B CHROMOSOMES IN ANGIOSPERM--A REVIEW.

Area of Science:

• Plant genetics
• Evolutionary biology
• Cytogenetics

Background:

• B chromosomes (Bs) are accessory chromosomes found in various organisms, including angiosperms.
• Their origin, evolution, and precise role in host plant genomes remain incompletely understood.
• Previous research has identified Bs in numerous plant species, highlighting their diverse morphology and behavior.

Purpose of the Study:

• To provide a comprehensive review of B chromosomes in angiosperms.
• To explore the occurrence, morphology, and genetic characteristics of Bs.
• To discuss the evolutionary aspects and host interactions of B chromosomes, aiming to clarify their enigmatic nature.

Main Methods:

• Literature review of existing studies on B chromosomes in angiosperms.
• Analysis of data on B chromosome occurrence, morphology, and genetic content.
• Synthesis of information regarding B chromosome origin, evolution, and function.

Main Results:

• B chromosomes exhibit significant diversity in occurrence, morphology, and polymorphic forms across angiosperm species.
• They possess unique features like divisional phase heterogeneity, altered chromatin organization, and specific sequence compositions.
• Bs demonstrate modifications such as centromeric/telomeric sequence insertion, structural reorganization, and acquisition of mitotic/meiotic drives.
• Despite these modifications, Bs generally function as genetically inert, selfish DNA within the host genome.

Conclusions:

• B chromosomes represent a fascinating area of evolutionary genetics in angiosperms.
• Their complex modifications and selfish nature suggest unique evolutionary trajectories.
• Further research is needed to fully unravel the evolutionary significance and mechanisms of B chromosomes.