Mutations Affecting Chromosome Structure
Normal Chromosomes (for comparison)
a
p
b
q
c
d
r
s
e
t
f
u
g
a
a
b
b
c
c
d
d
e
e
f
f
g
g
h
h
p
p
q
q
r
r
s
s
t
t
u
u
h
• Non-homologous chromosomes.
Genetics Handout 20.1
• Paired at metaphase 1.
• Lines represent both sister chromatids.
Mutations Affecting Chromosome Structure (continued)
Deletion (or Deficiency)
a
a
a b
d
d
d c
e
e
e
f
f
f
g
g
g
h
h
h
• Deletion of region b-c.
•
•
•
•
• Paired at metaphase 1.
• Lines represent both sister chromatids.
• Red is deletion chromosome, blue is
normal chromosome.
Most deletions are lethal when homozygous.
Large deletions may be lethal when heterozygous.
Heterozygotes are hemizygous for genes within the region deleted.
Heterozygotes have suppressed recombination within the region deleted.
Genetics Handout 20.2
Mutations Affecting Chromosome Structure (continued)
Duplication
a
b
a
a
c
b
b
d
c
c
d
d
e
g f
e
f g
h
g
e
f
g
f
g
f
h
h
• Duplication of region f-g.
• Paired at metaphase 1.
• Lines represent both sister chromatids.
• Red is duplication chromosome, blue is
normal chromosome.
• Large duplications may be lethal when homozygous or heterozygous.
• Small duplications are often difficult to detect genetically.
Genetics Handout 20.3
Mutations Affecting Chromosome Structure (continued)
Paracentric Inversion
a
a
c
a
b
c
b
d
d
d
e
e
e
f
f
f
g
g
g
h
h
b
c
h
• Inversion of region b-c.
a
a
b
c
b
c
• Paired at metaphase 1.
• Lines represent both sister chromatids.
• Red is inversion chromosome, blue is
normal chromosome.
a
c b
a
d
d
e
e
e
e
f
f
f
f
g
g
g
g
h
h
h
h
• Crossover within inversion loop.
• Lines represent only chromatids involved
in crossover. Non-crossover chromatids
are not shown.
d
b c
d
• Crossover chromatids generate acentric
fragment and dicentric bridge. Neither
will form functional gametes.
• Non-crossover chromatids (not shown;
one inversion, one normal) will generate
functional gametes.
• Recombination within inversion is
suppressed.
• Linkage map is altered when homozygous.
• Heterozygotes have suppressed recombination within the region inverted.
Genetics Handout 20.4
Mutations Affecting Chromosome Structure (continued)
Pericentric Inversion
a
a
b
b
e
a
b
c
d
c
d
e
d
c
f
e
f
f
g
g
g
h
h
h
• Inversion of region c-e.
• Paired at metaphase 1.
• Lines represent both sister chromatids.
• Red is inversion chromosome, blue is
normal chromosome.
h
a
b
a
b
c
c
d
d
a
g
b
f
e
e
d
d
c
c
b
f
a
g
e
f
e
f
g
g
h
h
h
• Crossover within inversion loop.
• Lines represent only chromatids involved
in crossover. Non-crossover chromatids
are not shown.
• Crossover chromatids generate large
deletions and duplications. Neither will
form functional gametes.
• Non-crossover chromatids (not shown;
one inversion, one normal) will generate
functional gametes.
• Recombination within inversion is
suppressed.
• Linkage map is altered when homozygous.
• Heterozygotes have suppressed recombination within the region inverted.
Genetics Handout 20.5
Mutations Affecting Chromosome Structure (continued)
Reciprocal (or Balanced) Translocation
a
a
a
p
b
b
b
q
c
c
d
d
e
e
f
f
r
r
q
q
p
p
c
d
r
g
e
h
h g
s t u
f
s
h g
s t u
t
u
• Reciprocal translocation of region g-h
and region s-u.
•
•
•
•
• Paired at metaphase 1.
• Lines represent both sister chromatids.
• Red and yellow are reciprocal
translocation chromosomes, blue and
green are normal chromosomes.
• Segregation of adjacent (left and right or
top and bottom) chromosomes generates
large deletions and duplications and will
not produce functional gametes.
• Segregation of alternate chromosomes
(top left with bottom right (both normal)
and top right with bottom left (both
translocated)) will produce functional
gametes.
Linkage groups are altered when homozygous.
Linkage maps are complex when heterozygous.
Heterozygotes have reduced fertility.
Position effect can alter expression of translocated genes.
Genetics Handout 20.6
Mutations Affecting Chromosome Number
Normal Euploidy (for comparison)
• Diploid (2n, n = 4)
• Ploidy values other than two are normal in some species.
Alloploidy
• Allotetraploid (2(n1 + n2))
• Chromosome sets are from different,
but closely related, ancestral species
• Normal in many plants.
• Odd ploidy values are sterile. Even ploidy values are fertile.
• Plants with odd ploidy values can reproduce asexually.
Abnormal Euploidy
• Triploid (3n)
• Odd ploidy values are sterile. Even ploidy values can be fertile.
• Plants with odd ploidy values can reproduce asexually.
Genetics Handout 20.7
Mutations Affecting Chromosome Number (continued)
Aneuploidy
• Nullisomic (2n – 2)
• Lethal, except in some alloploid plants
• Monosomic (2n – 1)
• Hemizygous for genes on affected
chromosome
• Trisomic (2n + 1)
Genetics Handout 20.8