Question

Describe the following errors of meiotic recombination: A) Unequal crossing over B) Exon shuffling

Answer 1

Description

A) unequal crossing over:

It is a type of gene duplication or deletion event during meiotic recombination that deletes a sequence in one strand and replaces it with a duplication from its sister chromatid either from mitosis or from its homologous chromosomes from meiosis.

It exchanges sequences of different links between chromosomes.

Mechanism of unequal crossing over:

During meiosis, the duplicated chromosomes (chromatids) in eukaryotic organisms are attached to each other in the centromere region and are thus paired. The maternal and paternal chromosomes then align alongside each other. During this time, recombination can take place via crossing over of sections of the paternal and maternal chromatids and leads to reciprocal recombination or non-reciprocal recombination. Unequal crossing over requires a measure of similarity between the sequences for misalignment to occur. The more similarity within the sequences, the more likely unequal crossing over will occur. One of the sequences is thus lost and replaced with the duplication of another sequence.

Initial duplication of single copy region Further expansion from a two repeat cluster B' B с B genetic exchange sites B 10 A' B region of pairing B с Crossover site B' B/B B reciprocal products deleted chromosome C divergence A A B1 B2 B3 A ere с B B duplicated segments three-member gene family cluster

B) Exon shuffling:

It is a usual molecular mechanism for the formation of new genes. It is a process through which two or more exons from different genes can be paired together ectopically or the same Exon can be duplicated to create a new exon-intron structure.

Exon shuffling requires the creation of DNA fragments containing exons or combinations of exons that encode a protein domain.

Mechanism:

There is a mechanism of Exon shuffling for the formation and shuffling of said domains, this is the modularization hypothesis. This mechanism is divided into three stages. The first stage is the insertion of introns at positions that correspond to the boundaries of a protein domain. The second stage is when the "protomodule" undergoes tandem duplications by recombination within the inserted introns. The third stage is when one or more protomodules are transferred to a different nonhomologous gene by intronic recombination. All states of modularization have been observed in different domains such as those of hemostatic proteins.

EXON SUFFLING SWITCH RECOMBINATION

Please upvote