Genetic Linkage

The tendency of genes on a chromosome to stick together during chromosomal inheritance is known as linkage. Contrarily, crossing over is the process through which genetic material from homologous chromosomes is exchanged to create a new gene combination. Linkage creates parental types and aids in the preservation of a better new variety.

Significance of Linkage

1. For upcoming generations, it helps in restoring the paternal genes
2. It’s important to preserve a newly developed variety’s positive trait
3. It is essential for determining a plant’s capacity for hybridization.

Genetic Linkage

In the meiosis stage of sexual reproduction, DNA sequences that are near to one another on a chromosome tend to be inherited together. Physical proximity between two genetic markers makes it less probable that they would split into separate chromatids during the chromosomal crossover, and as a result, they are said to be more related than markers that are physically far apart. In other words, the likelihood that two genes will be inherited jointly increases with increasing proximity between them on a chromosome.

Although there is no connection between markers on different chromosomes, the penetrance of potentially harmful alleles may be influenced by the presence of other alleles, and these other alleles may be found on different chromosomes than the one on which a particular potentially harmful allele is located.

History of Genetic Linkage

Soon after Mendel’s rules were rediscovered, the British geneticists William Bateson and Reginald Punnett made the first discovery of genetic linkage. Thomas Hunt Morgan’s research contributed to a greater knowledge of genetic linkage. The idea that crossover frequency might represent the distance separating genes on the chromosome was inspired by Morgan’s finding that the amount of crossing over between connected genes varies.

Example of Genetic Linkage

ABO Blood Groups with Nail-Patella Syndrome

The nail-patella syndrome, sometimes called hereditary onychosteodysplasia, is a collection of flaws. From a triangular lunule to a mild abnormality with discoloration, a longitudinal fracture, and reduced size, to severe dystrophy with the removal of a sizable piece of the nail, there are various types of nail dystrophy. The thumb, index finger, and first and second toes are most affected. The patellae are frequently basic or nonexistent. Some of the affected patients have strange conical bony growths called “iliac horns” that protrude from the center of the iliac bone. Additionally, elbows frequently display abnormalities.

There are numerous defects in this way, but they are not very serious, and it does not appear that life expectancy or fertility is affected. The nail-patella syndrome’s dominant gene demonstrates great regularity of transmission. Affected people always have one affected parent, and an affected X will typically produce an equal number of affected and normal kids when they mate. This is known as the perfect regularity of transmission.

A pedigree examination of nine family groups revealed that the ABO gene locus and the nail-patella gene locus share a chromosome and are separated by around 10 units of crossing over. It’s crucial to remember that the nail-patella gene is unrelated to any one specific ABO gene.
In some families, it is on a chromosome that is home to the B gene, in other families, it is on a chromosome that is home to the O gene, and in extremely uncommon cases, it is to the A gene. When examining the blood groups of affected parents’ offspring from different pedigrees, the distribution between those with nail-patella syndrome and those without it is as follows:

	Blood groups				Total
	O	A	B	AB
Affected with (Nail patella)	62	53	20	4	139
Normal	62	79	13	6	160

Clinical Application of Genetic Linkage

1. Enables the discovery of marker genes connected to severe dominant diseases.
2. Genetic linkage improves the prediction of the disease’s distribution in short-family pedigrees.
3. A genetic marker would typically be a collection of alleles at a locus that is tightly linked to the specific illness gene; the closer the link, the better the marker because there is less uncertainty caused by potential gene crossover between the marker and disease genes.
4. Genetic linkage does not mean that a particular allele is connected to the disease in general.

FAQs on Genetic Linkage

Question 1: Define Linkage. Mention the name of types of Linkage.

Answer:

Linkage is the ability of genes on a chromosome to remain together throughout chromosomal inheritance. On the other hand, crossing over is a process where genetic material from homologous chromosomes is transferred to produce a new gene combination.
Types of linkage:

• Complete linkage
• Incomplete linkage

Question 2: Who discovered the first about genetic linkage?

Answer:

The first genetic linkage discovery was made by British geneticists William Bateson and Reginald Punnett.

Question 3: What is linkage analysis?

Answer:

In order to identify chromosomal regions that regularly correlate with a certain phenotype over the course of a family’s generations, linkage analysis is utilized. Linkage analysis can be used to find the linkage maps of both binary and quantitative features.

Question 4: Write any two clinical applications of genetic linkage.

Answer:

1. Genetic connection enhances short family pedigree illness spread prediction.
2. Genetic linkage does not necessarily indicate that a certain allele is linked to the disease generally.

Question 5: Write briefly about recombination frequency.

Answer:

A genetic linkage map is created using recombination frequency, a genetic relationship indicator. The recombination frequency (θ) is the frequency of a single chromosomal crossover taking place between two genes during meiosis.