Lecture 5 Flashcards
Point Mutations
Alteration of single base pair of DNA
Types of point mutations
Substitutions
Insertion or Deletion (INDEL)
Types of substitution mutations
Transition
Transversion
Transition
Changing a purine to a purine
or pyramidine to pyramidine
Transversion
Changing a purine to a pyrimidine
Or a pyrimidine to a purine
Classification for substitutions in protein coding DNA
Synonymous
Conseravtive missense
Nonconservative missense
Nonsense
Synonymous mutation
affects a codon in a position that does not alter the encoded amino acid
Missense mutation (conservative)
affects a codon so that a different amino acid is incorporated, but the “new” amino acid has similar properties as the “old” one
Missense mutation (nonconservative)
affects a codon so that a different amino acid is incorporated, but the “new” amino acid has different properties than the “old” one
Nonsense mutation (aka stop mutation)
changes a codon into a stop codon, causes premature termination (truncation) of the protein
Classification for INDELS in protein coding DNA
Frameshift mutation
Frameshift mutation
Since the reading frame is read in units of three nucleotides, a single base pair insertion or deletion within the reading frame will alter all codons from this point on until a stop codon is encountered.
Classification for INDELS and substitutions anywhere in the gene
Silent mutation
Silent mutation
mutations have no effect on the function of encoded protein/RNA, regardless of which part of the gene is hit.
Codon
Nucleotide triplets
T/F the genetic code is based on nucleotide quartets
False
Nucleotide triplets
Degenerate code
64 codons encode 20 amino acids and three termination signals
Wobble
Third position of codon is variable for 18 amino acids
In the third position of the codon, which would be less dramatic: transition or transversion?
transition
T/F point mutations in non coding dna are not harmful
False
Give examples of human disorders caused by point mutations
Cystic fibrosis
Preaxial polydactyly
SNPs
single nucleotide variations in the genome, which originated from point mutations and became “fixed” in the population
common” SNPs
occur > 5% in a population
Rare “SNPs”
< 5% in a population
Somatic mutations
Mutations in body cells
Genetic mosaic
contains somatic regions that are genotypically different from each other
Germline mutations
Occurs in gametes
Individual may or may not be affected
Offspring may or may not be affected
Pigmentation
Somatic mutation in embryonic cell gives rise to affected patch of tissue
Size of affected area depends on how early in development the mutation occured
Cancer
Mutations occur in adult cells
Cancers may be caused by somatic and/or germline mutations
chromosome mutations
changes in a region of DNA that harbors multiple genes
What are the three types of chromosome mutations
Gain
Lose
Relocate
Relocation chromosome mutations
Translocation
Inversion
Translocation chromosome mutations
A peice of gene from another chomosome replaces a gene
Inversion chromosome mutations
Two genes on the same chomosome switch places
Loss chromosome mutations
Deletion
Missing chomosome
Gain chromosome mutations
Duplication
Extra chomosome
Duplication chromosome mutations
A gene is duplicated
Ploidy
Number of chromosome sets in the cell. Equivalent to the “n” value
Polyploidy
Organisms with more than two chromosome sets (n>=3)
Euploidy
Refers to individual with any number of complete chromosome sets
Aneuploidy
Involves a change (gain or loss) of a whole single chromosome (of the set) and usually produces physical defects (despite all genes being normal). Example: trisomic (3) and monosomic (1) chromosomes
Monoploidy
Refers to a haploid individual member of a normally diploid species (e.g. male bees and wasps)
Allopolyploidy
A hybrid plant species that is derived from two or more species, containing two or more copies of each original genome (e.g. Brassica)
Autopolyploidy
Extra sets of chromosomes derived from the same species, caused by accidents in mitosis or meiosis
T/F rutabega is a hybrid
True
Hybrid of turnip and something else
What is the ploidy of seedless plants?
Triploid
T/F watermelon and bananas are seedless and triploid
True
T/F odd numbered ploidy is associated with sterility
True
How are sterile plants propagated
cuttings can be grown asexually
Tetraploid plant can be crossed to diploid plant to create triploid seeds
What is the problem with the cavendish banana?
It’s triploid and sterile, must be propogated asexually
Fungi can infect banana trees
These fungi;’s resistence is increasing
Cavendish bananas face threat of eradication
autosomes
Non sex chromosomes
Nondisjunction
Nondisjunction of one chromosome pair in meiosis results in gametes having either gained or lost a chromosome
T/F nondisjunction always happens at the second division of meiosis
False
Can occur at either one
What is the n value of the 4 daughter cells if nondisjunction occurs at the first div
n + 1
n + 1
n - 1
n - 1
What is the n value of the 4 daughter cells if nondisjunction occurs at the second div
n + 1
n - 1
n
n
What type of ploidy is downs syndrome
Aneuploidy
T/F most aneuploidies are fatal
True
karyogram
A visual depiction of all (metaphase) chromosomes in an organism
What is the most common form of downs syndrome
Trisomy 21
Fertility of people with downs syndrome
Females may be fertile males usually not
Turner Syndrome
XO Monosomy of X-chromosome Sterile females short stature, ovaries don't develop, webbed neck normal IQ
Klinefelter Syndrome
XXY
variable male genital development (hypogonadism)
May develop breasts after puberty
most/some show intellectual disability
Extra Y-chromosome
XYY
Individuals show marginal differences from normality.
not “criminal behavior”
Male, taller (+3”), but normal, fertile (gametes are either X or Y, never XY or YY)
Triple-X
XXX
can pass for normal, need karyotype to tell
most are fertile and produce normal children
increased stature
karyogram shorthand format
pos 1: tot. num. of chroms.
pos 2: sex chroms
pos 3: abnormalities
