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What are Chromosomes?

As we know about how important is DNA i.e. DeoxyRiboNucleic Acid in passing characteristics from one generation to another. It acts as a blueprint for a living thing and codes for proteins. It is a spiraling chain-like molecule that is made up of 4 different types of nucleotides. Namely A, T, C and G. 

We have also learnt that DNA is present in genes and how do we define a gene? A gene can be defined as a long stretch of DNA that codes for usually a protein or a group of proteins, also considering a few exceptions. In human beings or other multi-celled creatures, the proteins that are coded by genes interact with other proteins and molecules thereby making up living cells. These cells make up tissues that make up organs and organs entirely make up living creatures. Different kinds of genes lead to different traits in living organisms also due to differences in genetic coding or mutations. The mutation is any change in the nucleotide sequence of a chain of DNA or RNA (Ribonucleic Acid).

Knowing all of this information, we will move further with the chromosome definition and how it is related to the above.

Who Discovered Chromosomes?

The first person to discover Chromosomes was Strasburger in the year 1815 and Waldeyer used the term 'chromosome' in the year 1888. 

Chromosome Definition

A chromosome can be defined as an entire chain of DNA and it comes along with a group of stabilizing proteins. Chromosomes seem to be thread-like in appearance and are located inside the nucleus of an animal and plant cells. As discussed above, each chromosome is made up of protein and DNA (a single molecule). And as we already know the function of DNA in passing unique characteristics from parents to offspring, it contains specific instructions that make each type of living organism. And here, we can highlight the chromosome function which is to carry this basic genetic material known as DNA and it is essential for growth, survival, development and reproduction which is performed by various cells.

The thread-like structure in the chromosome is referred to as chromatin fibre and is arranged in the chromosome in such a manner that the chromosome looks like a spool of yarn. This chromatin fiber is a collection of protein molecules called histones that are wrapped with a string-like structure. If we zoom in the string we can find there is a chain of DNA in it which is extremely long with millions of nucleotides and contains hundreds of genes along its length. 

Chromosome Structure

The ultrastructure of the chromosome can be briefly explained as- it consists of a single very long DNA that is compacted approx 10,000 fold by interactions with proteins. This structure fits within a eukaryotic nucleus of only 10 microns diameter.

During the reproductive stage, the chromosome is tightly packaged and helps with durability during the splitting of the cell into two. In most of the other cell’s life, chromosomes are present as a loose and noodle-like structure accompanied by other chromosomes and inside the nucleus of a cell. There are 23 pairs of chromosomes in the human genome, making it 46 altogether. There are a few exceptions where each cell in the body consists of its full copy of our chromosomes.

The eyeball cells will make use of only the eyeball cell genes and the rest are turned off.  Liver cells use only live cell genes and the rest are turned off. Similarly, this is applicable for each cell type. 

In humans, one member from each pair of chromosomes comes from the mother and the other comes from the father.

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Let’s Understand All the Parts of the Above Chromosome Structure One By One:

Centromere: It is also known as Kinetochore and is the primary constriction at the center where the chromatids or spindle fibers are attached. It functions in the movement of the chromosome during a stage called anaphase during cell division.

Chromatid: When a chromosome is divided into two identical strands during cell division, a chromatid is formed as half of the chromosome. Each half strand is joined by a centromere, both are known as sister chromatids; and it contains DNA and separates at Anaphase to form a separate chromosome. 

Chromatin: Chromatin is a complex of DNA consisting of DNA, RNA, and protein and it forms chromosomes within the nucleus of eukaryotic cells. It doesn’t exist freely as linear stands, rather it is highly condensed and wrapped around nuclear proteins.

Telomere: The terminal region of each side of the chromosome is called a telomere. 


Chromosome Function

Chromosomes carry the basic genetic material DNA which is responsible to provide hereditary characteristics and genetic information to the various cells. The cellular functions are important for the growth and survival of living organisms.

Talking about the chemical composition of chromosomes, they are covered by histones and other proteins whose role is protection from chemical enzymes and physical forces. This, in turn, helps DNA to have a safeguard during the process of cell division.

Non-histone proteins present in the chromosomes help in the regulation of gene action. 

Knowing about the chromosome structure and function, we can say that the chromosome shape appears like a butterfly with a centromere in between. Actually, its shape depends on the location of the centromere which is different at each stage of the cell division. Example- The X-shape structure of the chromosome is found at the metaphase stage.

How To Make Notes on Chromosomes

  • Go through Chromosome - Definition, Structure, Function and Important FAQs on Vedantu

  • Read the page carefully and then highlight all the important portions

  • Try to understand whatever has been explained instead of just mugging it up

  • Write down in your own words and make mini notes

  • Follow the sequence that’s on the page so as to learn in an organized manner

  • Go through what you’ve written and then revise everything before the tests

  • Do not copy-paste what’s on the page

  • Re-read those areas that require more understanding

  • Draw some pictures if you need to memorize certain things as pictures tend to get retained in the memory more

  • Write brief sentences

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FAQs on Chromosomes

1. How can students learn about DNA before their tests?

DeoxyRibonucleic Acid. It is like a map for living beings and a code for proteins.  DNA is present in genes. A gene is a long stretch of DNA that codes for a group of proteins. It has been elaborated upon on the above-mentioned page. Reading this page will clarify all doubts that the students have regarding DNAs. They must also revise from this page before they sit for tests as that will cover all those areas that have been unknowingly missed.

2. How can students perform well in a test on Chromosomes?

All students who need to learn about Chromosomes must go through  Chromosome - Definition, Structure, Function and Important FAQs on Vedantu. This page has explained Chromosomes in detail and is quite useful before the main exams. Chromosomes can be tricky to understand but once the basics are understood, the rest of the concepts make perfect sense. A chromosome is an entire chain of DNA. It comes together with a group of stabilizing proteins. Chromosomes can be quite scoring if the concepts have been explained.

3. What is a telomere?

The terminal region of each side of a chromosome is known as the telomere. This page is appropriate in terms of studying for Chromosomes. Students must be careful while making notes and revising from this topic as any error or misinterpretation could lead to factual inaccuracies during the tests. If they wish to score well, they must be thorough with all the concepts.

4. Is it possible for students to complete their Biology papers on chromosomes?

It is possible for students to complete all their papers well before time if they are well practised. Sitting for tests at home and then assessing oneself is an effective way of doing so.  Timing is important and must be stuck to while students write papers at home. They can also read from Chromosome.

If they regularly make it a habit to practise papers, they will be able to complete those on time and get rid of the anxiety that they are surrounded with. Appearing for tests with a relaxed mind will help students secure higher marks. Thus, students must regularly practice sample papers to revise the topics.