DNA Mutations and Repairs Flashcards
Mutation
process by which the sequence of base pairs in a DNA molecule is altered
Somatic Mutation
mutation in somatic cells, only affects individual
Germ-line mutation
mutation in germ line, transmitted by gametes to the next generation
Base pair substitutions
one bp replaced by another
Base pair insertions or deletions
1+ bp are added or deleted
Transition
Bp substitution from purine to purine or one pyrimidine to pyrimidine
Transversion
Bp substitution from purine to pyrimidine or vice versa
Missense mutation
causes a change in codon and a different amino acid is inserted into the polypeptide
Nonsense mutation
change from codon that specifies an amino acid to a stop codon
Neutral mutation
change in codon so that a different aa is inserted but the aa substitution doesn’t change the protein function
Silent mutation
change in codon but same aa inserted
Frameshift mutation
Reading frame changes downstream of the mutation
incorrect aa are added
usually non-functional protein
Repair Mechanisms
Enzyme-based repair systems
1.Direct correction: reverses the damage
2. Excision of damaged area and new synthesis of DNA
can read intact info from undamaged strand of DNA
What are the 4 chromosomal mutations?
- Deletion
- Duplication
- Inversion
- Translocation
Deletion
part of the chromosome is missing
Duplication
doubling of a segment of the chromosome
Tandem Duplication
doubling of a segment of a chromosome that is close together
Displaced Duplication
doubling of a segment on a chromosome that is in different locations on the same or different chromosome
Inversion
a segment of a chromosome is cut and rotated 180 degrees and reinserted
PERIcentric inversion
includes centromere
PARAcentric
centromere not included
What is the difference between inversion on a homozygote vs inversion heterozygote?
Homozygote wont cause any meiotic problems
heterozygote crossing over can serious genetic effect
Translocation
change in position of chromosome segments and the genes they contain (involves nonhomologous chromosomes.
What are the consequences that can happen because of translocation?
Homozygotes- no effect
Heterozygotes- affects meiosis
gametes unbalanced (duplications and deletions)
some gametes inviable
some viable but produce deficient phenotype (down syndrome)
Aneuploidy
Changes in the # of individual chromosomes (2n-1
Aneuploidy
Changes in the # of individual chromosomes (2n-1,2n+1,2n+2)
Polyploidy
Changes the # of chromosome sets (2n,3n,4n)
How are Aneuploids formed?
- deletion including centromere
- nondisjunction of 1+ chromosomes during meiosis
Nondisjunction
failure of sister chromatids to move to opposite poles at anaphase.
one gamete ends up with an extra chromosome and the other missing one
Nullisomy
loss of one homologous chromosome (2n-2)
Monosomy
Loss of a single chromosome (2n-1)
Trisomy
addition of a single chromosome (2n+1)
tetrasomy
addition of an extra pair of chromosomes (2n+2)
Nullisomic
2n-2, a pair of chromosomes missing in a single slot
Monosomic
2n-1, a single chromosome missing from one slot
Doubly monosomic
2n-1-1, two single chromosomes missing from 2 slots
Trisomic
2n+1, and extra single chromosome in 1 slot
Tetrasomic
2n+2, two chromosome pairs added to 1 slot
Doubly tertasomic
2n+2+2, two chromosome pairs added to 2 slots
Monoploids
individuals with 1 complete set of chromosomes (n)
Diploids
Individuals with 2 complete sets of chromosomes (2n)
Polyploids
Individuals have 3+ complete sets of chromosomes (3n,4n,5n….)
Polypoid plants that are even means? odd?
Plants with even numbers are fertile
odd means plant will be sterile
Difference between sexual and asexual polyploidization?
Sexual: Produces gametes that are unreduced (parents 2n = gametes 2n = 4n polyploid zygote = 4n polyploid adult)
Asexual: doubles chromosomes through abortive mitotic division (parents 2n = gametes n = normal zygote 2n = 4n Polyploid adult)
Autopolyploid
chromosome sets from same species
Allopolyploid
multiple chromosome sets from different but related species (2n = 4x =48, 2n = 6x = 42…..)