Chromosome variations
1. Metacentric. The position of the centromere is located in the middle of
the chromosome so the chromosome has two arms with a length of more
or less the same.
2. Submetacentric. The centromer position lies in the position of one part of
the chromosome, produces chromosomes with one of the chromosome
arms longer than other chromsomom arms.
3. Acrocentric. The centromer is located almost the end of one end of the
chromosome, so the chromosome with one chromosome arm is beat and
a small piece (knob) or satellite at the other end.
4. Telocentric. The centromer lies at the end or almost the end of the
chromosome.
Modification of chromosomes can have an effect not only in changes in the total
number of chromosomes, but can also cause chromosome structure changes
because of the deletion event, duplicate the chromosome segment or genetic
germeerial settings on the chromosome itself or involving other chromosomes
Broadly speaking, the change of chromosomes is distinguished into three large
groups, namely: Chromosomal Rearrangement, aneuploidi and euploidi.
Variations in the number of chromosomes
Variations of the number of chromosomes can be caused by additions or
reducing the number of chromosomes or the number of chromosome
devices.
Changes in the number of chromosomes by reduction or the addition of
the number of chromosomes are commonly referred to as aneuploidi,
while changes in the number of cromosomes are categorized by the
Euploidi group chromosome mutation.
Some types of aneuploidi that can be found in nature include:
1. Nulisomi. A situation in which individuals are free of homologous
chromosomes. This condition is indicated by the 2N-2 formula, where n
refers to the number of status of haploid chromosomes.
2. Monosomi. A situation when the individual loses a single chromosome.
Dototed with 2N - 1. For example, human zygot monosomy conditions
have a number of chromosomes 45.
3. Trisomy. The situation where individuals get an additional single
chromosome. This condition is denoted by 2N + 1. Trisomy example in
humans is the addition of a chromosome 21 to the individual down
syndrome, so the total number of individual down syndrome
chromosomes is 47.
4. Tetrasomi. The situation where individuals get an additional pair of
homologous chromosomes so the number of chromosomes becomes 2n +
2.
Aneuploidi events occur because of abnormal events during formation of
gamets both in Dispertifying meiosis I, meiosis II or even mitosis.
The homolog chromosome pair failed to separate himself towards the
polar position of the cell during the division occurred. As a result, there
are cells that get more chromosomes but on the contrary there are cells
that lack the number of chromosomes.
The event failed to separate him of homologous chromosome when the
formation of the gamet was called the event failed to separate or non-
disjunction.
Events failed to separate occur not only in humans but can occur in all
organisms. In human down syndrome caused by trisomy 21, from the
results of the research in the village is associated with a gestational age of
the mother. The frequency of events failed to split correlated with
gestational age. This means that the older age of a mother, the incident
tendency to fail to separate which triggers the case of Down Syndrome in
the fetus which is contained significantly.
Changes in the number of chromosomes can be in the form of changes in
the number of devices / chromosomes or called euploidi. Basically we
have often found evidence of euploidi this is for example in seedless
watermelon. Seedless watermelon occurs because the formation of
embryos in watermelon seeds cannot run normally due to abnormalities
in the process of forming the gamet due to non-disjunction. So Zigot does
not develop and seeds do not develop leaving the fruit as if not seeded.
In most eukariot organisms, the number of chromosomes is diploid (2N),
but there are times when there is an error in the process of mitotic or
meiosis division which causes the doubling the number of chromosomes
or commonly referred to as polypoidi.
Polyploids can be triploid (3n), tetraploid (4n), pentaploid (5n) or more.
Poliploidy conditions are found in many plants, at least around 40% of
flowering plants in the condition of the polypoidi of the 70-80% grass-
pancutaneous grass also experiences pollidi. In plants the polyploidy
conditions are related to evolutionary events, where plants have flexibility
in the number of chromosomes that are better than animals. For example,
the formation of modern wheat that is currently available, is basically the
result of a natural cross between several wild wheat species and grass - a
lot of different chromosomes.
