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WHY LINEAR #2. "Even crossing over between one linear and one circular chromosome will yield a linear dicentric that would also be unstable. The advent of sexual crosses may well have driven the advent of the linear chromosome: An ancestral protoeukaryote might have had two circular chromosomes with centromeres; their recombination would have yielded a circular dicentric that, when subjected to incomplete breakage-fusion-reunion cycles, could have given rise to linear chromosomes." https://lnkd.in/ebVhXPf View in LinkedIn

REPETITIVE ELEMENT PLAGUE. "The Group II introns residing in the genome of the ingested future mitochondrion are proposed to have colonized the host genome resulting in a large number of repetitive elements." https://lnkd.in/d8Qr_bk View in LinkedIn

WHY LINEAR #1. "The earliest protoeukaryotes may have had only one or a few linear chromosomes encompassing the entire genome (which also necessitated the evolution of centromeres and telomeres to allow faithful segregation and protect the ends from decay). Linear chromosomes are required because crossing over between two circular chromosomes generates a circular dicentric that is unstable (the chromosome is broken if the two centromeres attach to opposite spindle microtubules)." http://cshperspectives.cshlp.org/content/6/3/a016154.full View in LinkedIn

GROUP II INTRONS. "They can also spread through the genome by a similar, but less efficient reaction at ectopic sites. The phagocytosis of an α-proteobacterial cell by archaeal (or actinobacterial) eukaryotic precursor could have been accompanied by massive invasion of Group II introns." https://lnkd.in/d8Qr_bk View in LinkedIn

WHY LINEAR CHROMOSOMES? "There are several reasons to suggest that protoeukaryotes had linear chromosomes, or at least that these arose when meiosis evolved." https://lnkd.in/ebVhXPf View in LinkedIn

ANCESTRAL RETROTRANSPOSONS. "I propose that mobile Group II self-splicing elements (Group II introns) are a good candidate for the repeats that led to chromosome linearization. Group II introns are the proposed ancestors of introns and non-LTR retrotransposons." https://lnkd.in/d8Qr_bk View in LinkedIn

INFREQUENT EXAMPLES. "As logical as genomic streamlining might be, few examples have so far been found. Instead, a bevy of articles from the last 10 years show that three separate lines of evidence argue against widespread streamlining in prokaryotes." https://lnkd.in/d3Ys7Am View in LinkedIn

GENOMIC STREAMLINING. "Genomic researchers have proposed that natural selection may favor small genomes—weeding out superfluous material—through a process called “genomic streamlining.” Streamlining makes inherent sense because a small genome should aid metabolic efficiency, because genome size is correlated with cell size." https://lnkd.in/d3Ys7Am View in LinkedIn

GENOME DOWNSIZING. "Evolutionary chromosome change involves significant variation in DNA amount in diploids and genome downsizing in polyploids." https://lnkd.in/dmkwGfy View in LinkedIn

SIMPLICITY NOT SELECTED. "In part, the answer must be that most processes in eukaryotes generally evolve toward complexity, presumably because complexity provides more regulatory opportunities and perhaps also because there is no selective pressure to enforce simplicity." Not always true. https://lnkd.in/d8Qr_bk View in LinkedIn