Accessory chromosome

Accessory Chromosome

An accessory chromosome, also known as a B chromosome or supernumerary chromosome, is a chromosome that is not essential for the survival or reproduction of an organism, but may provide some selective advantage. These chromosomes are additional to the normal set of chromosomes, or A chromosomes, and are found in a variety of organisms, including plants, animals, and fungi.

Characteristics

Accessory chromosomes are typically smaller than A chromosomes and do not pair with any chromosome during meiosis. They are often rich in repetitive DNA sequences and lack genes that are vital for survival. However, they may contain genes that confer some sort of advantage to the organism, such as resistance to disease or increased fertility.

Distribution and Function

Accessory chromosomes are found in a wide range of organisms, from plants and animals to fungi. In plants, they have been observed in species such as maize and rye, while in animals, they have been found in insects like grasshoppers and beetles. In fungi, accessory chromosomes can carry genes for toxin production or resistance to fungicides.

The function of accessory chromosomes is not well understood, but it is thought that they may play a role in adaptation to changing environments. For example, in the fungus Fusarium oxysporum, accessory chromosomes carry genes that allow the fungus to infect different host plants.

Evolution

The origin and evolution of accessory chromosomes is a topic of ongoing research. It is thought that they may arise from A chromosomes through processes such as chromosome breakage or duplication. Over time, these extra chromosomes may accumulate beneficial mutations and become established in a population.

See also

• Chromosome
• Meiosis
• Fusarium oxysporum