chromosomal aberrations Flashcards
Aneuploidy
an organism gains or loses one or more chromosomes but not a complete set
Aneuploidy
- Monosomy (2n - 1) – l
Trisomy (2n + 1)
Aneuploidy
loses of a single chromosome from an otherwise diploid genome
Monosomy
– gain of one chromosome
trisomy (2n + 1
complete haploid sets of chromosomes are present
Euploidy
more than two sets are present, the term ___ applies
polyploidy
three sets of chromosomes
Triploid (3n)
four sets of chromosomes
Tetraploid
These chromosomal variation
originates as a random error
during the production of
gametes, a phenomenon
referred to as ___,
whereby paired homologs fail
to disjoin during segregation
nondisjunction
does it Can happen during meiosis I or
meiosis II?
yes
Most common cause is nondisjunction (especially during meiosis)
Aneuploidy
- The phenotypic effects range from minor physical symptoms to devastating
and lethal deficiencies in major organ systems
Aneuploidy
Among survivors, phenotypic effects often include behavioral deficits and
mental retardation
Aneuploidy
It is the loss of one chromosome from a diploid complement
Monosomy
Although monosomy for the X chromosome occurs in humans, monosomy for any of the
autosomes is not usually )___ in humans or animals
tolerated
the failure of monosomic individuals to survive is first quite puzzling, since at least a
single copy of every gene is present in the remaining homolog
Monosomy
An explanation is that if just one of those genes is represented by a ___monosomy unmasks the recessive lethal allele
lethal allele,
In other cases, a single copy of a recessive gene may be insufficient to provide life
sustaining function (called ___)
haploinsufficiency
Addition of an extra chromosome produces somewhat more viable
individuals than does the loss of a chromosome
true or false
true
In animals, this is often true, provided that the chromosome involved is
relatively small
Trisomy
- The addition of a large autosome to the diploid complement in humans has
sever effects and is usually lethal during development
Trisomy
Describes instances in which more than two multiples of the haploid chromosome set
are found
Polyploidy
Infrequent in animal species but is well known in lizards, amphibians, and fish, and is
much more common in plants
Polyploidy
- Classified as either Autopolyploidy or Allopolyploidy
Polyploidy
addition of one or
more extra sets of chromosomes
identical to the normal haploid
complement of the same species
Autopolyploidy
combination of
chromosome sets from different
species occurring as a consequence of
hybridization
Allopolyploidy
- Polyploidy can arise in several ways
- Errors in meiosis during gamete formation
- Events at fertilization
- Errors in mitosis after fertilization
* Polyploidy can result from errors in mitosis or meiosis
- If homologous chromosomes fail to separate during meiosis I, meiosis II will produce a
diploid gamete.
Fusion of this diploid gamete with a normal haploid gamete will produce
a triploid zygote
polyploidy
It can also be produced at fertilization by the simultaneous penetration of a haploid egg
by two haploid sperm (dispermy). The resulting zygote contains three haploid
chromosome sets and is triploid
Polyploidy
The most common polyploidy
in humans, found in 15% to
18% of all spontaneous
abortions
Triploidy
- Approximately 75% of all
cases of triploidy have two
sets of paternal
chromosomes
Triploidy
Most triploid zygotes arise as
a result of
dispermy
It can result from a failure of cytokinesis in the first mitotic division after fertilization
Tetraploidy
- If tetraploidy arises sometime after the first mitotic division, two different cell types are
present in the embryo: ___
normal diploid cells and tetraploid cells
- Included in this broad category are deletions and duplications of genes or part of a
chromosome and rearrangements of genetic material in which a chromosome segment
is inverted, exchanged with a segment of a nonhomologous chromosome, or merely
transferred to another chromosome
hays auko na
Exchange and transfers are called _, in which the locations of genes are
altered within the genome
translocations
In most instances, these structural changes are due to one or more breaks
along the axis of a chromosome, followed by either the loss or
rearrangement of genetic material
new learining lang
The ends produced at points of breakage are “___” and can rejoin other
broken ends
sticky
If the breakage and rejoining do not reestablish the original relationship
and if the alteration occurs in germ plasm, the gametes will contain the
structural rearrangement, which is __
heritable
If the aberration is found in one homolog but not the other, the individual is said to be
__
heterozygous for the aberration
- In such cases, unusual but characteristic pairing configurations are formed during _
meiotic
synapsis
When a chromosome breaks in one
or more places and a portion of it is
lost, the missing piece is called a
_
deletion (deficiency
- The ___ can occur either near
one end (terminal deletion) or
within the interior of the
chromosome (intercalary deletion)
deletion
For synapsis to occur between a
chromosome with a large intercalary
deletion and a normal homolog, the
unpaired region of the normal homolog
must “___” into a deletion or
compensation loop
buckle out
If only a small part of a chromosome is
deleted, the organism might ___
survive
When any part of the genetic material,
either a single locus or a large piece of a
chromosome, is present more then once in
the genome, it is called a duplication
duplication
A type of chromosomal aberration in which a segment of a chromosome is turned
around 180 degrees within a chromosome
Inversions
An __ requires breaks at two points along the length of the chromosome and
subsequence reinsertion of the inverted segment
inversion
– the centromere is not part of the rearranged chromosome
segment
Paracentric inversion
the centromere is part of the inverted segment
- Pericentric inversion
Organisms with one inverted
chromosome and one noninverted
homolog are called inversion
____
heterozygotes
Pairing between two such
chromosomes in meiosis is
accomplished only if they form an
inversion loop
t or f
t
If crossing over occur within the
inversion loop,___
are produced
abnormal chromatids
When crossover occurs within a
paracentric inversion, one
recombinant ____ are produced
dicentric chromatid
(two centromeres) and one
recombinant acentric chromatid
(lacking a centromere)
Movement of chromosomal segment to a new
location in the genome
Translocation
Reciprocal translocation involves the exchange of
segments between two nonhomologous
chromosomes
Translocation
The genetic consequences of reciprocal
translocations are similar to those of inversions
Translocation
Genetic information is not lost or gained, there is
only a rearrangement of the genetic material
Translocation
The presence of a translocation does not directly
alter the viability of individuals bearing it
Translocation
Homologs that are heterozygous for
a reciprocal translocation undergo
unorthodox synapsis during meiosis
Translocation
the pairing results in a cross-like
configuration
Translocation
As with inversions, genetically
unbalanced gametes are also
produced as a result of this unusual
alignment during meiosis
Translocation
When breaks at the extreme ends
of the short arms of two
nonhomologous acrocentric
chromosomes occur, the small
segments are lost and the larger
segments fuse at their centromeric
region
Robertsonian
Translocation
This type of translocation
produces a new, large,
submetacentric or metacentric
chromosome, often called a
____
Robertsonian translocation
