Sequence & Gene Mutations Vocab

Mutation

Change in the DNA sequence, anywhere!!!

mutant allele

Variant of a gene associated with disease OR that occurs in less than 1% of the population

Polymorphism

Less than 1% of population and no known disease association

• Single Nucleotide Polymorphisms (SNPs)

How do new traits arise?

Random or because an organism NEEDS to adapt?

• Variation required for natural selection to act

6 Different ways to classify mutations

1. Type of cell affected

2. Change to DNA sequence

3. Change to gene function

4. Change to protein coding sequence

5. Effect on phenotype

6. Causes

1. Type of cell affected

Germline Vs Somatic

2. Change to DNA sequence

• Change in a single base pair can result in Base substitution/point mutation (Transition or transversion)

• Insertions or Deletions in nucleotides

3. Change to gene function

Neutral

gain of function

loss of function

4. Change to protein coding sequence

-Silent

-Missense

-nonsense

-frameshift

5. Effect on phenotype

Dominant or recessive

6. Causes

Endogenous-Spontaneous

Exogenous- Induced

Somatic mutation

A mutation that occurs in the body cells. Cannot be inherited.

Germline mutation

DNA alteration occurring in gametes that can be transmitted to offspring

Transition:

Change of pyrimidine (C,T) to another pyrimidine or a purine (A,G) to another purine

Transversion:

Change of a pyrimidine (C,T) to a purine (A,G) or vice versa

Neutral mutation

a mutation that has no effect on survival or reproduction

Gain of function mutation

Gene product does something extra; usually dominant on phenotype, one mutant allele required

Loss of function mutation

Complete loss or decrease in function of a gene product; recessive effect on phenotype, two, copies of the mutant allele required

Silent mutation

Base substitution that DOES NOT alter the amino acid sequence of the polypeptide; redundancy within genetic code

Missense mutation

Base substitution that DOES alter the amino acid sequence, can be neutral or harmful

Nonsense mutations

Base substitution that changes a sense codon to a STOP codon

Frameshift mutation:

Insertion or deletion of a number of nucleotides NOT divisible by three

• Shifts the reading frame

Causes of Endogenous (spontaneous) mutations

Result from abnormalities in cellular/biological processes (e.g., byproducts of metabolism, depurination, and errors in DNA replication)

Exogenous (Induced) mutations-

Result from chemical or physical agents (mutagens)that alter DNA structure (e.g., UV light, thymine, dimers, deletions)

Mutagen

Mutation generator

Endogenous Mutations ( 3 types of changes to nitrogenous bases)

1. Depurination

2. Deamination

3. Tautomeric shift

Depurination

Result of endogenous DNA damage due to by products of metabolism.

loss of a purine nitrogenous base

Deamination

Removal of an amino group from a cytosine base

Result of endogenous DNA damage due to by products of metabolism.

Tautomeric shifts: (Temporary shift in a nitrogenous base)

spontaneous rearrangement of hydrogens in a nitrogenous base

Exogenous Mutation (caused by mutagens) May Alter DNA Structure in Different Ways

Chemical mutagens come in three main types

Physical mutagens can come in two main types

Chemical mutagens come in three main types

1. Base modifiers - modify nitrogenous bases in different ways

2. Intercalating agents - insert between "rungs" of DNA double helix*

3. Base analogs - similar structures to natural nitrogenous bases

Physical mutagens can damage DNA and come in 2 main types

1. Ionizing radiation (e.g., X-rays, gamma rays)

2. Nonionizing radiation (e.g., UV light) - cross-linked thymine dimers*