4. The structure of DNA can be changed and such changes may be reflected in the phenotype of the affected organism.
The phenotype of an organism is its total appearance determined during development by an interaction between its genetic make-up (genotype) and the environment.
A genome is all of the genetic material (DNA) within a cell and is specific to each organism. Genomes influence nearly all the traits or phenotypes. The phenotypic appearance is therefore directly affected by gene expression. The extent of phenotypic differences depends on how different the DNA sequences are in individuals, but may also be influenced by the environment.
• Outline evidence that led to Beadle and Tatum’s ‘one gene-one protein’ hypothesis and explain why this was altered to the ‘one gene – one polypeptide’ hypothesis
Beadle and Tatum carried out experiments with red bread mould. The normal variety of mould can manufacture certain substances that it needs for living, including vitamin B1, B2, B4 and B12. The normal moult possesses specific enzymes that catalyse the different reactions that produce these vitamins.
Beadle and Tatum produced several varieties of the bread mould, each of which had a change in one of its genes. They tested these varieties and found that some had lost their ability to make vitamin B2 while others could no longer make vitamin B4 and so on.
The results obtained by Beadle and Tatum showed that a change in various genes of the bread mould resulted in the loss of different enzymes and the failure of specific products to appear. These results indicated that one gene controlled vitamin B2 production and a different gene controlled vitamin B4 production.
CHANGED GENE -> NO ENZYME -> NO REACTION -> NO VITAMIN
Beadle and Tatum concluded that different genes are involved in making different enzymes
