Essay
Applied scinece, biology, unit 11B
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This is distinction level work
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Voorbeeld van de inhoud
BiologyWhat is chromosome
A chromosome is simply a liner packed DNA -protein structure that is found in the nucleus of the cell
that houses the genetic material. In a eukaryotic cell, because the DNA strand is extremely long its
coils around a stabilizing protein called histone. The histone- DNA complex is called a nucleosome
and multiple nucleosomes is called a chromatin. The chromatin will wrap around each other to
produce an x shape structure called the x chromosome. There is a total of 46 chromosome in human
body with 23 of them coming from the mother side and another 23 of them coming from the father
side. Because they 2 sets of chromosomes (one from the mother and father) that makes the
organism a diploid cell . The chromosome contains many components which enable them to perform
many functions. These components are;
Centromere: the centromere is the narrow region of the chromosome that joins the sister
chromatid together but separates the p arm (shorts arm) from the q arm (long arm). During
cell division, the spindle fibres are attached to the centromere. The centromere is located in
the middle of the chromosome and it also from this region that categorise the chromosome
into 4 parts. There is no genetic code found in the centromere.
Chromatids: before cell division takes place, the chromosome will make a replica of itself
and the replicated chromosome will join the at the centromere. The chromatid is simple the
longitudinal half of the duplicated chromosome that contain one short arm and one long
arm. Genetically speaking, the pair of chromatids are identical unless a mutation has
occurred. During cell division in mitosis, the chromatids will split apart to formed their own
chromosome. The chromatids are important as it safeguard and stores the 2 copies of
genetic information which ensures that one of the genetic material goes to each daughter
cell. There are 2 categories of a chromatid which are sister chromatid and non-sister
chromatid
Sister chromatid: the sister chromatid are the 2 genetically identical copies of the single
duplicated chromosome. There are both joined together at the centromere and contain the
same alleles.
Non sister chromatids: non sister chromatid is simply when one of the 2 pairs of
chromosomes is inherited from the mother while the other pair is inherited from the
father. Meaning 2 chromosome contain 2 different genetic information.
Sex chromosome: in a human diploid cell, which is every cell in you body except from
reproductive cell. There are 2 version of every chromosome with one version being maternal
(mother side) while the other version is maternal (father side). They have the same genetic
material but not identical. This makes 2 set of 23 chromosome or 46 in total. In the last pair
of chromosomes, the 23rd pair, will determine the gender of the human. If the 23 rd pair of
chromosomes contain 2 x chromosome then the gender of the human is a female while if
the 23rd pair of chromosomes contain 1 x and 1 y chromosome then the gender of the
human is male. During meiosis 1, all egg cell can only have x chromosome because that all
there is in the parent cell of a female but sperm cell can end up with either a x or y
chromosome since there are both present in parent diploid cell in the male. The egg cell or
zygote that inherit 2 x chromosome upon fertilisation will become a female while the one
that get an x and a y upon fertilisation will become male.
, Autosomes: there are 2 set of 23 chromosomes or 46 in total and of those 23 pairs, there
are 22 pairs that are autosome. Autosomes are simply any chromosome that does not
influence that does not influence the sex of the organism but rather physiological
characteristic of the organism. In other words, there are 22 pairs of autosomes in the human
body and those autosomes contain genetic information that creates the dormant or
recessive trait of the human.
Chromosome number: the chromosome number is simply the number of chromosomes
typically found within an organism. For example, there are always 23 pairs of chromosomes
or 46 in total found in the human body, if there is an extra pair chromosome it shows that
something went wrong in cell division and the organism could experience an genetic
disorder. A popular example of this is down syndrome where the effected human received
an extra chromosome.
Homologous chromosome: a homologous chromosome is simply a type of chromosome that
is made up with a pair of chromatids that are identical to each other in term of size, genetic
information, and shape. 22 of the 23 pairs of chromosomes are homologous. In sexual
reproduction, the parent contributes to one of each pair of chromosomes but contain
different version of genetic information. These different versions are called allele. Those 2
sets of chromosomes come together to form the characteristic of the off spring
Non-homologous chromosome: a non- homologous chromosome is simply a type of
chromosome that does not have a matching partner chromosome with similar size, genetic
information and shape. Non homologous chromosome is unique and does not have a
correspond matching chromosome. These types of chromosomes are typically found in
organicism that reproduce asexually as only one set of chromosomes is passed down to the
offspring.
, What is mitosis
Mitosis is a type of cell division that occur in some eukaryotic cell which result in the creation of 2
identical daughter from a single parent cell. During mitosis, the chromosome found in the nucleus
are duplicated and the 2 copies of DNA are separated even to form a complete set of
chromosomes. The evenly separated copies of DNA are called the daughter cell. There are 4 stages
in mitosis which are
1)Prophase
Prophase is the fist stage in mitosis. Proceeding the s phase, chromosome found inside the nucleus
have been duplicated to produce 2 sister chromatids. One of the changes that you will immediately
notice is that the chromosome becomes more visible to the eye or more condensed, this is due to
the super coiling of the DNA with in chromosome. During the prophase, the nucleolus disappears
and the nuclear envelope which surround the nucleus that keeps cytoplasm starts to disintegrate.
Because of this, it allows the chromosome to move freely. Another event that occurs, is the
production of mitotic spindle or spindle fibre which are long, thin microtubules made up of protein.
These mitotic spindles help in pulling apart the chromosome during cell division. As the prophase
continues the centrosome, a small structure that organise and connect to the mitotic spindle, that
moves to the opposite sides of the cell. This ensures that the chromosomes are equally distributed
between daughter cell. The chromosome will start producing a protein complex called a kinetochore
at the centromere. The mitotic spindle will capture the free flooding chromosome via the use of the
kinetochore. Each chromosome will have 1 spindle fibres connected to each chromatid at the
centromere.
2) metaphase
Metaphase is the second stage of mitosis. At this staged the chromosomes are completely visible.
Each chromosome is made up of 2 genetically identical sister chromatid that are held together by
the centromere and at the centromere there are 1 spindle fibre connect to each of the chromatids.
The other end of the spindle fibre is connected to a small structure called a centrosome, which
moves to the opposite sides (poles) of the cell. as the centrosomes moves to the poles, the
chromosome will align at the middle or equator of the cell which will result in a sister chromatid on
either side of the equator. At this stage, there is a inspection point known at the M checkpoint that
will check if each matching set of sister chromatids is tightly secured to opposite end of the mitotic
fibre. Once all the kinetochores are attached to the spindle, a regulatory protein complex is activated
permitting the cell to move through m checkpoint thus leading to the 3 rd stage of mitosis. When the
chromosome align in the centre or equator of the cell is called a metaphase plate. There will be
excess mitotic spindle at formed behind the centrosome called the aster microtubules which will
attached to the membrane of the cytoplasm.
3)anaphase
Anaphase is the 3rd stage of mitosis. a special anaphase promoting complex (APC) called separase
breaks down the protein that link the sister chromatid at the centromere. As the centromere splits
apart, the 2 sister chromatids are pulled in the in opposite direction. Once separated each sister
chromatid is now called chromosome. These chromosomes have a motor protein attached to the
kinetochore of the rears them in to the opposite sided of the cell by their centromere. As they are
being reared in, the mitotic fibre breaking apart as they proceed. During the anaphase, another
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