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Transcript
Mutations
chapters
8 and 12
What Are Mutations?
• Changes in the
nucleotide sequence of
DNA
• May occur in somatic
cells (aren’t passed to
offspring)
• May occur in gametes
(eggs & sperm) and be
passed to offspring
Types of Mutations
Chromosome Mutations
• May Involve:
– Changing the
structure of a
chromosome
– The loss or
gain of part of
a chromosome
CROSSING OVER
when the DNA from one chromosome
becomes attached to another chromosome
- usually this occurs on
HOMOLOGOUS CHROMOSOMES during
PROPHASE I of MEIOSIS
GENETIC RECOMBINATION- change in the
genes or at least the location of genes
Chromosome Mutations
• Five types exist:
– Deletion
– Inversion
– Translocation
– Nondisjunction
– Duplication
Deletion
• Due to breakage
• A piece of a
chromosome is lost
Inversion
• Chromosome segment
breaks off
• Segment flips around
backwards
• Segment reattaches
Duplication
• Occurs when a
gene sequence is
repeated
Translocation
• Involves two
chromosomes that
aren’t homologous
• Part of one
chromosome is
transferred to
another chromosomes
Translocation
Nondisjunction
• Failure of chromosomes to
separate during meiosis
• Causes gamete to have too many
or too few chromosomes
• Disorders:
– Down Syndrome – three 21st
chromosomes
– Turner Syndrome – single X chromosome
– Klinefelter’s Syndrome – XXY
chromosomes
LAW OF INDEPENDENT
ASSORTMENT
•
during meiosis I- one
homologous
chromosome travels to
each cell. The
chromosomes are
chosen at random but the
odds you get all 23 from
the same parent is
unlikely.
Chromosome Mutation
Animation
Gene Mutations
• Change in the
nucleotide sequence
of a gene
• May only involve a
single nucleotide
• May be due to
copying errors,
chemicals, viruses,
etc.
Types of Gene Mutations
• Include:
– Point Mutations
– Substitutions
– Insertions
– Deletions
– Frameshift
Point Mutation
• Change of a single
nucleotide
• Includes the
deletion, insertion, or
substitution of ONE
nucleotide in a gene
Point Mutation
• Sickle Cell
disease is the
result of one
nucleotide
substitution
• Occurs in the
hemoglobin gene
Frameshift Mutation
• Inserting or deleting
one or more
nucleotides
• Changes the “reading
frame” like changing a
sentence
• Proteins built
incorrectly
Frameshift Mutation
• Original:
– The fat cat ate the wee
rat.
• Frame Shift (“a” added):
– The fat caa tet hew
eer at.
Amino Acid Sequence
Changed
Gene Mutation
Animation
FYI
Normal Male
2n = 46 26
Normal Female
2n = 46 27
Male, Trisomy 21 (Down’s)
2n = 47 28
Female Down’s Syndrome
2n = 47 29
Klinefelter’s Syndrome
2n = 47 30
Turner’s Syndrome
2n = 45
31