A. UNDERSTANDING
THE DEFINITIONS OF CHROMOSOMES
"Chromosome" is derived from two words,
"chroma" which means thread, and "soma" meaning body. As
the name implies, the chromosome is a structure in the form of threads that
carry genetic information (genes). Chromosomes is in every living cell nucleus.
Gene is the genetic material that has information which will be passed on from
parent to their child. In the chromosomes, genes are stored in a special area
called the locus. Gene pairs in the locus are called alleles. Body chromosome
is made by threads of chromatin prepared by nucleic acids (DNA and RNA) and
protein. The composition is 60% protein, 35% of DNA, RNA and 5%.
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| CHROMOSOMES |
Every living thing has a different number of
chromosomes. Humans have 46 chromosomes (23 chromosomes come from the father
and 23 chromosomes from their mother) in each nucleus. Here is the Number of
chromosomes in some species :
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| NUMBER OF CHROMOSOMES IN SOME SPECIES |
B. THE
FUNCTION OF CHROMOSOMES
There are three main functions of chromosomes :
- As a storage of genetic information that will be passed down from parent to child that shape the nature and characteristics of the individual.
- Plays an important role in the process of cell division.
- Determining the sex of an individual.
B. THE
STRUCTURE OF CHROMOSOMES
DNA together with proteins called histone proteins will
form structures called nucleosomes.
Then a group of nucleosome will form a nucleosome threads called chromatin. A collection of yarn wrapped
chromatin will form chromosomes. Before the onset of cell division, DNA of each
chromosome splits to form the double arm called chromatids. This DNA replication function is to make sure the child
cells will get a complete copy of the genetic information of its parent.
Based on the results, cell division will form two
types of chromosomes, namely:
- Diploid Chromosome, a cell that has two sets of chromosomes, diploid cells are identical (homologous) genetically with stem cells. Diploid cell has the same number of chromosomes as their parent.
- Haploid Chromosome, are the cells that have only one set of chromosomes, haploid cells are not identical (non-homologous) genetically with stem cells. Haploid cell also has only half the number of chromosomes of the parent cell.
To understand more about the structure of chromosomes
we have explained above, look at the picture below:
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| CHROMOSOME STRUCTURE |
C. PARTS OF
CHROMOSOME
In general, the entire chromosome has two parts of
the body, namely the centromere and arms chromosomes (chromatids).
1. The
centromere
The central part of chromosomes that is generally
spherical. At the centromere there is a component called kinetochore, this
kinetochore function are important when the occurrence of cell division. In
this part, spindle thread attached to each of the opposite pole.
2. Chromatids
Chromatid is one of the arms results in chromosome
replication. On chromosome arms are kromonema, a ribbon-shaped component. In
kromonema, can be seen a thickening in the form of beads called Kromomer.
Kromomer generally difficult to observe, but can be seen clearly on a
chromosome that has many replication. Kromonema wrapped by a special substance
called a matrix. Chromatids are attached to each other at the centromere.
3. Telomeres
Telomere is a term used to indicate the end of a
chromosome. Telomeres function to keep the ends of DNA to not decompose and
prevent the meeting of one arm with the other arm of the chromosome. Telomeres
also serves to protect the chromosomes from environmental threats.
D. TYPES OF
CHROMOSOME
1. Functions
Based
According to its function, the chromosomes are
divided into two types:
- Autosomal Chromosome (Body), which is chromosomes that provide characteristics that exist in living bodies. Examples: humans have 22 pairs of chromosomes autosomes and one pair of chromosomes genosom.
- Genosom Chromosome (Gender), the chromosome that determines the sex of organisms owner. For example, humans have one Genosom chromosome pairs, If one pair of chromosomes are XX, the gender is female, but if the pair of chromosomes are XY then the gender is male.
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| TYPES OF CHROMOSOME |
2. Based On
The Location of Its Centromere
Based on the location of the centromere, chromosome
are divided into four, namely:
- Talocentric, a chromosome that the centromere is located at the tip of chromosome arms.
- Metacentric, a chromosome with the centromere is located right in the middle of the chromosome arm.
- Acrocentric, a chromosomal location of the centromere is near the end of one arm of the chromosome.
- Submetacentric, a chromosomal location of the centromere is located almost in the middle of the chromosome.
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| TYPES OF CHROMOSOME |
3. Based on
the number of centromere
Based on the numbers of centromere, Chromosomes are
divided into four, namely:
- Acentric, the chromosomes do not have centromere.
- Monocentric, chromosome which has only one chromosome.
- Dicentric, chromosome has two centromeres.
- Polycentric, chromosome has many centromeres (more than 2).
