Microchromosomes are a type of very small chromosome that is a typical part of the karyotype of some reptiles, birds, amphibians and fish. They are not normally found in mammals. It is less than 20 MB in size. Chromosomes larger than 40 MB are known as microchromosomes, and chromosomes between 20 and 40 MB are classified as intermediate chromosomes. Microchromosomes are usually very small and often indistinguishable cytogenetically in their karyotype. Chromosome length is generally measured in kb, bp, gb, Mb. Bp means base pair which is 1 bp = 643 or 618 daltons. Dalton is the basic measure of chromosomes. 1 MB = 1,000,000 bp, 1 kb = 1,000 bp and 1 GB = 1 billion bp.
Highlights
Originally thought to be unimportant chromosomal fragments, the species in which they were studied were found to be gene-rich and high in GC. In chickens, microchromosomes are estimated to contain 50-75% of all genes. The presence of microchromosomes makes chromosomal ordering and identification into coherent karyotypes particularly difficult. During the mid-term, they only appear as spots 0.51.5 m in length. Their small size and inadequate condensation into heterochromatin mean that they generally lack the diagnostic band patterns and unique centromere positions used for chromosome identification. When found, ?Chrs interact closely with each other and are well conserved. The genome composition of Florida Lancet, which is part of all vertebrate sister groups, depicts a possible ancestral genome of amniotes (and common vertebrates) made entirely of ?Chrs. Comparing the lancet and modern vertebrate chromosomes, we find that MChrs are the result of the fusion occurring between ?Chrs. In addition, retention of ?Chrs has been shown to be standard. Instead, it is outliers that mammals lose them altogether. Microchromosomes are very useful for the placement and identification of chromosomes.
Microchromosomes in Humans, Turtles and Birds
In birds, microchromosomes are abundant. Microchromosomes are used to determine the sex of turtles. There is no striking evidence that microchromosomes are found in humans. This is because chromosome 21 is the smallest chromosome in humans. This is 47MB. This means that all human chromosomes are macrochromosomes. However, there are certain facts related to human microchromosomes and Down’s syndrome.
Role of Microchromosomes in Mammals
In the month of November 2021, microchromosomes were found to play a larger role in mammals. Microchromosomes change with each new evolution in mammals. They are the main reason for the evolution of new mammals. They are components of vertebrates. Vertebrates are organisms that have a spine. We also found that the microchromosomes in the center of the nucleus gather to have functional coherence. That is, all microchromosomes in the cell work together.
