Abstract
The supernumerary B chromosome of maize has a drive mechanism to maintain itself in a population despite being dispensible. This involves nondisjunction of the B centromere at the second pollen mitosis that produces the two sperm followed by preferential fertilization of the egg by the B containing sperm during double fertilization. During an introgression of the supernumerary B chromosome into the inbred line B73, an unusually high frequency of trisomies for A chromosomes was observed. Due to parallels to the High Loss phenomenon in which three or more B chromosomes in a specific genetic background cause chromosomal breakage at heterochromatic knob sites during the second pollen mitosis as well as ploidy changes, this phenomenon was revisited. Examination of pollen of the High Loss line revealed a high frequency of single sperm in the presence of the B chromosomes, which was previously not realized. Crosses to tetraploid females confirmed that the single sperm were diploid and functional but also revealed the presence of diploids with their A chromosomes derived solely from the tetraploid parent indicating a "diploid induction". Collectively, the results reveal two backgrounds in which the B drive mechanism is not confined to this chromosome causing detrimental effects by adherence of heterochromatic knobs and apparently A centromeres at the mitosis preceding sperm development. In most genetic backgrounds this process is restricted to the B chromosome but in B73 and the High Loss line, there is spillover to the normal chromosomes in distinct ways.
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Claims 6
Claim · model-written summary
Pollen of the High Loss line showed a high frequency of single sperm in the presence of B chromosomes
- Material
- High Loss linee1
- Organ / stage
- pollene1
- Treatment
- presence of the B chromosomese1
- Outcome
- a high frequency of single sperme1
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize”
e1“Examination of pollen of the High Loss line revealed a high frequency of single sperm in the presence of the B chromosomes”
Claim · model-written summary
The single sperm produced by crosses were diploid and functional
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize”
e2“Crosses to tetraploid females confirmed that the single sperm were diploid and functional”
Claim · model-written summary
Some diploids had their A chromosomes derived solely from the tetraploid parent, indicating diploid induction
- Outcome
- presence of diploids with their A chromosomes derived solely from the tetraploid parente3
- Qualifier
- diploid inductione3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize”
e3“revealed the presence of diploids with their A chromosomes derived solely from the tetraploid parent indicating a "diploid induction"”
Claim · model-written summary
Introgression of the B chromosome into inbred line B73 yielded an unusually high frequency of A chromosome trisomies
- Material
- inbred line B73e4
- Treatment
- introgression of the supernumerary B chromosomee4
- Outcome
- frequency of trisomies for A chromosomese4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize”
e4“During an introgression of the supernumerary B chromosome into the inbred line B73, an unusually high frequency of trisomies for A chromosomes was observed”
Claim · model-written summary
The B drive mechanism causes detrimental effects through adherence of heterochromatic knobs and A centromeres at the mitosis preceding sperm development
- Outcome
- detrimental effectse5
- Qualifier
- adherence of heterochromatic knobs and apparently A centromeres at the mitosis preceding sperm developmente5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize”
e5“Collectively, the results reveal two backgrounds in which the B drive mechanism is not confined to this chromosome causing detrimental effects by adherence of heterochromatic knobs and apparently A centromeres at the mitosis preceding sperm development”
Claim · model-written summary
In B73 and the High Loss line, the B drive spilled over to normal chromosomes
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize”
e6“In most genetic backgrounds this process is restricted to the B chromosome but in B73 and the High Loss line, there is spillover to the normal chromosomes in distinct ways”