X-monosomy in the Indian black rat

Area of Science:

• * Cytogenetics
• * Mammalian genetics
• * Zoology

Background:

• * The south Indian black rat, Rattus r. rufescens, is a significant rodent species in its native range.
• * Standard diploid chromosome number in Rattus species is typically 38.
• * Understanding chromosomal variations is crucial for evolutionary and genetic studies.

Purpose of the Study:

• * To investigate chromosomal abnormalities in a population of Rattus r. rufescens from Mysore, India.
• * To characterize aneuploidies, including XO conditions and supernumerary chromosomes.
• * To discuss the implications of these chromosomal variations in mammals.

Main Methods:

• * Karyotypic analysis of random samples of Rattus r. rufescens.
• * Microscopic examination of chromosomes to determine diploid numbers and identify abnormalities.
• * Comparison of observed karyotypes with the standard diploid number.

Main Results:

• * Aneuploid chromosome numbers (2n = 37, 39, 40, 42) were observed in the sampled population.
• * A female individual with a 37-chromosome count and an XO constitution was identified.
• * Chromosome numbers exceeding the diploid count of 38 were attributed to the presence of supernumerary (B) chromosomes.

Conclusions:

• * The study documents significant chromosomal variations within the Rattus r. rufescens population.
• * The identified XO condition in a female rat provides data on sex chromosome abnormalities in this species.
• * The presence of B chromosomes suggests potential mechanisms for genetic diversity and adaptation in Rattus r. rufescens.