what is the difference between 2n & 2c about chromosome plz explain
Answers
Terminology Chromosomes/chromatids
As help file for the understanding of the webpages on the cell cycle a number of terms and facts related to chromosomes and chromatids are highlighted here:
chromosomes, chromatids, sister chromatids, homolog chromosomes and centromeres
Chromosomes and chromatids occur as rod or thread-shaped structures in the nucleus of eukaryotic cells. Prokaryotes usually have only a single circular chromosome (in the webseries we will not focus on this group). The name chromosome (from the Greek chroma = color and soma = body) originates from the fact that chromosomes can be observed as stainable bodies in a light microscope during cell division.
Chromosomes and chromatids contain chromatin, which mainly consists of extremely long stands of DNA material (Deoxyribonucleic acid) that functions as carrier of genes and regulatory elements. Besides, chromatin contains Histones (chromosome proteins) and other proteins involved in the packaging of the DNA strands during condensation at cell division (see figure E here below) and small quantities of RNA. aantallen chromosomen, chromatiden, zusterchromatiden, homogole chromosomen, ploïdienumber of chromosomes, chromatids, sister chromatids, homolog chromosomes, ploidy
Sister chromatids (with -tid at the end), are two identical (= exactly the same) parts (Chromatids) arising from replication of a chromosome. (In the figure here next the sister chromatids A1 and A2 are an exact copy of each other, as well as the set B1 and B2, whereas homologs A's and B's show small differences). These two parts retain the denomination chromatids as long as they are bound together through the centromere, which is for example the case during the entire S phase following duplication of DNA (replication). This connection is vible as a constriction during mitosis or meiosis. During anaphase in mitosis and anaphase II in meiosis the two sister chroamtids are pulled apart at the centromer. According to current definitions, each single chromatid is regarded as a own chromosome after separation of the chromatids during cell division.
In most organisms chromosomes occur in pairs, the so-called homolog chromosomes (homolog = similar/corresponding). In contrast to the sister chromatides the homolog chromosomes consist of two (slightly) different copies of the same chromosome; homolog chromosomes carry yet the same genes, but the two copies of each allel can be either identicalor different of each other.
A single chromosome contains only on single long unbranched double-stranded DNA molecule that displays the typical double-helix structure. This double-strands DNA is formed by one phosphate group alternating with one desoxyribose group coupled to each other by nucleic acids (adenine, guanine, thymine en cytosine). These nucleic acids form consistent pairs (AT and CG). Of each complementary strands of the DNA molecule the antisense can be read (used as a template) for the synthesis of proteins, but not the sense.
The ploidy refers to the number of different copies of each chromosome present in a cell. Most plants and animals are diploid, indicated by 2n, which means that there are twocopies of each chromosome per cell. Their gametes, however, are haploid, indicated by n (one single copy). Bacteria and some plants and fungi are haploid organisms.
The number of chromatids or chromosomes coding for the same (corresponding) genes within a cell, is sometimes indicated by the small letter c. For example, a cell that was 2c before replication, will become 4 c after replication, thus when the DNA has been doubled in preparation of mitosis, because four samples of DNA stands coding for the same genes are present, but the ploidy will remain unchanged: if the cell was 2n, it is still 2n after replication and it was 4n it remains 4n.