Chapter 14 Sec 1: Genes in Action

Mutation: The Basis of Genetic Change

• The change in the structure or amount of the genetic material of an organism

Mutant

• An individual whose DNA or chromosomes differ from a previous or normal state.

Evolution

• Genetic differences among organisms originate as some kind of genetic mutation

Causes of Mutation• Occur naturally as accidental changes to DNA

or to chromosomes during the cell cycle– Mutagens: environmental factors like radiation &

some chemicals

Effects of Mutation

• A small change in the DNA can affect one amino acid in a protein– Only noticed if they cause a disease

Kinds of Mutations

• Different kinds of mutations are recognized as either changes in DNA or changes in the results of genes

Mutations as Changes in DNA

Point Mutation

• Change of a single nucleotide in a sequence from one kind of base to another

Insertion or Deletion

• Errors in replication can cause the deletion or insertion of a nucleotide

Mutations as Changes in Results of Genes

Silent Mutation

• It has no effect on a gene’s function– Point mutation

Missense Mutation

• Results when a codon is changed such that the new codon codes for a different amino acid

Frameshift Mutation

• Causes the starting point of “reading” the gene to change which translates to different codons

Nonsense Mutation

• Results when a codon is changed to a STOP signal– Protein may fail to function

More or Fewer Amino Acids

• If the insertion or deletion is a multiple of 3, reading will be preserved

• Protein will have fewer amino acids

Chromosomal Mutations

At a chromosome level• In eukaryotic cells, the process of meiosis

creates the chance of mutations at the chromosome level

Deletion

• Occurs when a piece of chromosome is lost

Duplication

• Occurs when a piece remains attached to its homologous chromosome after meiosis

Inversion

• Occurs when a piece reattaches to its original chromosome, but in a reverse direction

Translocation

• Occurs when a chromosome piece ends up in a completely different, nonhomologous chromosome

Gene Rearrangement

• Chromosomal mutation can move an entire gene to a new location

• Likely to disrupt the gene’s function

Effects of Genetic Change

Germ Cell

• Mutations in germ cells can be passed on to the next generation

Sickle Cell Anemia

• Recessive trait• Poor blood circulation, pain, organ damage

Tay-Sachs Disease

• Recessive trait• Deterioration of central nervous system• Death in early childhood• Caused by defective form of an enzyme

Cystic Fibrosis

• Recessive trait• Mucus buildup in

organs• Difficulty breathing and

digesting

Hemophilia

• Recessive, sex linked• Failure of blood to clot, excessive bleeding

and bruising

Romanoffs - Hemophilia

Pedigree for Hemophilia

Huntington Disease

• Dominant trait• Gradual deterioration of brain tissue in middle

age• Shorter life expectancy

Achondroplasia

• Homozygous Dominant – Don’t survive

• Heterozygous Dominant – Lead normal lives and can reproduce

Camptodactyly

• Genetic abnormality that affects the shape and movement of fingers

• Variation in the phenotype of the trait

Examples:

Cri-du-chat

• Deletion from chromosome 5 resulting in mental retardation and the development of an abnormally shaped larynx

Progeria Syndrome

• A set of symptoms that characterize a disorder– Hutchinson-Gilford Progeria syndrome: mutated

gene that leads to premature aging and reduced life expectancy

Progeria Syndrome

• Gene mutates at random• Dominant over

its normal partner on the homologous chromosome

Progeria Syndrome

Large-scale genetic change

• Can occur by misplacement, recombination, or multiplication of entire chromosomes

Nondisjunction

• When pairs of chromosomes fail to separate properly

Down Syndrome

• Extra chromosome 21• Mental retardation• Congenital heart defects• Shorter limbs

Karyotype

Turner Syndrome (XO)• Missing one X chromosome• Female in appearance but their sex organs do

not develop at puberty and they are sterile• Short stature, broad based neck

Turner Syndrome

Klinefelters Syndrome (XXY)

• Male in appearance and sterile• Taller than average• Usually notice when

males don’t develop at puberty

Karyotype

XYY

• Individuals are somewhat taller than average and often have below normal intelligence

• Used to think they were prone to violence