Gene and environment interaction Flashcards
(13 cards)
Give an example of a gene-temperature interaction
Siamese cat: Melanin gene mutation, when cool, tyrosinase enzyme works and melanin is produced, but this is deactivated in the warmer parts of the body. Also white blood which affects drosophila eye colour (cold red, warm white)
Give examples of gene-light interaction
Arctic hare; lives at northern latitudes; summer has dark fur; winter has light fur - camouflage. Opsin genes and cytochromes. Short periods of light exposure turn off melanin action. Similar mechanism for deciduous plants and human circadian rhythms
What are opsin genes
Opsin genes encode G-protein coupled receptors that initiate the phototransduction cascade, a mechanism by which light information is converted into an electrical signal to be interpreted by the brain.
What does the ACE locus code for and what is its effect?
Angiotensin is a peptide hormone that causes vasoconstriction and increased blood pressure. ACE loci has 2 alleles: Insertion (I) 287bp long and
Deletion (D) allele. II individuals more likely to survive trauma, be successful mountain climbers and respond better to physical training than DD due to Improved muscle efficiency, oxygen delivery, lower heart strain.
Give a bacterial example of gene-environment interaction
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.
What is Phenylketonuria?
PKU is caused by a PAH gene mutation. Homozygote recessive individuals cannot break down phenylalanine -> tyrosine, and the build-up of metabolic intermediates can be lethal - must eat a highly controlled diet. Linked to light skin/hair genes.
What genetic disorder did king George III have?
He probably had Porphyria - cannot break down haemin and build up porphyrin, due to a light-sensitive mutation. Causes mental abnormality and skin lesions as well as dark-red urine. Same pathway involved in barbiturate drug metabolism, some antidepressants more dangerous - important when porphyria frequency is high e.g. South Africa (Dutch founder effect)
Give an example of gene-chemical interaction
Women with the Leiden blood group allele were more at a heightened risk of thrombosis from an early version of the contraceptive pill.
Is obesity genetic/heritable?
Mutations in the gene coding for the hormone leptin can cause individuals to never feel full, can be treated with leptin injections. Homozygosity (AA) for the FTO gene (Fused TOes, expressed in the brain and affecting appetite) causes increased BMI than AT or TT.
What is incomplete penetrance?
A gene shows incomplete penetrance when someone carries it but displays no observable traits. For instance, a person with affected parents and offspring might appear unaffected themselves, masking the gene’s presence and complicating genetic analysis.
Difference between penetrance and expressivity
Penetrance describes whether a gene is expressed at all, while expressivity refers to how strongly it’s expressed. A gene can be fully penetrant but vary in expressivity, or it may not show at all in some carriers, demonstrating incomplete penetrance.
What is the importance of environmental effect in pedigrees?
Environmental factors can influence gene expression, making pedigree analysis complex. For example, identical twins with the same genetic makeup might differ in traits like a hare lip due to non-genetic factors affecting development in the womb or postnatally.
Define expressivity
Expressivity refers to the degree a gene is expressed in an individual. In dominant spotting in cats, all affected animals carry the gene, but the size and number of white patches can vary widely, showing how the same gene can have different visible effects.
