Mutations Flashcards
Define mutation
A change in genetic information (DNA )
T or F: mutations are responsible for the huge diversity of genes and are a source of new genes
True
What are the two scales of mutations?
Large scale
Small scale
What is a genetic disorder or hereditary disease?
when a mutation has an adverse effect on the phenotype
Define forward mutation
A change from the wild type allele to a different allele
Define wild type
The phenotype most commonly observed in natural populations
Define reverse (reversion) mutation
A change from the mutant allele to the wild type allele
Define germ-line mutation
Mutation that can affect future generations because they occur in the gametes
Define somatic mutation
Mutation that only affects individuals, often causes cancer
What are two causes of mutations?
- induced
- caused by mutagens - Spontaneous:
- errors during replication
Define mutagens and provide examples
physical and chemical agents that interact with DNA and cause mutations
ex. UV and X rays (physical)
or nucleotide analogs that are chemically similar to DNA nucleotides but pair incorrectly (chemical)
Define small-scale mutations and list the 3 types
Change in one or a few nucleotide pairs
- silent mutations
- missense mutations
- nonsense mutations
Define silent mutations and phenotypic results
Small-scale mutations that occur from a change in a nucleotide pair that does not change which amino acid the codon is translated to
No observable effect on phenotype because the same amino acid is coded for
Which letter in the codon triplet would have the least effect if changed?
The third one
Define missense mutations and phenotypic results
Small scale mutation that changes one amino acid to another
May have a little effect on the protein if:
- the amino acids have similar properties
- if the amino acid is in a region of the protein where the function of the protein wouldn’t be affected
or it can have a phenotypic effect if not.
Define nonsense mutations and phenotypic results
Small scale mutation where the codon is changed from coding for an amino acid into a stop codon
causes translation to be terminated before the polypeptide is complete
Usually leads to nonfunctional proteins
Define point mutations and list the two main types
Changes in a single nucleotide pair, occurs in small scale mutations
- substitution
- indel
When will a point mutation be inherited by offspring? What is an example of this?
If it occurs in a gamete or pre-gametic cell
ex. familial cardiomyopathy
Define substitution mutations and describe the mutation result that can occur
A point mutation that replaces one base pair with another
usually causes missense mutations
some can be silent due to the redundancy of genetic code
some can be nonsense
What is an example of a substitution missense mutation?
Sickle-cell anemia
Results in an abnormal beta-globin polypeptide
Define indel mutations and list the two kinds
A point mutation that is caused by the insertion or deletion of one or more nucleotide pairs
- insertion: addition of a nucleotide pair in a gene
- deletion: loss of a nucleotide pair in a gene
What are the consequences of indel mutations?
Usually severe because they can cause a frameshift mutation
Can cause extensive missense that usually ends in nonsense
Define frameshift mutation
Changes to the reading frame in which the nucleotide triplets are read in different groups (and therefore code for different amino acids)
caused by indel point mutations
Define large scale mutations
Abnormal chromosome number or alterations of chromosome structure
Define genome mutations
Changes in chromosome number, either polyploidy or aneuploidy
Define euploidy
A genome mutation
an exact multiple of the haploid number of chromosomes
Define polyploidy
A genome mutation with more than two complete sets of chromosomes
Which type of large scale mutation is common in plants?
Polyploidy
Define monoploidy
A genome mutation that results in lethal alleles being expressed
Which animal species are monoploidy?
male bees, wasps and ants that develop from unfertilized eggs
Define triploid
3 complete sets of chromosomes
usually sterile
ex. watermelon and bananas
Define aneuploidy
Having an abnormal number of a particular chromosome
ex. 2n-1 or 2n+1 for a diploid organism
T or F: most human aneuploid embryos survive until birth
FALSE. mostly spontaneously abort
What can cause aneuploidy?
nondisjunction
Define nondisjunction
Failure of homologous chromosomes to separate during meiosis I
or
Failure of sister chromatids to separate during meiosis II
This can also happen to sister chromatids in mitosis
What are two aneuploidy results of nondisjunction?
Monosomy and trisomy
Describe monosomy. Which syndrome survives to birth?
An aneuploidy result of nondisjunction that results in only one chromosome of a pair (2n-1)
Turner Syndrome (XO) - only in females, short, usually infertile
Describe trisomy. Which syndromes survive to birth?
An aneuploidy result of nondisjunction which results in an extra copy of a chromosome (2n+1)
XXY (Klinefelter syndrome)
XYY syndrome
XXX
What is the only autosomal trisomy that can be survived into adulthood?
Trisomy 21 (Down’s Syndrome)
What causes chromosome mutation?
Errors in meiosis (chromosome breakage, improper crossing over) or damage from things like radiation
Why does chromosome mutation cause problems?
Because of an imbalance of genetic material or damage to genes at break sites
What are the four types of changes that can occur in chromosome structure?
Deletion
Duplication
Inversion
Translocation
Define deletion
A type of alteration to chromosome structure
Occurs when a chromosomal fragment is lost and the chromosome is then missing some genes
What are the consequences of deletion in chromosome structures?
On X chromosome of male, it is usually lethal
Cri du Chat (chromosome 5) has severe effects
Define duplication
A type of alteration to chromosome structure
A deleted fragment can become attached to a sister chromatid
What are the consequences of duplication in chromosome structures?
ex. duplication of potentially cancer causing genes can cause cancer
Define inversion
A type of alteration to chromosome structure
When a deleted fragment reattaches to the original chromosome but in the reverse orientation
What are the consequences of inversion in chromosome structures?
Most human inversion occurs on chromosome 9 and can impact fertility
Define translocation
A type of alteration to chromosome structure
When a deleted fragment joins a non-homologous chromosomes
What are the consequences of translocation in chromosome structures?
ex. if SRY gene from Y chromosome is moved to an X chromosome, it results in XX male syndrome
