Download Model Genetic Organisms

A mutant is different than “normal”.
The mutant characteristic is passed
on to the next generation.
Central Dogma of Biology
DNA -> RNA -> Protein
DNA
Transcription
mRNA
Translation
Protein
Gene Function
Mutations Often Result in the
Synthesis of Abnormal Proteins
DNA -> RNA -> Protein
X
DNA
Transcription
X
mRNA
Translation
X
Protein
Abnormal Gene Function
Mutation of the Fly dpp gene
Mutation of the Fly dpp gene
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
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).
Abe Lincoln
One quarter of the offspring from two Marfan carrier
parents will have Marfan Syndrome
Two types of mother’s eggs
mf
+
Two types
of father’s
sperm
+
+/++
mf
+/mf
mf
+
mf
mf/+
+
+
mf/mf mf
mf
+/+ = 1/4 offspring = Normal
+/mf or mf/+ = 1/2 offspring = Normal
mf/mf = 1/4 offspring = Marfan
Putting Mutations Into Groups
A. Two Genes Function in a Common Process
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
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
The Body Plan of a Fly Maggot
D
Tail
Skin
P
A
Head
Thorax
Abdomen
V
Nervous System
(inside)
“Denticle” Hairs
Fly Embryonic Patterning Mutants
Anterior-Posterior Patterning Mutants
Dorsal-Ventral Patterning Mutants