When asked further, how it appears or looks like in the cell? Can you draw a picture of the chromosome?
They draw the typical picture showing two chromatids joint at centromere.
There is a big flaw in defining the
chromosome. There is no text available that can snapshot the in depth true
picture of the CHROMOSOME.
The term CHROMOSOME has
been misused. There should have been some restriction on using the term at
wrong place. With rare exceptions most of the authors use the term CHROMOSOME very
liberally.
That causes confusion among the young learners. I can give many examples of mishandling of the term chromosome but that is not our purpose at the moment.
That causes confusion among the young learners. I can give many examples of mishandling of the term chromosome but that is not our purpose at the moment.
Le t we start with one example, what biology online says
about Chromosome.
Biology online
Definition
noun, plural: chromosomes
A structure within the cell that bears the genetic material as a threadlike linear strand of DNA bonded to various proteins in the nucleus of eukaryotic cells, or as a circular strand of DNA (or RNA in some viruses) in the cytoplasm of prokaryotes and in the mitochondrion and chloroplast of certain eukaryotes.
Supplement
In eukaryotes, the chromosomes
appear as threadlike strand that condense into thicker structures and aligns on the metaphase plate during mitosis. Humans normally
have 23 pairs of chromosomes, each with a characteristic length and banding
pattern. Chromosomes occur in pairs (in most somatic cells) since one member of
each pair comes from the mother and the other from the father. In most prokaryotes, the chromosome is
usually a circular strand of DNA; hence, the entire genome is carried on only
one chromosome. In viruses, the chromosome may
appear as short linear or circular structure containing the DNA or RNA molecule often lacking any
structural proteins.
Word origin: from the Greek chroma = color + soma = body.
Now look at biology online basic definition
(without supplement)
Definition
noun, plural: chromosomes
A structure within the cell that bears the genetic
material as a
threadlike linear strand of DNA bonded to various proteins in the nucleus of eukaryotic cells, or as a circular strand of DNA (or RNA in some viruses) in the cytoplasm of prokaryotes and in the mitochondrion and chloroplast of certain eukaryotes
Let we scrutinize it:
Chromosome in eukaryotic cell:
It is a structure in the nucleus.
It is a structure that
bears genetic material.
The structure
bears the genetic material as a thread like linear strand of DNA bonded to various proteins.
Chromosome -In prokaryotic cell:
It is a structure in the cytoplasm.
It is a structure that
bears genetic material.
The structure
bears the genetic material as a circular strand of DNA.
Chromosome In some viruses-
-As a strand of RNA (of course in other viruses
as a strand of DNA)
Chromosome In mitochondrion and chloroplast
of certain Eukaryotes-
- As a circular strand of DNA.
Adding supplement to definition
serves nothing but further supplements the confusion.
All this makes the chromosome definition a blurry thing. It neither
fixes its structure nor the chemical composition.So chromosome is a very vague term used by biologist. Bear in
mind it has different meaning at different places.
Is there any solution to clear this mess?
Yes, I have been working hard to make it
simple and clear.
But I wish to know, how many people are interested?
If anyone happens to visit this blog and feels that
confusion must be cleared, please comment.
I will write further in detail.
I will write further in detail.
