mutation) are hungrier and weigh more than AT and TT individuals.
Age
Many genes show phenotype only after a certain age. Huntington’s Disease dominant; but only
if consider over-50s; does not show effects in many younger carriers. Cancer and heart-disease
genes ditto.
Expressivity and penetrance
Environmental effects often confuse pedigrees. E.g. identical twins, one with and one without hare lip.
Often great variation in extent of manifestation of a particular gene - e.g. dominant spotting in
cats (variation in expressivity).
Sometimes, an individual who must have carried a gene - given parents and offspring - a particular gene does not manifest its effects at all; incomplete penetrance.
