Chapter 8
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Part 1: Genes, Chromosomes, and Heredity
Chromosome Mutations
Review
Variations in chromosome
number
can arise from
, in which chromosomes or chromatids fail to
disjoin
during
.
for anything other than the
chromosome
is often fatal. In
monosomy,
such as
syndrome,
only a section of a chromosome is lost.
usually exhibits less severe effects than monosomy; many plants can be viable in this
state.
A trisomic cell shows irregular pairing during
: the 3 chromosomes may
synapse
to form a
.
In humans, trisomy of chromosome
21
results in
syndrome,
usually caused by nondisjunction of the
chromosome
21 during meiosis.
Other examples of trisomy syndromes are
Patau
syndrome (trisomy
) and
Edwards
syndrome (trisomy
).
Polyploidy (more than 2 haploid sets of chromosomes) occurs mostly in plants, and can be
either
or
, and
sometimes
.
Amphidiploid plants can also be produced by
cell
hybridization.
Rearrangements of chromosome
segments
include
,
,
, and
.
A chromosome
(or a deficiency) can occur near one end (
deletion
) or from the interior of the chromosome (
deletion
).
A deletion in recessive mutants may
exhibit
in a heterozygote.
A
is a repeated segment of DNA caused by
crossing
over
during meiosis or through a replication error prior to meiosis.
A
duplicated
gene may exhibit phenotypic variations in genes that exhibit
An
involves a rearrangement of the linear gene
sequence
and may arise from chromosomal
; the inversion can be
paracentric
or
pericentri
.
is a movement of a chromosomal segment to a new location in the genome.
A
translocation
involves the exchange between
chromosomes; its unusual
synapsis
can also produce inviable gametes.
A common human rearrangement is
translocation.
Some chromosome sites are
and susceptible to breakage, causing disorders such as Fragile
syndrome,
which is the most common form of inherited mental retardation.
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Oct 16, 2008
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