Download Mutations

Mutations
When something goes wrong…
Causes of Mutations
• Mutations are caused by changes in the
nucleotide sequence of DNA (A, T, C, G) or of
a gene (specific area of a chromosome)
• This can occur:
– During DNA replication
– During cell division
– After cell division
Mutations Types
• Germ-Cell Mutations
– Occur in an organism’s sex cells
– Do not affect the organism itself but may be
passed to offspring
• Somatic-Cell Mutations
– Take place in an organisms body cells and can
affect the organism
– Cannot be inherited
• Lethal Mutations
– Cause death, often before birth
Gene Mutations
Gene Mutations
• Point mutations affect a single nucleotide
• Base pair substitutions switches a nucleotide
– Silent mutation
• Does not change the amino acid
– Missence mutation
• Change of a single amino acid
– Nonsense mutation
• Changes amino acid to stop codon
– Neutral mutation
• Changes amino acid to chemical similar amino acid
Gene Mutations
• Frameshift Mutation
– Change in reading frame due to adding or
deleting a nucleotide
AAT TGC CCG ACT TTT CGC CAT
• Add A after 2nd nucleotide
AAA TTG CCC GAC TTT TCG CCA T
Chromosomal
Mutations
Chromosomal Mutations
• These mutations can be detected by karyotyping
– Nondisjunction
• Homologous chromosomes or chromatids don’t split in division
– Deletion
• Loss of a piece of chromosome due to breakage
– Duplication
• Portion of the chromosome can be duplicated
– Inversion
• Part breaks off, then reattaches in reverse position
– Translocation
• Part breaks off, reattaches to a non-homologous chromosomes
– Insertion
• Extra DNA is inserted into a non-homologous chromosome
Effects of Mutations
• Always result in changes to genotype (DNA)
but not always phenotype (what you see!)
– Neutral
• No effect
– Beneficial
• Enhances fitness
– Deleterious
• Decreases fitness
Cystic Fibrosis
Cystic Fibrosis
• Genetic disorder affecting the respiratory and
digestive system caused by defective gene on
Chromosome 7
– 1000 different mutations in this gene have been identified
– Most often caused by deletion of a single amino acid
• Body produces a mucous that clogs the airways and
increases risks of infection
• Both parents must pass on the gene to their children
– More than 10 million Americans carry the gene and don’t
know it
• About 2,500 babies are born with cystic fibrosis in
the U.S. each year.
Turner Syndrome
Turner Syndrome
• Caused by missing or incomplete X chromosome
often due to non-disjunction
• Women with Turner syndrome are usually sterile
and cannot have children
• Short in stature, stocky appearance, arms that turn
out slightly at the elbow, receding jaw line, short
webbed neck, and low hairline
• Affects 60,000 females in the United States. This
disorder is seen in 1 of every 2000 to 2500 babies
born, with about 800 new cases diagnosed each year
• In 75-80% of cases, the single X chromosome comes
from the mother's egg; the father's sperm that
fertilizes the egg is missing its sex chromosome
Klinefelter Syndrome
Klinefelter Syndrome
• Caused by an extra X chromosome (XXY) in males
due to by nondisjuction
• Males are often tall and don’t develop secondary sex
characteristics (facial hair, underarm hair, etc)
• Often not diagnosed until puberty (less muscular
body, more breast tissue, less hair) or when men try
to have children due to sterility
• Treated with hormone replacement therapy –
testosterone injections
• Klinefelter syndrome is one of the most common
genetic abnormalities. It affects between 1 in 500 and
1 in 1,000 males.
Sickle Cell Disease
Sickle Cell Disease
• Mutation on a gene on chromosome 11 that codes for the
shape
• Blood cells get stuck in the blood vessels and cannot
transport oxygen, resulting in pain and damage to
organs, leading to low red blood cell counts
• Both parents must pas a defective gene to their children
• Daily penicillin to prevent infections, folic acid to build
new cells, blood transfusions, bone marrow transplant
• Unlike normal red blood cells, which can live for 120
days, sickle-shaped cells live only 10 to 20 days.
• In the United States, the disease most commonly affects
African-Americans. About 1 out of every 500 AfricanAmerican babies born in the United States has sickle cell
anemia