THE GENE

Beedle and Tatum (1940) Experiments using the red bread mould Neurospora crassa.

• This mould has the advantage of being a haploid individual so all the genes are expressed. Different individuals can be separated because the spores form in long thin “pods” called ascs.

• Its requirements are simple.

• It grows quickly and produces results in a few days.

Producing mutant strains

Alter the genes by mutation and you will alter the dietary requirements.

Cross breeding strains

If four of the daughter spores give rise to colonies that are like the deficient parent and four give colonies that are like the wild type parent:

• The condition is hereditary

• It is caused by the mutation of a single gene

This is the pattern that Beedle and Tatum found

Conclusion

Enzymes are needed by this mould to synthesise vitamins and amino acids.
The production of these compounds is affected by mutation.
The inheritance pattern of these defective enzymes is the same as that of single genes.

Enzymes are proteins, but not all proteins are enzymes. They are all affected by mutations in the same way

Some proteins are made of subunits each of which is independently affected by mutations (eg haemoglobin has 2 alpha subunits and 2 beta subunits).

© Paul Billiet 2008