Mutations

What is a mutation?

Any change in the DNA base sequence

What are the two different classes of mutations?

• Gene Mutations• Chromosomal Mutations

What is a gene mutation?

• A change in the base sequence of one gene

What causes gene mutations?

•Errors in DNA replication •Chemicals• UV/X-ray Radiation

Types of Gene Mutations• Substitution

• Deletion

• Insertion

Original DNA Strand

Two types of Gene Mutations

Point mutationA change in ONE nitrogenous base, the overall number of bases

stays the same (Substitution)

Frame shift mutationA change in the number of overall nitrogenous bases in the genetic

code (Insertion or Deletion)

Substitution Mutation• Substitution – One nitrogenous base is

substituted for another.

Deletion and Insertion Mutations• Deletion – One or more nitrogenous bases are

removed

• Insertion – Extra nitrogenous bases are added to the genetic code.

Sickle Cell Anemia

How does a mutated protein affect a cell?

•If the shape of the protein is altered, it MIGHT disrupt its normal activity OR (functioning).

What type of mutation is it?

How can gene mutations be passed down to future offspring?

• ONLY IF THEY OCCUR IN THE SEX CELLS

What are some characteristics of gene mutations?

• They can be dominant or recessive• They can occur on autosomal chromosomes

(pairs 1-22) or sex chromosomes (pair 23)• People that are heterozygous for a recessive

genetic disorder are called carriers• Carriers have one normal allele and one

diseased allele; They do not show symptoms for the disease but may pass the allele to future offspring

COLORBLINDNESS:A SEX-LINKED

DISORDER

Genetic Diseases caused by gene mutations:

Cystic FibrosisFaulty gene produces a defective protein that does not allow for the properremoval of mucous lining the cells of the lung and GItract.

Gene Mutations:

Faulty gene produces a defective enzymewhich cannot help remove fat from nerve cells.

Tay-Sachs Disease

Sickle-Cell Anemia:

One base is substituted for another and this causes the production of a distorted hemoglobin molecule (protein) which cannot function properly.

What do these three gene mutations have in common?

They all affect the shape of proteins!! If we changethe shape of proteins (enzymes) they will not function properly and this will affect our phenotype.

How do we trace/identify gene mutations in a population or family?

• Pedigree Charts: - A diagram that shows the presence or absence of a particular trait through each generation.

• Genetic Testing: Ability to diagnose vulnerabilities to various genetic disorders

Recessive Gene Pedigree Chart

cc

Cc Cc

A – Dominant Allele; a - Recessive

aa

aa

aa

aa

aa

AaAaAa

Aa Aa

?

?

H – Dominant Allele; h - Recessive

Hh

Hh Hh

Hh

hh

hh hh hh hh

hh hh hh hh hh

What is a chromosomal mutation?

• Any change in the number or structure of chromosomes

Chromosome Damage:

Part of a chromosome isrepeated.

Part of a chromosome is missing.

Reversing a fragment of thechromosome.

A fragment of one chromosome attaches to a nonhomlogous chromosome.

Abnormal Numbers of Chromosomes

• Polyploidy: Having many sets of chromosomes – 1.5n, 3n, 4n, 5n

Abnormal Numbers of Chromosomes

• Aneuploidy: The addition or loss of a whole chromosome

How do these mutations occur?

• NONDISJUNCTION: occurs when homologous chromosomes or sister chromatids fail to

separate during meiosis.

Normal Karyotype

Trisomy 21 – Down Syndrome

Trisomy 18 – Edward’s Syndrome

Monosomy X – Turner Syndrome

Chrom. #5 deletion: Cri-du-Chat Syndrome

Klinefelter’s Syndrome