Lecture 24

Question 1

The Alcohol dehydrogenase (Adh) polymorphism in drosophila:

Answer 1

• Alcohol is an external potentially toxic substrate
• Maps to 2:50.1
• Well known and studied
• Most activity is found in the fat body (the liver equivalent

Question 2

Selective neutrality:

Answer 2

• All genotypes are equally fit
• NS is not preferentially selecting one genotype over the other
• Effective population size and mutation rate are important for balancing and maintaining polymorphisms

Question 3

Clarke protocol and insecticide resistance:

Answer 3

1. Genetic variation must be shown to exist (2 alleles/allozymes, AdhF and AdhS)
2. Allele frequencies must be described over time in one population or through space across populations
3. Demonstrate phenotypic diversity among genotypes for an aspect of molecular function
4. Knowing the function of the gene product, the functional difference between the products of the alleles and the ecology of the organism, we should be able to postulate a relevant, discriminatory selective agent.

Question 4

AdhF and AdhS

Answer 4

• Two alleles AdhF and AdhS
• Due to the thermostability of the allozymes and their ability to move through a protein gel electrophoresis
• DNA sequencing revealed variation within the AdhF and AdhS allelic class

Question 5

F/S amino acid replacement effects what?

Answer 5

• Adh-S is lysine 192, a positive amino acid
• Adh-F threaonine 192, a neutral amino acid
• This is the difference in electrophoretic mobility.
• Is one fitter than the other?

Question 6

There is a relationship between AdhS frequency and latitude:

Answer 6

• There has been a decrease in AdhS frequency as you move away from the equator

Question 7

Geographical surveys detected a cline on five continents:

Answer 7

• Adhs fequency decreased moved from the equator

- An association with AdhS allele frequency and temperature in wineries

Question 8

ADH activity and substrates:

Answer 8

• There are a variety of alcohols in the drosophila environment
• Adh-F has a greater specific activity on primary alcohols like ethanol (it metabolises faster than S)
• Adhs has a higher relatve specificity to activity on secondary alcohols (eg, isopropanol)

Question 9

Primary alcohol:

Answer 9

• Gets converted to aldegyde with NAD is reduced to NADH

Question 10

Ethanol:

Answer 10

• Is converted to acetaldehyde with NAD being reduced to NADH
• Acetaldehyde is further metabolised into acetic acid (which is toxic)
• Build up of acetaldehyde results in mutagenesis of DNA

Question 11

Acetic acid is an energy source:

Answer 11

• Short term and longer term

Question 12

Isopropanol is converted into acetone

Answer 12

• This is converted with AdhS to a non-toxic compound

Question 13

ADH activity and temperature:

Answer 13

• ADH-S is more thermostable in extremely high temperatures (40degrees plus)
• At 40 degrees the flies are sterile, so this is not a realistic advantage
• At lower temperatures the reverse may be true

Question 14

ADH is required for:

Answer 14

• The utilisation and detoxification of ethanol in larvae and adults

Question 15

Drosophila are found in a range of environments:

Answer 15

• Temperature
• Type of alcohol
• Alcohol concentrations