Linkage
As the name implies, linkage means the carrier of a gene or trait that is attached to a chromosome, that is, a gene or group of genes that are located on a chromosome and are inherited along with the chromosome in the next generation, linked genes or linked genes. These linked genes are never isolated. These genes remain attached to the chromosome even after meiosis and are inherited in the next generation and this process is called linkage. The term linkage was first used by Sutton and Boveri. Used by various researchers to explain linkage. Some cases were presented on the basis of which the brief details are as follows –
- Experiment of Bateson and Punnett: Bateson and Punnett demonstrated linkage in a plant named Lathyrus Odoratus. Using dihybrid hybridization, they crossed homozygous plant with blue and long pollen grains with a homozygous plant with red and round pollen grains. After crossing the first generation (F 1), according to the first law of Mendel, the symptoms of the rule of dominant appeared. On crossing the F 1 generation with a parent with recessive traits, that is, on conducting a Test Cross, this general rule in the second generation This means that the genes did not separate from each other at the time of dihybrid hybridization, and we got plants with different characters.
- Morgan's Theory or Morgan's Chromosomal Theory of Linkage : According to Morgan, "due to the presence of genes on the same chromosome, the genes remain in their original form and are inherited in the next generation at the time of inheritance. The smaller the distance between the linked genes." Will be, the higher will be their tendency to be hereditary. As the distance increases, the tendency of their inheritance will decrease.
- Morgan did his experiment on Drosophila fly. In this, for dihybrid hybridization, he hybridized a fly with normal color and wings with a fly with black color and vestigial wings, then hybridized a hybrid plant with dominant traits obtained in the first generation (F 1) with an ineffective conjugation test hybridization – test cross. If done, flies with only two characters were obtained in the F 2 generation. Thus, contrary to the rules, the receipt of only two characters, shows the linkage of genes to chromosomes.
Type Of Linkage
- Incomplete Linkage
- Complete Linkage
1. Incomplete Linkage
In homologous chromosomes, due to breakage of chromosomes at the time of gene exchange or crossing over, linked genes are separated and new combinations are obtained as a result of exchange of chromosomes, then the offspring of the next generation get the characteristics of the parent type and the recombined type. are | This process is called incomplete linkage. In incomplete linkage, genes located on different chromosomes are inherited independently and may also meet at the time of crossing over during gametogenesis.
2. Complete Linkage
When the linked genes on the homologous chromosome do not separate during the crossing over that occurs during meiosis, and show the parental type in the next generation, the process is called complete linkage. All genes located on a chromosome are inherited together.
Importance Of Linkage
Mainly two things are clear from linkage –
- In the offspring of the next generation, the ancestral qualities or traits are received from their descendants.
- Without crossing over diversity is not possible in the next generation or we can say that without crossing over new traits will not appear.
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