In animals, failure formation of gametes due to the incompatibility of the
number of chromosomes during cell division, causes the eggs fertilized by
sperm by the number of different chromosome devices or vice versa, will
result in the failure of the growth of the formed zygote. However, some
invertebrates, Salamanders, fish and frogs are known to also experience
polyploidy.
Variations of chromosome structures
Chromosome rearrangement is one form of chromosome structure. There are
several types of mutations this type including:
1. Duplication.
Cromosome duplication occurs when there is a part of the
chromosome that experiences multiplication.
Changes in the structure of the chromosome in the form of
multiplication of the chromosome segment will ultimately facing the
problem of problems, especially in gametes formed. Duplication
occurs when cells do division, there is a phase where the chromosome
will carry out the maximum alignment (alignment) with homolong
chromosomes and non-homologous chromosomes form a tetrad
structure.
There are times when the alignment process does not go well so that
the non-homologous chromosome becomes not aspursed. If followed
by a cross-switching process, it will cause unequal crossing over (Cross
Moving Not Settlement) and the consequences are in addition to the
resulting chromosomes that experienced segment duplication also
produced chromosomes that experience reducing chromosome
segments (deletions).
2. Delesi
When a chromosome has broken in one place or more and the part of
the fault is lost, the chromosome experiences deleti events.
Humbilian chromosome fragments due to deletions can occur in parts
that involve loss of centromers or not.
The loss of centromere because of the deletion's event, it will cause
chromosome inability to bind to spindle thread during the cell division
process. As a result the chromosome without centromer will disappear
and not inherited.
If the part of the fragment is missing is not large due to deletions,
individuals who experience it may still be able to survive. But in many
cases, the effects of deletions do not have to involve the loss of a large
enough part of the chromosome.
If the missing part contains functionally important genetic
information for the lives of the organism, the effect of the small part of
the delession will also affect the process of the development of the
organism even in some cases can be letal. One example of syndrome in
humans that occur due to the deleti chromosome mutation is CRI-Du-
chat Syndrome. Individuals who suffer from the syndrome are caused
by the presence of deletions at the end of the number 5. The syndrome
is originally categorized as a monosomous chromosome mutation, but
because the missing part of the number 5 chromosome is only a small
part, then This syndrome is categorized as a deletion mutation with
46.5p- chromosome annotation. Cri-du-chat syndrome sufferers have
special phenotypical features, namely the sound of crying that
resembles a cat's voice.
Delesi on chromosomes can be easily detected from shortening
chromosome arms. If this happens, it is in heterozygous conditions, at
the time of alignment in the default phase (meiosis i), the chromosome
will be seen forming a loop to maximize the alignment process. This
happens because one chromatin of the chromosome is shorter than his
partner.
3. Inversion
Another chromosome structure mutation was in the form of the
charming linear structure of the chromosome due to the broken event
of the chromosome segment in two locations and followed by the
interpretation / inversion (180o) of the chromosome fault for the
following resume.
The effect is the formation of a new linear sequence that is reversed
when compared to the order of the original chromosome. This type of
mutation, does not cause lost or increasing chromosome fragments,
only a new rearrangerment of the chromosome structure.
Inversion mutations can involve centrometers in reversal of the order
of chromosome structures or do not involve it. If the centromere is not
involved in the reversal / inversion process of chromosome fragments,
then this inversion is called parasid-inversion. Conversely, if the
reversal / inversion involves the centromacy, called a periscentric
inversion.
Parasid inversion. In this inversion, faults in the chromosome
fragments occur in the part of the centromaire. When inversion occurs
and rearrangement is complete, the position of the centromere of the
chromosome does not change. Changes only occur in the converted
fragment section.
Perisentric inversion. In this inversion, the broken chromosome
fragments occur in a position that involves the centromair in the
middle. As a result, when inversion has finished, chromosomes
experience changes in the position of the centromere, especially if it
involves the position of the fault not balanced between the right and
left position of the centromacy.
