6.1.2 Types of Mutations Flashcards
Gene/Point Mutations
Types of Mutations
Alterations to one or a few bases by substitution, addition or deletion from a DNA strand at a single point.
Base Substitution
Point Mutation
Can cause three forms of mutation:
- Silent - different mRNA codon but no change to the amino acid sequence
- Missense - a change to one amino acid in the sequence
- Nonsense - a premature stop codon shortens the entire chain, resulting in a non-functional protein
Base Insertions and Deletions
Point Mutation
Can cause a frameshift mutation by shifting the reading frame of each codon, usually resulting in a non-functional protein.
Chromosomal Mutations
Types of Mutations
Can be caused by environmental or natural factors that cause chromosomes to break and not rejoin in the same pattern, damaging the structure. Alternatively, the number of chromosomes can change.
Deletion
Structural Chromosomal Mutation
One or more genes are removed when the end of a chromosome breaks off or when two simultaneous breaks lead to the loss of a segment
Duplication
Structural Chromosomal Mutation
The copying of a chromosomal segment, resulting in a repeating section in the chromosome
Inversion
Structural Chromosomal Mutation
A segment is separated from the chromosome and reinserts in the reverse order
Translocation
Structural Chromosomal Mutation
A segment is removed from one chromosome and inserts on another
Aneuploidy
Chromosomal Mutations
A change in the chromosome number, which occurs when there are copies of or missing chromosomes. This often involves nondisjunction, where chromosomes fail to separate during meiosis for gametes, which will result in an offspring with a missing or extra chromosome.
Karyotype
Chromosomal Mutations
- A photograph of all an organism’s chromosomes, allowing doctors to observe abnormalities and their resulting conditions
- Can be used by doctors to diagnose and treat genetic disorders in comparison to the standard human karyotype, where they will compare the total number and the pairings.
Down Syndrome
Non-Disjunction Conditions
Also known as trisomy-21, as it is a result of having three copies of chromosome 21 due to nondisjunction.
It results in characteristic features such as short stature, broad hands, wide faces and a large protruding tongue.
The odds of developing Down Syndrome are 1/750.
Klinefelter’s Syndrome
Nondisjunction Conditions
A chromosome makeup of XXY results in sterility, tall stature, small testicles, developed breasts and mental deficiency.
The odds of developing Klinefelter’s syndrome are 1/1000 males.
Turner’s Syndrome
Nondisjunction Conditions
A chromosome makeup of X only results in a female that will not undergo puberty, meaning no menstruation, breast development or fertility.
The odds of developing Turner’s Syndrome are 1/2500 females
Edward’s Syndrome
Nondisjunction Conditions
An extra number 18 chromosome results in physical symptoms such as:
- Low ears
- Kidney and heart defects
- Prominent back part of skull
- Prominent heels
- Shield chest
- Small jaw
The odds of developing Edward’s syndrome are 1/5000.
Patau’s Syndrome
Nondisjunction Conditions
An extra number 13 chromosome (trisomy 13) results in physical symptoms of a broad nose, polydactyly, a small cranium, deformed eyes and possibly hear defects and mental retardation.
The odds of developing Patau’s syndrome are 1/15000.
Jacob’s Syndrome
Nondisjunction Conditions
A chromosome makeup of XYY results in abnormal tallness, heavy cases of acne and low mental ability.
The odds of developing Jacob’s syndrome are 1/1000 males.
Triple X
Nondisjunction Conditions
A chromosome makeup of XXX is associated with no specific abnormalities but may have underdeveloped genitalia and limited fertility.
The odds of developing Triple X are 1/1000 females.
Cri-Du-Chat
Nondisjunction Conditions
Also known as “cry of the cat” syndrome, a deletion of about half of the short arm of chromosome 5 results in severe mental retardation, a small cranium, a small jaw, a moon shaped face and an undeveloped larynx.
The odds of developing cri-du-chat are 1/100,000.
Effects of Mutations
Dependent on the location of mutation:
- Protein-Coding Gene - alters the protein produced
- Regulatory Region - increased or decreased production of a protein
- Gamete - germ-line mutation can be inherited by the offspring
- Somatic Cells - somatic mutationare often harmless but can impact cell division or cause uncontrolled cell replication (cancer)
Sickle Cell Anemia
Single-Gene Mutation Case Studies
A base substitution causes the normal allele (H^N) to become H^S.
The sickle shape of the cells means poor oxygen transport.
However, those with the gene are less liekly to catch malaria as the malaria parasite dies inside of sickle cells
Haemochromatosis
Single-Gene Mutation Case Studies
A base substition of thymine instead of cytosine in codon 282 of chromosome 6 creates an impaired HFE protein, which is usually required to regulate iron absorption and iron levels in the body.
Incorrect regulation of iron in body tissues results in levels 5-10 times higher than normal, which can have a particular impact on the liver, brain and heart.
This could lead to fatigue, liver damage, arthritis, diabetes and/or heart failure.
Double-Muscled Cattle
Single-Gene Mutation Case Studies
A base deletion results in a frameshift in the myostatin gene and a premature stop codon, making it a non-functional protein.
Mysostatin protein regulates muscle cell growth, so the mutation causes excessive muscle growth.
The Belgian Blue cattle produce higher muscle mass than other breeds and higher qualities of lean meat.
Cystic Fibrosis in Humans
Single-Gene Mutation Case Studies
There are over 3000 different mutations that can occur in the CFTR gene, which generally cause the CFTR protein to be unable to fold correctly and then break down.
These cause cystic fibrosis, a life threatening disease but can also create a resistance to typhoid fever.
