The main difference between chromosomal inheritance and extrachromosomal inheritance is that chromosomal inheritance refers to the transmission of genetic information through chromosomes located in the nucleus of the cell. In contrast, extrachromosomal inheritance refers to the transmission of genetic information through the structures outside of the chromosomes.
A chromosome is a DNA molecule that carries a part of the whole genetic information of an organism. This essential genetic information passes on to the next generation during reproduction. Chromosomal inheritance and extrachromosomal inheritance are two different mechanisms by which genetic material passes from one generation to the other.
Key Areas Covered
1. What is Chromosomal Inheritance
– Definition, Transmission of Genetic Information
2. What is Extrachromosomal Inheritance
– Definition, Transmission of Genetic Information
3. Difference Between Chromosomal and Extrachromosomal Inheritance
– Comparison of Key Differences
Key Terms
Chromosomal Inheritance, Cytoplasmic Inheritance, Extrachromosomal Inheritance
What is Chromosomal Inheritance
Chromosomal inheritance states that genes are located on chromosomes, and they are passed from the parent to the offspring. This theory is also known as the Sutton-Bovery theory. It is one of the fundamental concepts in genetics that explains how genetic information passes down from one generation to the next.
This theory supports Mendel’s laws. The observations related to chromosomal inheritance are as follows:
– Each parent produces gametes that contain only half of their chromosomal complement.
– A random distribution of chromosomes into pre-gametes from each homologous pair is seen.
– Female gamete and male gamete have the same number of chromosomes though they differ in size and morphology, submitting equal genetic contributions from each parent.
– Gametic chromosomes fuse during fertilization to produce offspring with the same number of chromosomes as their parents.
– During meiosis, a pair of homologous chromosomes move as discrete structures, which are independent of the other pairs of chromosomes.
The behaviour of chromosomes during meiosis explains the principle of segregation and the principle of independent assortment. These principles are a part of the chromosome theory of inheritance.
Down syndrome is an example of chromosomal inheritance caused by an extra copy of chromosome 21. Another example is Huntington’s disease; the cause of this disease is a mutation on chromosome 4, which leads to the progressive degradation of nerve cells in the brain,
Mutations can also cause chromosomal inheritance. These mutations can arise spontaneously or pass on from the parent.
What is Extrachromosomal Inheritance
Extrachromosomal inheritance (cytoplasmic inheritance) is a non-Mendelian pattern of inheritance governed by DNA in the cytoplasm. This basically refers to the transmission of genes that occur outside the nucleus. This is mostly present in eukaryotes. The inheritance of extra chromosomes is a frequent occurrence in cytoplasmic organelles such as mitochondria, plastids, and cellular parasites such as viruses and bacteria.
This was first reported by Boris Ephrusssi in yeast in 1949. There are a few criteria for extrachromosomal inheritance. They are as follows.
DNA does not follow the Mendelian pattern of inheritance, unlike the common nuclear DNA. The extrachromosomal DNA does not have its protein synthetic machinery for the process of replication, transportation, and translation. Hence, it synthesizes its own DNA and makes its own protein. As the female gamete contains more cytoplasm than male gametes, the extrachromosomal DNA is inherited from the maternal side. Moreover, all progenies of this type of inheritance have the phenotype of only one parent (which is the mother). But substituting the nucleus with a different genotype does not affect inheritance.
Examples of extrachromosomal inheritance are plastid inheritance in MIrabilis jalapa and cytoplasmic male sterility in maize.
Difference Between Chromosomal and Extrachromosomal Inheritance
Definition
Chromosomal inheritance states that genes are located on chromosomes, and they are passed from the parent to the offspring, while extrachromosomal inheritance is a non-Mendelian pattern of inheritance governed by the DNA in the cytoplasm.
Transmission of Genetic Information
While chromosomal inheritance involves the transmission of genetic information through chromosomes located in the nucleus of the cell, extrachromosomal inheritance involves the transmission of genetic information through the structures outside of the chromosomes.
Allowing Mendelian Patterns of Inheritance
Chromosomal inheritance follows the Mendelian pattern of inheritance, such as dominance, recessiveness, and segregation, whereas extrachromosomal inheritance is not always subject to these rules.
Amount of Genetic Material Transmitted
Chromosomal inheritance involves the transmission of large amounts of genetic material, whereas extrachromosomal inheritance involves the transmission of smaller amounts of genetic material.
Conclusion
In brief, chromosomal inheritance and extrachromosomal inheritance are two different mechanisms by which genetic material passes from one generation to the other. The main difference between chromosomal inheritance and extrachromosomal inheritance is that chromosomal inheritance refers to the transmission of genetic information through chromosomes located in the nucleus of the cell, whereas extrachromosomal inheritance refers to the transmission of genetic information through the structures outside of the chromosomes.
Reference:
1. “Extrachromosomal Inheritance: Definition, Criteria & Examples.” EMBIBE.
2. “Chromosomal Theory of Inheritance.” Byju’s.
Image Courtesy:
1. “Autorecessive en 01” By Kuebi = Armin Kübelbeck – own work, made with InkScape. PNG-File derived from SVG master (CC BY-SA 3.0) via Commons Wikimedia
Leave a Reply