Chromosome - Biology Notes

Chromosome The term chromosome was introduced by W. Waldayer who said that chromosome comes from two words, namely chroma which means colorand soma means body. 1. Properties of Chromosomes The properties of chromosomes are:  Only visible when cells divide.  Has a length between 0.2 – 40 m (microns).  Chromosomes in prokaryotic cells only have one chromosome and not located in the cell nucleus.  Eukaryotic cell chromosomes, the number varies according to type organisms and is found in the nucleus.  Generally has a chemical composition consisting of 60% chromatin,35% protein, DNA and 5% RNA.  Proteins consist of histones and nonhistones (neutral or acidic).  Has several enzymes involved in DNA and RNA synthesis. 2. Classification of Chromosomes Based on their type and function, chromosomes are classified into two types, namely: a. Autosomal chromosomes (body chromosomes), namely chromosomes that are not has something to do with gender determination. b. Gonosomes (sex chromosomes), namely a pair of chromosomes that determine sex, are generally divided into two types, namely the X sex chromosome and the Y sex chromosome (for example in humans). The entire chromosome in an individual or species is called the genome.A normal adult female has 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes (XX) and her chromosome formula is 22AA + XX or 44A + XX. Normal adult males have an X chromosome and a Y chromosome and 22 pairs of autosomal chromosomes. The chromosome formula is 22AA + XY or 44A + XY. Based on their location in an individual, chromosomes are divided into 2, namely:  Prokaryotic chromosomes, namely chromosomes that and only found in prokaryotic organisms. For example: chromosome in tobacco is only a single ARN chromosome in E. coli bacteria is a single ADN thread followed by an ARN molecule. are very simple the mosaic virus band and the that is coiled or  Eukaryotic chromosomes, namely chromosomes found in multicellular organisms. In general, it consists of two very long ADN bands (sense and antisense) and is covered by a nuclear membrane. 3. Chromosome Arrangement The parts of a chromosome are:  Centromere (kinetochore) It is a link between one chromonema and another and functions as a place for attachment of the spindle threads when the chromosomes move towards the cell poles, in the anaphase phase of chromosome division.  Chromonema Spiral shaped ribbon, place attachment of chromiol and chromomer.  Chromomeres (large granules) The chromonema is thickened in several places and is the nucleoprotein material that settles as well as the location of the gene locus.  Chromiol (small granules) Chromosomes are slightly thickened.  Telomeres The part that is found at the end of the chromosome and functions toprevents the joining of chromosomes to one another.  Matrix Cytoplasmic fluid (endoplasm) which is slightly condensed and is found in the chromosomes.  Gene locus The part that functions as a carrier of hereditary traits (heredity).  Satellite Additional parts are found at the ends of chromosomes and each chromosome does not necessarily have them.  Membrane (membrane) The thin layer that covers the chromosomes. 4. Types of Chromosomes Based on the position of the centromere, chromosomes are classified into 4 types, namely:  Metacentric, when both chromosome arms are the same length and the centromere is in the middle at the same distance.  Submetacentric, if the two chromosome arms are not the same length and the centromere is not in the middle (closer to one of the arms).  Acrocentric, when one arm is very short compared to the other arm so that the centromere is very close to one of the arms.  Telocentric, if it only has one arm and the centromere is located at the end of the chromosome. 5. The Role of Chromosomes in Inheritance of Traits According to Mendel's law, genes in chromosomes are found in pairs and the members of the pair are obtained from the parents. During meiosis, the pairs of chromosomes separate and only one member of each pair moves to the sex cells.