Variation in Meiotic Recombination Frequencies Between Allelic Transgenes Inserted at Different Sites in theDrosophila melanogasterGenome

Abstract

Meiotic crossovers are distributed nonrandomly across the genome. Classic studies in Drosophila suggest that the position of a gene along a chromosome arm can affect the outcome of the recombination process, with proximity to the centromere being associated with lower crossing over. To examine this phenomenon molecularly, we developed an assay that measures meiotic crossovers and noncrossover gene conversions between allelic transgenes inserted into different genomic positions. To facilitate collecting a large number of virgin females, we developed a useful genetic system that kills males and undesired classes of females. We found that the recombination frequency at a site in the middle of the X chromosome, where crossovers are normally frequent, was similar to the frequency at the centromere-proximal end of the euchromatin, where crossovers are normally infrequent. In contrast, we recovered no recombinants—crossovers or noncrossovers—at a site on chromosome 4 and at a site toward the distal end of the X chromosome. These results suggest that local sequence or chromatin features have a stronger impact on recombination rates in this transgene assay than position along the chromosome arm.

The Drosophila Dot Chromosome: Where Genes Flourish Amidst Repeats

“…Since then, this lack of recombination for chromosome 4 in wild-type animals has been confirmed by several laboratories. For example, Sandler and Szauter examined ∼30,000 mitoses without finding evidence of recombination ( Sandler and Szauter 1978 ), and McMahan and colleagues investigated 1,285,000 progeny from a reporter assay and found no evidence of recombination at the 102D site ( McMahan et al 2013 ). More recently, Hatkevich and colleagues examined 3112 progeny for recombination between ci and sv on chromosome 4 without recovering any recombinants, while a parallel experiment looking for recombination in a stretch of pericentric heterochromatin on chromosome 2L revealed eight recombination events among 7399 animals ( Hartmann and Sekelsky 2017 ; Hatkevich et al 2017 ).…”

Comparative Cytology of Female Meiosis I AmongDrosophilaSpecies

“…In D. melanogaster the dot chromosome never undergoes recombination, with experimental samples in excess of one million progeny showing zero cases of homologous crossovers (McMahan et al 2013). This causes the dot chromosome to be frequently located out on the spindle during Prometaphase.…”

A drug-inducible sex-separation technique for insects

“…Finally, sex separation can also be achieved by negative selection against females using conditional sex-specific lethal transgenes that are repressed by continuous tetracycline feeding (a Tet-Off system), like in a few Tephritid fruit fies [21][22][23][24] and the yellow fever mosquito Aedes aegypti 25 , or activated by heat treatments, such as a temperature sensitive lethal (tsl) mutation in the Mediterranean fruit fly Ceratitis capitata (Medfly) [26][27][28] . In Drosophila, two Ylinked systems were used to remove males and generate virgins females: an inducible lethal (P{hs-hid}Y 29 ) and a Gal4-UAS transactivating lethal (P{UAS-rpr.Y} 30 ). The sex specificity of the marker expression and conditional lethal transgenes was generated serendipitously by linking it to a sex chromosome [25][26][27][29][30][31] , or by incorporation of a sex-specific promoter 25 , or a femalespecific intron into a coding sequence of a lethal transgene [21][22][23][24] .…”

“…In Drosophila, two Ylinked systems were used to remove males and generate virgins females: an inducible lethal (P{hs-hid}Y 29 ) and a Gal4-UAS transactivating lethal (P{UAS-rpr.Y} 30 ). The sex specificity of the marker expression and conditional lethal transgenes was generated serendipitously by linking it to a sex chromosome [25][26][27][29][30][31] , or by incorporation of a sex-specific promoter 25 , or a femalespecific intron into a coding sequence of a lethal transgene [21][22][23][24] .…”

“…The methods based on mechanical separation of different sexes are entirely species specific and cannot be adopted to others. In addition, they are not practical in most insects, since they require optimal rearing conditions, multiple transgenes, have a significant error rate, and are not suitable for high-throughput insect production 13,15,27,30,32 , with an exception of the Medfly 28 . Classic GSS approaches were achieved serendipitously in one species at a time, and thus are species specific.…”