Transcript Chapter 14: Genes in Action

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
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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
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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