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MUTATIONS (CHROMOSOMAL MUTATION (change in structure (translocation…
MUTATIONS
CHROMOSOMAL MUTATION
change in structure or number of chromosome
change in structure
occurs during prophase I of meiosis (crossing over)
translocation
portion detaches and rejoins (same or another chromosome) at a different point
duplication
portion of chromosome replicated
duplication of gene - increased expression
inversion
segments between 2 breakpoints flips and reinserts in same chromosome
deletion
loss of portion of chromosome
change in number
due to issues in chromosome segregation during anaphase
aneuploidy
extra or missing chromosome
due to non-disjunction during anaphase
polyploidy
more than 2 sets of chromosomes
EFFECTS
Down syndrome
failure of separation of homologous chromosome 21 during anaphase 1 of meiosis I
aneuploidy - gamete with extra copy of chromosome 21
zygote has (2n+1) chromosomes
characteristics
mental retardation
lower lifespan
sexually underdeveloped and sterile
facial features, short stature
sickle cell anaemia
single base substitution of A to U (in mRNA) - T to A in template
GAG (glutamic acid) replaced by GUG (valine)
valine hydrophobic while glutamic acid is hydrophilic
Hbs in haemoglobin chain instead of Hbs
in low oxygen, Hbs molecules precipitate out of solution to form rigid fibres
red blood cells become sickle shaped
GENE MUTATION
change in nucleotide base sequence
error transmitted to mRNA during transcription
different amino acid sequence - different polypeptide
change in tertiary arrangement of protein (interactions)
loss in function of protein
gain in function of protein
types
insertions
frame-shift mutation
reading frame of mRNA after insertion.deletion changed
deletions
substitutions
may transfer original codon to stop codon
premature termination of translation --> truncated protein
nonsense mutation
insignificant change
new amino acid may have similar properties
conformation of polypeptide (and functionality of protein) remains
missense mutation
no change
codon codes for same amino acid
due to degeneracy of genetic code