Selasa, 05 November 2013

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What Are Chromosome, Mitosis and Meiosis

What are chromosome ? Chromosome is a microscopic structure carrying DNA molecule. In bacteria and arc bacteria, the chromosome (in DNA form) has ring- like structure that floats in cell plasma. In eukaryote, the chromosome is located reside nucleus. Eukaryotic chromosome has very complex structure and its DNA has strand-like structure.

Chromosome is composed of DNA and protein. Chromosome protein is called histone. In this matter, histone functions as coil of DNA. Histone's structure which is covered by DNA is called nucleosome.

Chromosome in most eukaryote consists of two primary structures, centromere and telomere. Centromere connects two chromatids (daughter chromosome). Generally, spindle (microtubule) attaches to centromere during mitosis and meiosis. Spindle will drive both centromere and chromosome towards proper location.

Telomere is a special DNA sequence which can be found at the end of chromosomes. Its function is to keep the Length of daughter chromosome constant just like the one inside the parents' cell. Scientists predict that telomere influences the activity of gene located nearby and also determine the longevity of a cell.

Chromosomes of living organisms that reproduce sexually are in pairs and called homologous chromosomes. One chromosome is bequeathed by male parent and the other chromosome is bequeathed by female parent. In the same cell, each chromosome pair is different one from another.

Based on the location of its centromere, chromosome is distinguished into several types as follows.

Metacentric chromosome is chromosome whose centromere lies in the middle of its arm.

Submetacentric chromosome is chromosome whose centromere lies closer to the middle of its arm.

Acrocentric chromosome is chromosome whose centromere is located quite near the end of its arm.

Telocentric chromosome is chromosome whose centromere is located at the terminal end of its arm.

Homotogous  chromosomes. Chromosome  pairs only  to its homologous. Sister chromatic  contains  identical gene, while  nonsister  chromatic  contains  gene bringing similiar  traits,  such  as hair  type and eye  color.

Every species has different number of chromosome in their body The total number of chromosome in nucleus is called genome. A cell consisting of two sets of chromosome is called diploid (2n). A cell consisting of three sets of chromosome is called triploid (3n).

Chromosome appearance in a cell is called karyotype. Scientists usually observe individual karyotype during metaphase of cell division.

The Number Of Chromosome In Living Organism

source:Biology, concepts & connections 2001

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