Thursday, March 28, 2024
General Agriculture

Types and Consequences of Inversion

Inversion occurs if two breaks occur in one chromosome, sometimes the region between the breaks rotates 180 degrees before rejoining with the two end fragments. Such an event creates a chromosomal mutation called an inversion.

Unlike deletions and duplications, inversions do not change the overall amount of the genetic material, so inversions are generally viable and show no particular abnormalities at the phenotypic level.

In some cases, one of the chromosome breaks is within a gene of essential function, and then that breakpoint acts as a lethal gene mutation linked to the inversion. In such a case, the inversion could not be bred to homozygousity. However, many inversions can be made homozygous; furthermore, inversions can be detected in haploid organisms.

Types and Consequences of Inversion

Most analyses of inversions use heterozygous inversions – diploids in which one chromosome has the standard sequence and one carries the inversion.

Microscopic observation of meioses in inversion heterozygotes reveals the location of the inverted segment because one chromosome twists once at the ends of the inversion to pair with the other, untwisted chromosome; in this way the paired homologs form an inversionloop(Figure).

The location of the centromere relative to the inverted segment determines the genetic behavior of the chromosome. If the centromere is outside the inversion, then the inversion is said to be paracentric, whereas inversions spaning the centromere are pericentric:

How do inversion behave genetically? Crossing-over within the inversion loop of a paracentric inversion connects homologous centromeres in a dicentric bridgewhile also producing an acentric fragment– a fragment without a centromere.

Then, as the chromosomes separate in anaphaseI, the centromeres remain linked by the bridge, which orients the centromeres so that the noncrossover chromatids lie farthest apart. The acentric fragment cannot align itself or move and is, consequently, lost.

Tension eventually breaks the bridge, forming two chromosomes with terminal deletions (Figure.). The gametes containing such deleted chromosomes may be inviable but, even if viable, the zygotes that they eventually form are inviable.

Hence, a crossover event, which normally generates the recombinant class of meiotic products, instead produces lethal products. The overall result is a lower recombinant frequency. In fact, for genes within the inversion, the RF is zero. For genes flanking the inversion, the RF is reduced in proportion to the relative size of the inversion.

Inversions affect recombination in another way too. Inversion heterozygotes often have mechanical pairing problems in the region of the inversion; these pairing problems reduce the frequency of crossing-over and hence the recombinant frequency in the region.

The net genetic effect of a pericentric inversion is the same as that of a paracentric one – crossover products are not recovered – but for different reasons. In a pericentric inversion, because the centromeres are contained within the inverted region, the chromosomes that have crossed over disjoion in the normal fashion, without the creaton of a bridge.

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However, the crossover produces chromatids that contain a duplication and a deficiency for different parts of the chromosome. In this case, if a nucleus carrying a crossover chromosome is fertilized, the zygote dies because of its genetic imbaolnace.

Again, the result is the selective recovery of noncrossover chromosomes in viable progeny. Thus, inversions are referred to as crossover suppressors because crossover products of inversion are not recovered.

Synaps is in Paracentric In version Heterozygote

Inversion

In conclusion, the mechanisms reduce the number of recombinant product among the progeny of inversion heterozygote: elimination of the products of crossovers in the inversion loop and inhibition of pairing in the region of the inversion.

Inversion occurs when two breaks in a chromosome is followed by a 1800 rotation and rejoining of the inverted segment.

The main diagnostic features of inversions are inversion loops, reduction of recombinant frequency, and reduced fertility from unbalanced or deleted meiotic products characteristic of inversion heterozygotes.

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Agric4Profits

Benadine Nonye is an agricultural consultant and a writer with over 12 years of professional experience in the agriculture industry. - National Diploma in Agricultural Technology - Bachelor's Degree in Agricultural Science - Master's Degree in Science Education... Visit My Websites On: 1. Agric4Profits.com - Your Comprehensive Practical Agricultural Knowledge and Farmer’s Guide Website! 2. WealthinWastes.com - For Effective Environmental Management through Proper Waste Management and Recycling Practices! Join Me On: Twitter: @benadinenonye - Instagram: benadinenonye - LinkedIn: benadinenonye - YouTube: Agric4Profits TV and WealthInWastes TV - Pinterest: BenadineNonye4u - Facebook: BenadineNonye

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