Understanding Chromosomes and Chromatids: Definitions & Functions
Chromosomes are thread-like or rod-shaped structures present in cellular organisms that consist of DNA information. In the eukaryotic organisms, they are present in the nucleus of the cells, whereas, in the prokaryotic organisms, there is just one ring-shaped chromosome, commonly known as the genopore. Chromosomes have genes that contain the hereditary information of that organism.
One chromosome contains two similar structures that are held together at a point called the centromere. Each of these is referred to as a chromatid. Hence, one chromosome has two chromatids that are connected by a centromere. Chromosomes, therefore, possess an X shape. The study of cell division and chromosomes is referred to as cytogenetics.
Structure of Chromosomes
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Structure of Chromosomes
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The above structure is a simple diagram of the chromosome. However, the prokaryotic and eukaryotic cells have a different chromosome structure. But they are similar in many ways. The similarities between the prokaryotic and eukaryotic chromosomes are given below.
Both the prokaryotic as well as eukaryotic chromosomes have DNA, which is the genetic information.
The negatively charged DNA which is present in both the types tends to react with the positively charged proteins for neutralizing their charges.
The genetic material in both the chromosomes contains the coding as well as the non-coding sequences.
DNA methylation in both chromosomes is responsible for DNA activation.
Both of these groups have extra-chromosomal genetic materials. The DNA of mitochondria and the chloroplasts in the case of eukaryotes, and plasmids in the prokaryotes.
The Difference Between The Prokaryotic and Eukaryotic Chromosome Is As Follows -
The genetic material in eukaryotes is properly organized in the form of distinct structural bodies, which are known as chromosomes. In the prokaryotic cell, the chromosome formation is not present.
The eukaryotic cells always have two or more than two chromosomes in a single cell, whereas the prokaryotic cell has just one chromosome in a single cell.
Every eukaryotic chromosome contains a linear DNA having two ends, whereas a prokaryotic chromosome possesses a circular DNA that is covalently closed.
The eukaryotic chromosomes are separated from the cytoplasm by the nuclear membrane, whereas the prokaryotic chromosomes do not have a nucleus and are directly in contact with the cytoplasm.
Basically, the prokaryotic chromosome is a primitive type of chromosome, whereas the eukaryotic chromosome is an advanced type.
Comparison between Chromosomes and Chromatin
Chromosomes can be defined as the thread-like or rod-like structures which are found in the cellular living organisms which contain the genetic material deoxyribonucleic acid or DNA. The DNA plays an important part in heredity as the characteristics of each reproducing parent is passed down to the offspring. In eukaryotes, the chromosomes are present in the nucleus whereas in the prokaryotes there is only a ring-shaped chromosome called the genophore. The chromosomes carry the genes which have hereditary information and give the organism its characteristics. A single chromosome has two homogeneous or similar structures that are held together at a certain point called the centromere. The structures are called the chromatids which means one chromosome has 2 chromatids that are connected by the centromere. The chromosome appears like the alphabet X. Cytogenetics is the study of chromosomes as well as cell division.
The chromosomes and chromatids differ from each other and their differences are given as below:
Chromosomes have the genetic material DNA whereas chromatids help the cells in cell division and their duplication.
The chromosomes are present throughout the whole cell life cycle but chromatids are formed when the cell has to undergo cell divisions.
Chromosomes are not the copies of each other but the sister chromatids present in the chromosomes are copies of each other and are identical.
Chromosomes have centromeres to which the chromatids are attached and the sister chromatids have centromeres only.
In chromosomes, DNA is used for the synthesis of macromolecules like proteins but it is not used by chromatids.
Conclusion
Vedantu experts have covered all the major aspects of the difference between Chromosome and Chromatid.
FAQs on Chromosome vs Chromatid: What Sets Them Apart?
1. What is the main difference between a chromosome and a chromatid?
The primary difference lies in their structure and timing within the cell cycle. A chromosome is a single, condensed molecule of DNA that carries genetic information. A chromatid, specifically a sister chromatid, is one of two identical copies of a chromosome that are formed after DNA replication. These two identical chromatids are joined together at a region called the centromere, forming a replicated chromosome, which is what we typically picture when we see a chromosome diagram.
2. What is the relationship between chromatin, chromatids, and chromosomes?
These three terms describe different levels of DNA packaging within a eukaryotic cell.
- Chromatin is the least condensed form, consisting of DNA wrapped around proteins (histones). This is the state of DNA during the cell's normal growth phase (interphase).
- When the cell prepares to divide, the chromatin supercoils and condenses tightly to form a visible chromosome.
- After the DNA is duplicated, this single chromosome consists of two identical sister chromatids joined at the centromere.
3. When can you see distinct chromosomes and chromatids inside a cell?
You can only see these structures at specific stages of the cell cycle. During interphase (the cell's growth period), DNA exists as diffuse chromatin and is not visible as distinct structures. Distinct, condensed chromosomes, each composed of two sister chromatids, become visible during prophase and are most clearly seen during metaphase. The sister chromatids separate during anaphase, and from that point on, each is considered an individual chromosome.
4. How do sister chromatids differ from homologous chromosomes?
This is a common point of confusion. The key difference is their origin and genetic content.
- Sister Chromatids are two identical copies of a single chromosome, created during DNA replication. They are genetically identical and joined by a centromere until they separate in mitosis or meiosis II.
- Homologous Chromosomes are a pair of chromosomes, one inherited from each parent. They are the same size and contain the same genes in the same order, but they may carry different versions (alleles) of those genes. They pair up during meiosis I but are not physically joined like sister chromatids.
5. What is the specific function of a centromere?
The centromere is a constricted region on a chromosome that serves two critical functions during cell division. Firstly, it holds the two sister chromatids together after DNA replication. Secondly, it is the site where the kinetochore forms, a protein complex to which the spindle fibres attach. This attachment is essential for pulling the chromatids apart and ensuring each new daughter cell receives one copy of the chromosome.
6. Why is the correct structure of chromosomes so important for living things?
The precise structure and number of chromosomes are vital for life because they ensure the faithful transmission of genetic information from one generation of cells to the next. Chromosomes allow the massive amount of DNA to be managed, copied, and distributed evenly during cell division (mitosis and meiosis). Any errors in this process, such as a change in chromosome number (e.g., aneuploidy) or structure (e.g., deletion, translocation), can lead to severe genetic disorders like Down's syndrome, Turner's syndrome, or various types of cancer.
7. Do chromosomes split into chromatids during cell division?
No, the process is the reverse. A replicated chromosome, which already consists of two sister chromatids, is what enters the main phases of cell division. During a key stage called anaphase, the proteins holding the sister chromatids together dissolve, and the spindle fibres pull these chromatids to opposite poles of the cell. Once the sister chromatids separate, each one is reclassified as a complete, individual chromosome.
8. What are the key examples of differences between prokaryotic and eukaryotic chromosomes?
While both carry genetic material, prokaryotic and eukaryotic chromosomes have fundamental differences:
- Structure: Eukaryotic chromosomes are linear, while prokaryotic chromosomes are typically circular.
- Location: Eukaryotic chromosomes are contained within a membrane-bound nucleus. Prokaryotic chromosomes are located in the cytoplasm in a region called the nucleoid.
- Number: Eukaryotic cells have multiple chromosomes (e.g., humans have 46). Prokaryotic cells usually have just a single chromosome.
- Proteins: Eukaryotic DNA is tightly coiled around proteins called histones. Prokaryotic DNA is associated with histone-like proteins but is less structured.
