Recombination vs. Crossing Over
Recombination and Crossing Over Definitions
Recombination vs. Crossing Over
Recombination generally refers to the formation of offspring that consist of many diverse or different combinations of traits; on the other hand, crossing over is usually refers to the interchange of genetic material like DNA segments among the non-sister chromatids. In recombination, crossing over is the reason which leads to genetic recombination of chromosomes; on the contrary, in crossing over, synapsis results in crossing over. Recombination always occurs in individuals and transfer to the next generation; on the other hand, crossing over may or may not always occurs in homologous chromosomes or if not occur, then only parental chromosomes will be observed.
Genetic recombination plays a vital role in genetic diversity in species or at the population level; on the contrary, crossing over employing genetic recombination allows variations at alleles of chromosomes in an offspring. In recombination, the two different alleles always combine during meiosis and transfer to the next generations; on the flip side, in crossing over, the segments of DNA in non-sister or homologous chromosomes are exchanged during this procedure. Recombination works as a renovation mechanism for double-strand breaks during the process of meiosis and forms genetic variations in offspring; on the other hand, crossing overplays a role in the exertion of the genetic recombination among homologous chromosomes.
What is Recombination?
The term recombination is defined as the formation of offspring having different arrangements of traits as an associate to the parent by the combination of different alleles in the chromosomes. Genetic recombination is considered as a natural process and always occurs during meiosis. The genetic recombination in eukaryotes happens in prophase 1 of meiosis 1. Meiosis is considered as the method of formation of different gametes for the process of sexual production. The formation of genetically varying offspring is the result of variation that occurs in genes of parent’s gametes during meiosis by the process of genetic recombination.
The pairing of homologous chromosomes which is followed by the interchange of genetic knowledge among the non-sister chromatids occurs in eukaryotic genetic recombination. The combination of non-sister chromatids is considered as synapsis. The interchange of DNA segments could happen through either non-physical transfer or physical transfer. The types of non-physical transfer are synthesis-dependent strand annealing (SDSA) or double Holliday junction (DHJ) that are started by a double-strand break or by a gap that follows through the attack of strands to initiate the copying of genetic material. Hence, both SDSA and DHJ pathways are deliberated as renovation mechanisms.
In the process of mitosis, the interchange of genetic information happens among the sister chromatids just after the replication of DNA is finished at the point of interphase. Though, new allele groupings are not formed in this process because the exchange of material happens among the identical DNA molecules that are formed by the replication method.
The catalyzes of genetic recombination is done by the class of enzymes known as recombinases. The RecA recombinase is commonly found in bacteria E. coli. In this type of bacteria, the recombination happens through the process of mitosis, and the transmission of genetic material by sister chromatids occurs between their organism. In the type of bacteria, archaea, the recombinase enzyme RadA is found that is considered as an orthologous of RecA. Another recombinase RAD51 id found in yeast. A particular meiotic recombinase found is DMC1.
Types of Recombinase Enzyme
- RecA: Found in E. coli
- RadA: Found in archaea as orthologous of RecA
- RAD51: Found in yeast
- DMC1: Found as a particular meiotic recombinase
Ways of Transferring of Genetic Information
- Physical Transfer: The transfer of genetic information which happens by the interchange of chromosomal segments among non-sister chromatids is generally the physical transfer.
- Non-physical Transfer: The method in which sections of one genetic material that are present in one chromosome could be copied into another segment of chromosome without physically having the exchange of chromosomal parts is known as a non-physical transfer.
Types of Non-Physical Transfer
- Synthesis-Dependent Strand Annealing (SDSA): In this type of non-physical transfer, the copying of genetic material happens in which it permits the interchange of materials but not through the physical interchange of DNA segments.
- Double Holliday Junction (DHJ): This is another copying of the genetic information that results in the non-physical transmission of genetic material.
Types of Copying of Information
- Non-Crossover (NCO): In this type, when a renovation of a broken strand happens, then only the one chromosome that embraces the double-strand break is transmitted with the new information.
- Crossover (CO): In this type, both of the chromosomes that hold the double beak strand or others which do not hold are transmitted with novel genetic material.
What is Crossing Over?
The term crossing over is defined as the interchange of parts of DNA among the non-sister chromatids during the process of synapsis. The process of crossing over happens in the prophase 2 of meiosis 1. Crossing over usually facilitates the genetic recombination by interchanging the genetic material between two homologous chromosomes and forming a new mixture of alleles.
The process of crossing is started by the dissociation of the same DNA segments that happen in the pairs of the homologous chromosomes. The DNA molecule is introduced through the double-strand breaks either by DNA damaging agents or by Spo 11 protein. After this, the 5’ end of the DNA corners is decomposed by exonucleases. The digestion of 5’ end introduces the 3’ which extends into the edges of DNA of double-stranded DNA.
The extended single-stranded 3’ is coated by recombinases that form nucleoprotein filaments, Rad51 and Dmc 1. The speedup of occupied 3’ extension into the non-sister chromatids is by recombinases. The entered 3’ extension primes the synthesis of DNA by using the DNA strand of non-sister chromatids as a template. The leading structure of this invaded 3’ in called as cross-strand interchange or the Holliday junction. The recombinase dragged the Holliday junction along the chiasma.