types of mutations. chromosome mutations may involve: –changing the structure of a chromosome...
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Types of Types of MutatioMutatio
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Chromosome Mutations
• May Involve:– Changing the
structure of a chromosome
– The loss or gain of part of a chromosome
– Ultimately they change either a gene or gene dosage
Chromosome Mutations
• Five types exist:–Deletion– Inversion–Translocation–Nondisjunction
–Duplication
Deletion
• Due to breakage• A piece of a
chromosome is lost
Angelman Syndrome• Caused by small
deletion on Ch 15 inherited from mom
• Paternal genes are normally suppressed
• Developmental delay• Happy and excitable• Hand flapping
Inversion
• Chromosome segment breaks off
• Segment flips around backwards
• Segment reattaches
• Usually do not lead to abnormalities
• Lead to decreased fertility
Consequences of Inversions
Duplication
• Occurs when a gene sequence is repeated
Charcot-Marie-Tooth Syndrome• Chr 17 duplication• Inherited• Weakness of foot
and lower leg muscles
• High arches, hammertoes, and other deformities
Translocation
• Involves two chromosomes that aren’t homologous
•Part of one chromosome is transferred to another chromosomes
Philadelphia Translocation
• Individuals develop leukemia
• Part of 8 and 22 go to Ch 9.
• Fusion event leads to misexpression of one gene
• Not inherited!
Philadelphia Chromosome
Translocation
Nondisjunction
•Failure of chromosomes to separate during meiosis
• Causes gamete to have too many or too few chromosomes
Symptoms of Klinefelter Syndrome (XXY)
• breast enlargement
• lack of facial and body hair
• likelihood to be overweight and taller than average males
• Infertile (no sperm)
Chromosome Mutation Animation
Gene Mutations
• Change in the nucleotide sequence of a gene
• May only involve a single nucleotide
• May be due to copying errors, chemicals, viruses, etc.
Point Mutation
• Change of a single nucleotide
• Includes the deletion, insertion, or substitution of ONE nucleotide in a gene
Point Mutation
•Sickle Cell disease is the result of one nucleotide substitution
• Occurs in the hemoglobin gene
Sickle Cell Disease Results from a Base Change in Beta Globin Gene
Figure 12.1
Frameshift Mutation
• Inserting or deleting one or more nucleotides
• Changes the “reading frame” like changing a sentence
•Proteins built incorrectly
Frameshift Mutation
• Original:–The fat cat ate the wee rat.
• Frame Shift (“a” added):– The fat caa tet hew eer at.
Amino Acid Sequence Changed
Gene Mutation Animation
Pedigree Analysis–figure out the
genetic basis of a disease or trait from its inheritance pattern
–predict the risk of disease in future offspring in a family (genetic counseling)
Basic patterns of inheritance
– autosomal, recessive– autosomal, dominant– X-linked, recessive– X-linked, dominant
(very rare)
• Trait is rare in pedigree
• Trait often skips generations (hidden in heterozygous carriers)
• Trait affects males and females equally
Autosomal recessive traits
Autosomal Recessive mutations
Autosomal Dominant
• Trait is common in the pedigree
• Trait is found in every generation
• Affected individuals transmit the trait to ~1/2 of their children (regardless of sex)
Autosomal Dominant
X-linked recessive
• Trait is rare in pedigree
• Trait skips generations
• Affected fathers DO NOT pass to their sons,
• Males are more often affected than females
X-linked recessive
Pedigree Analysis in real life
Remember: •dominant traits may be rare in population
• recessive traits may be common in population
• alleles may come into the pedigree from 2 sources
• mutation happens
• often traits are more complex
• affected by environment & other genes
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