Although the effect of the inversion chromosome mutation is classified
as having a minimal effect on the oganism that experiences it, the
organism that has heterozygous status for chromosome fragments that
experience inversion will have a significant impact especially in the
formation of gamet. Abnormal gametes will be formed which means
the effect of inversion mutations can have a significant impact on
individual descendants who experience inversion mutations.
The effect of the rearrangement of chromosomes due to inversion will
be seen in heterozygous individuals for fragments that experience
inversion mutations. But this effect will be visible and appear when
followed by cross-transfer events. When heterozygous chromosomes
pair in the position of Tetrad, then one of the homologous
chromosomes experiences an inversion mutation, the alignment
process / second-terms of homologous chromosomes will be carried
out and produce a loop.
This loop is formed to anticipate that the second alignement process of
the homologous chromosome occurs optimally. In this process
followed by cross-moving events, where cross moves can occur in the
loop or outside the loop. If a cross moves outside the fragments that
experience inversion, which means crossing the cross outside the loop,
the formed gamet will have a normal order and structure of
chromosomes. But if a cross moves occurs in the fragment that
experiences inversion, or in the loop section, it will be formed by
abnormal gamets. Among them will be produced by chromosomes that
have 2 centromers (disentric) and chromosomes that do not have a
centromair (asentric). Both of these types of chromosomes will cause
gamet to become abnormal and gamet does not develop.
4. Translocation
Translocation is a type of chromosome mutation that involves moving
fragments of a chromosome to other parts of the same chromosome or
moving to other non-histomologist chromosomes. The process of
displacement of fragments in transformed transformed with fragment
exchanges between homologous chromosomes in cross-transfer
processes.
Translocation is divided into 2 namely non-resipal translocation and reciprocal
translocation.
1. Non-resipal translocation, occurs when the transfer of
chromosomal fragments is not accompanied by a reciprocal
exchanging fragment from the goal chromosome. For example two
non-homologous chromosomes with the sequence of ab.cdefg and
chromosomes mn.opqrs. Reciprochal translocation occurs in the
ab.cdefg chromosome, where the EF fragment moves to non-
homologous chromosomes mn.opqrs. Will be produced by ab.cdg
and mn.opefqrs chromosomes.
2. Resiprocal translocation, more common than non-resipal
translocation. On reciprocal transportation, fragment exchanges
occur between the two non-homologous chromosomes. For
example in chromosomes in the order of the above, ab.cdefg and
chromosome mn.opqrs, if resprokal translocation occurs in the
fragments of EF and QR, the chromosomes will be formed with the
sequence of ab.cdqrg and chromosomes mn.opefs.
Translocation chromosome mutations can bring up the effects of
organisms that experience it assuming that the fragments that
experience translocations of moves at different chromosome locations
can cause changing regulation of gene expression which happens to lie
in the fragment. Another thing, the broken location of chromosomal
fragments can cause damage to the order of genes that happen to lie in
the location of the fault occur.
Translocation chromosome mutations are thought to be one proof of
evolution at the chromosome level which causes the emergence of new
species of primates. Translocation which is generally followed by
Delesi events, becomes one of the tools of attracting genetic and
evolutionary fields. Robertsonian translocation as an example, in the
translocation event of a long-sleeve of two acrospeult chromosomes,
led to a new metascentric chromosome with a long-sleeved arm and an
acentric chromosome fragment.
Robertsonian translocation is also interesting for genetic researchers
and evolution, because through the translocation mechanism of
Robertsonian this evolution of human karotype, gorilla, chimpanzees
and orangutans can be explained. The number of chromosomes in the
gorilla, chimpanzees and orangutans is 48 while in human
chromosome people are 46. What's interesting, number 2
chromosomes in humans, metascentric chromosomes, have a long
arm size. In addition, the G banding pattern (chromosome staining to
see the line pattern on the chromosome) on the chromosomal arm
number 2 human has a pattern that is identical to the pattern of G
banding 2 different assentric chromosomes in the ape group above. It
was alleged that the Robertsonian translocation mutation occurred in
the human ancestors involving 2 Asentric Chromosomes.
