The behavior during pachynema of a normal and an inverted Y chromosome in Microtus agrestis

Area of Science:

• Cytogenetics
• Mammalian Genetics
• Reproductive Biology

Background:

• The X and Y chromosomes in mammals typically undergo synapsis (pairing) during meiosis to facilitate genetic exchange (crossing over).
• Variations in Y chromosome structure, such as inversions, can potentially impact meiotic behavior and fertility.
• Microtus agrestis (the field vole) presents a unique system for studying sex chromosome behavior due to its distinct Y chromosome morphology.

Purpose of the Study:

• To investigate the pachytene chromosome behavior in Microtus agrestis males with either a standard or a pericentrically inverted Lund Y chromosome.
• To determine if synapsis occurs between the X and Y chromosomes under these conditions.
• To assess the implications for crossing over and chiasma formation between the X and Y chromosomes.

Main Methods:

• Electron microscopy was used to examine microspread spermatocytes during the pachytene stage of meiosis.
• Analysis focused on the pairing interactions between the X and Y chromosomes.
• G-banding, C-banding, and NOR-banding techniques were applied to mitotic karyotypes for detailed chromosome characterization.

Main Results:

• No synapsis was observed between the X chromosome and either the standard or the inverted Lund Y chromosome throughout pachynema.
• The lack of synapsis suggests a complete absence of opportunity for crossing over or chiasma formation between the X and Y chromosomes in this species.
• Mitotic karyotypes revealed distinct banding patterns for both standard and inverted Lund Y chromosomes.

Conclusions:

• The X and Y chromosomes in Microtus agrestis do not engage in synapsis during male meiosis.
• This lack of pairing effectively prevents genetic recombination between the X and Y chromosomes in this rodent species.
• The findings contribute to understanding sex chromosome evolution and the mechanisms underlying male fertility in rodents.