Genes And Environment

Question 1

List the main environmental factors that influence gene expression

Answer 1

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

Question 2

What is a conditional mutation?

Answer 2

Phenotype depends on the environment

Question 3

Give examples of how temperature can influence gene expression

Answer 3

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

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

Question 4

Give examples of how light can influence gene expression

Answer 4

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

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

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

Question 5

Outline ACE

Answer 5

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

Question 6

List the examples for chemical effects on gene expression

Answer 6

ACE
E.coli tryptophyan
PKU
Porphyria
Pharmacogenetics
-barbiturates
-coding->morphine
-Leiden allele
Dietary sensitivities
-type II diabetes
-obese mice
-human leptin mutation
-FTO

Question 7

Give examples for conditional nutritional mutations effects on gene expression

Answer 7

E.coli
• 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

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

Question 8

Define Pharmacogenetics

Answer 8

Genetic effects on drug metabolism

Question 9

Give examples of Pharmacogenetics

Answer 9

• 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

Question 10

Give examples of genetic dietary sensitivities

Answer 10

• 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

Question 11

Give examples of how age can influence gene expression

Answer 11

• Huntington’s disease dominant but only in over 50s

* Cancer and heart disease genes are also expressed later in life

Question 12

Define incomplete penetrance

Answer 12

When a particular gene doesn’t manifest effects in all