1. LECTURE 5: HUNTING FOR MUTANTS

2. What is a mutant?
A mutant is different than “normal”.
The mutant characteristic is passed
on to the next generation.

3. Central Dogma of Biology
DNA -> RNA -> Protein
DNA
mRNA
Transcription
Translation
Protein
Gene Function

4. Mutations Often Result in the Synthesis of Abnormal Proteins
DNA
mRNA
Transcription
Translation
Protein
DNA -> RNA -> Protein X
Abnormal Gene Function

5. Mutation of the Fly dpp gene

6. Mutation of the Fly dpp gene

7. Recessive versus Dominant Mutations/Alleles
Allele: A particular variant of a gene (could be normal
or mutant).
Recessive mutations: Both copies of the gene must
be mutated to manifest defect (homozygous).
Loss-of-function mutations are typically recessive.
Recessive mutations are represented by lower case letters.
+ = wildtype, m = recessive mutation
Dominant mutations: The defect is manifest when
only copy of the gene is mutated (heterozygous).
Dominant mutations can confer new activities or interfere
with normal gene function.
Dominant mutations are represented by upper case letters.
+ = wildtype, M = dominant mutation

8. Genotype versus Phenotype
Genotype: The genetic make-up of an individual.
Examples: +/+, +/m, m/m, +/M
Phenotype: The appearance of an individual.
Example: Individuals having a +/+ or +/m genotype have a normal phenotype.
Individuals having m/m genotype have mutant phenotype.
Individuals with one normal (+) and one mutant (m) copy of a gene are called carriers for the mutation (+/m).

9. Abe Lincoln

10. One quarter of the offspring from two Marfan carrier
parents will have Marfan Syndrome + mf
Two types of mother’s eggs
Two types of father’s sperm
+/mf
+/+
mf/+
mf/mf + mf or
+/mf
mf/+
= 1/2 offspring = Normal
+/+
= 1/4 offspring = Normal
mf/mf
= 1/4 offspring = Marfan

11. Putting Mutations Into Groups
A. Two Genes Function in a Common Process

12. Putting Mutations Into Groups
B. Two non-responding mutations in the same gene
Mutant m1
Mutant m*1
Signal lacking -> No response
Signal lacking -> No response m1
m*1
Signal lacking -> No response

13. Putting Mutations Into Groups
C. Two non-responding mutations in different genes
Mutant m1
Mutant m2
Signal lacking -> No response
Receptor lacking -> No response m1
Normal offspring + m2
Signal and Receptor present -> Response

14. The Body Plan of a Fly MaggotV
Head
Thorax
Abdomen
Tail
“Denticle” Hairs
Skin
Nervous System
(inside)

15. Fly Embryonic Patterning Mutants
Anterior-Posterior Patterning Mutants
Dorsal-Ventral Patterning Mutants