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Flashcards in Genes And Environment Deck (12):

List the main environmental factors that influence gene expression

• Temperature
-Siamese cat
• Light
-Arctic hare
-Human mood
• Chemicals
-Conditional nutritional mutations
(ACE, PKU, Porphyria)
-Dietary sensitivities
(Diabetes, obese, FTO)
• Age
-Huntington’s, cancer, heart disease
• Incomplete penetrance as a result
-Huntington’s, Hare lip, dog spots


What is a conditional mutation?

Phenotype depends on the environment


Give examples of how temperature can influence gene expression

Siamese cat
• Fur colour determined by mutation in melanin gene
• In cooler parts of body, enzyme works (eg. Ears), but deactivated in warmer parts

• Temperature sensitive allele can lead to dark eyes in cold larvae and light in warm


Give examples of how light can influence gene expression

Arctic Hare:
• Short periods of light exposure detected by cryptochrome photoreceptor- melanin action turned off
• Dark fur in summer, light in winter

• Also sensitive to day length (cryptochrome molecules)- lose leaves in Autumn

• Mood dependant on day length due to mutations in circadian genes


Outline ACE

ACE- Angiotensin converting enzyme
• Converts angiotensin I to angiotensin II- causes vasoconstriction- increased BP
• Homozygous insertion (II) in Intron 16 of ACE gene better climbers and trauma survivors


List the examples for chemical effects on gene expression

E.coli tryptophyan
-Leiden allele
Dietary sensitivities
-type II diabetes
-obese mice
-human leptin mutation


Give examples for conditional nutritional mutations effects on gene expression

• Some mutants unable to grow without tryptophan amino acid- unable to synthesise

PKU- Phenylketonuria
• PAH gene on chromosome 12
• Lack phenylalanine hydroxylase, can’t convert phenylalanine to tyrosine
• Heterozygote advantage- protection against ochratoxin A fungal toxin
• Builds up to toxic levels
• Heel prick bacteria test
• Treatment by dietary restriction

• Inability to break down haemin- porphin builds up in skin- light sensitivity, mental decay, dark red urine


Define Pharmacogenetics

Genetic effects on drug metabolism


Give examples of Pharmacogenetics

• Barbiturates lethal to porphyria people- same breakdown pathway

• Codine-> morphine, 10% population unable to convert

• Leiden blood group allele and old contraceptive pill combination- increased thrombosis risk


Give examples of genetic dietary sensitivities

• Type II diabetes risk associated with weight

• Obese mutation in mice- lack leptin satiety hormone- keep eating

• Human leptin mutations- treated with leptin injections

• FTO- fused toes in mice, increased hunger in humans. Gene expressed in brain but AA on average 2kg heavier than TT


Give examples of how age can influence gene expression

• Huntington’s disease dominant but only in over 50s
• Cancer and heart disease genes are also expressed later in life


Define incomplete penetrance

When a particular gene doesn’t manifest effects in all