An extrachromosomal factor causing loss of paternal chromosomes

Area of Science:

• Genetics
• Evolutionary Biology
• Reproductive Biology

Background:

• Extrachromosomal inheritance is typically maternal in animals, unlike chloroplasts and mitochondria.
• Paternal inheritance exceptions are rare, with the sex ratio factor (psr) in Nasonia vitripennis being a known case.
• The psr factor leads to all-male offspring, challenging typical inheritance patterns.

Purpose of the Study:

• To elucidate the mechanism of paternal transmission of the sex ratio factor (psr) in Nasonia vitripennis.
• To investigate how the psr factor leads to all-male offspring despite fertilization.

Main Methods:

• Microscopic observation of fertilized eggs from psr-infected males.
• Analysis of paternal chromosome behavior post-fertilization.

Main Results:

• Sperm from psr males successfully fertilize eggs.
• Paternal chromosomes condense into a chromatin mass before the first mitotic division.
• Condensed paternal chromosomes are excluded from further cell division, resulting in haploid, male offspring.

Conclusions:

• The psr factor is transmitted via sperm but prevents paternal chromosome incorporation.
• This mechanism ensures the transmission of the extrachromosomal factor at the expense of paternal genetic contribution.
• The psr factor acts as a selfish genetic element promoting its own propagation.