Mutations to Aid in Gene Study

By: Yvette MedinaCell Phys. 4454

Gene Mutation Summary

• Study of Gene Mutation can be useful in:– 1. the study of new genes required for the process– 2. the order in which gene products aid in the

process– 3. how different protein encodings are effected by

different gene interaction.

Quick definitions

• Alleles: variants of genes

• Mutation: a new form of an allele

• Mutagen: agent which causes heritable DNA sequence change

• Wild type: standard genotype in breeding experiments ( higher frequency of appearance)

Genotype versus Phenotype

• Genotype– 1. particular set of alleles

for all genes carried by an individual.

– 2. Alleles under examination

• Phenotype– 1. physical attributes of

traits of an individual due to genotype

– 2. the physical result of alleles under examination

Gene Function due to Mutant Recessive/ Dominant Alleles.

• Single set of chromosomes (Haploid)

• Two copies of each chromosome (Diploid)

– Homozygous: identical alleles

– Heterozygous: different alleles

• Dominant Mutation: loss of function of certain genes

• Haplo-Insufficient: both alleles are required for function

– Removing or inactivating a single allele

• Dominant Negative: structural change in a protein interferes with function of another protein on another allele

Cont’d• Recessive Mutant allele: both alleles are mutant and show mutant

phenotype– Results from inactivation gene– Leading to loss of function partially or completely– Remove part of the gene from chromosome– Disrupt expression of gene– Alter the encoded protein

• Dominant Mutant allele: one allele is wild type and the other is mutant– Cause gain of function– Increase the activity of encoded protein– Confer new activity– Lead to inappropriate spatial of temporal expression patterns

Chemical Enhanced Mutations

• EMS (ethylmethane sulfonate): common agent used for inducing mutations

• Ex. Chemical modification of Guanine G-C to A-T base pairs

• Point Mutations: alteration of the sequence of genes base pairs.

• Silent Point Mutation: no change of amino acid sequence or coded protein activity.

• Missense Mutation: substitution of one amino acid for another.

• Nonsense Mutation: introduction of premature stop.

• Frameshift Mutation: change in reading frame of gene.

Breeding reveals Dominance and Recessivity

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Isolate and Identify Mutants

• Genetic Screen: a simple procedure to identify and isolate Mutations which is dependent on haploid or diploid; recessive or dominant.

• Haploid Yeast Study-– Conditional Mutations:

Temperature-Sensitive Mutations: isolated in bacteria and lower eukaryotes.

Nonpermissive: temperature at which the mutant is phenotypically observed.

Permissive: Mutant phenotype is not observed but is present.

Complementation Tests for Same Gene Recessive

Mutations• Complementation: test used to

determine mutations are on the gene.

• Done by restoration of the wild type phenotype by mating two different mutants. – Two recessive mutations are on

the same gene, the diploid phenotype will show the mutation.

– If the mutation is on separate genes, diploid heterozygote phenotype will show the wild-type…complement.

Protein Function From Mutations

• Mutations for two different genes affect the same cellular process with distinct different phenotypes

• Double Mutants revel function order

• Can be used for Biosynthetic Pathways and Signaling pathways

Interacting and Redundant Proteins

• Suppressor Mutations: the function of one protein to suppress the function of another.

• Synthetic Lethal Mutation: mutation can be exacerbated by a

second mutation.

Summary

• Mutation can aid in identify different biological pathways function.

• Mutations are used to learn breeding patterns of genes

• Lastly the associated effects of mutations from one gene to

another.

• DNA Mutation Analysis