Topic C

Question 1

What was known at the time of Beadle and Tatum’s research (1940s)

Answer 1

A gene is the fundamental unit of heredity inherited according to Mendel’s two laws

Genes are located on chromosomes (Morgan)

Enzymes catalyze chemical reactions

Biochemical pathways

Inborn errors of metabolism (deficiencies in biochemical pathways can be hereditary)

——————-

One Gene (fundamental unit of heredity)
l
V
One Enzyme❌
One Polypeptide✔️

Question 2

Building Biochemical Pathways and Identifying Where Mutant Strains Are Blocked

Question 3

Complementation

Answer 3

• Proteins, Enzymes, Polypeptides
• Multi-subunit proteins
• Multiple polypeptide subunits = multiple genes

If a cross between strains restores function:
- Complementation has occurred
-Mutations are non-allelic

If a cross between strains does not restore function:
- Complementation has not occurred
- Mutations are allelic

Question 4

Complementation

Genes and alleles

Answer 4

Genes and alleles
- A gene is the fundamental unit of heredity
- Alleles are sequence variants of a gene
- A gene can have many different alleles
- A diploid individual will have two alleles of a gene

Homozygous vs. Heterozygous
- Dominant vs. Recessive alleles
- Dominant = the allele determining the phenotype in the heterozygote
- Recessive = the allele not determining the phenotype in the heterozygote
Gene A – Allele A

Question 5

When is a complementation test used?

What is a complementation test?

What is complementation?

Answer 5

A complementation test is used to determine if two mutants with the same phenotype have allelic or non- allelic mutations.

Two mutants are crossed to produce diploid progeny and we observe the phenotype of the progeny for complementation.

The production of a wild-type phenotype in the diploid progeny of two recessive mutants

Question 6

Complementation Test steps

Answer 6

1. Carry out each possible cross to obtain diploid
2. Observe the results
   - + indicates growth on minimal media (wildtype phenotype)
   - - indicates no growth on minimal media (mutant phenotype)
3. Draw conclusions

If a cross between strains restores function:
- Complementation has occurred
- Mutations are non-allelic

If a cross between strains does not restore function:
- Complementation has not occurred
- Mutations are allelic