Chromosome Bridge, Polyploidy and CD Darlington in Brenner’s Encyclopedia of Genetics

A Chromosome Bridge (arrow) at anaphase of mitosis in Tradescantia virginiana
A Chromosome Bridge (arrow) at anaphase of mitosis in Tradescantia virginiana

297. Heslop-Harrison JS. 2013. Three articles: Cyril D Darlington; Polyploidy; and (with JP Bailey) Chromosome bridge. From Brenner’s Encyclopedia of Genetics. 2nd edition. Elsevier.

Brenner’s Encyclopedia of Genetics is now edited by Kelly Hughes and Stanley Maloy With 1600 articles, it’s not too bad a price on Amazon at GBP£1,115 in hardcover (at least for a library, where several hundred students should be using it, compared to one student using a Biology textbook at 5-10% of the price) although I’m less sure about the one-user £918.76 for the Kindle edition (I’m already planning how to spend the £196.24 saving).

Abstracts below. Link to Polyploidy, Darlington, Chromosome Bridge Encyclopedia of Genetics authors preprint.

Chromosome Bridge – (single page preview shows whole article) JS Heslop-Harrison and JP Bailey

A chromosome bridge (also called chromatin bridge or ana­phase bridge) forms at anaphase of mitosis or meiosis when chromatids are not free to separate and form a bridge between two chromosomes segregating to the opposite poles (Figure 1). The chromatid forming the bridge usually breaks, leading to duplication of a segment in one daughter nucleus and deletion in the other, or it may form an acentric chromo­some fragment that is incorporated into a micronucleus or is lost. Bridges can form when a chromosome has two active centromeres (a dicentric, e.g., from a reciprocal translocation with intercalary breakpoints along chromosome arms) and
the two centromeres move to different spindle poles. Chromosome bridges may also occur when a cell divides before replication of the DNA is complete, where the unrepli­cated segment cannot separate. Ring chromosomes, formed by deletion of both terminal regions and rejoining the centric fragment ends, are frequently associated with bridges at mito­sis, arising from interlocked or dicentric rings formed following sister chromatid exchange. Repeated breakagefusion-bridge cycles may occur, leading to massive amplifica­tion of terminal DNA sequences.

Cyril D Darlington –

Cyril Dean Darlington (1903–81) was one of the influential figures in biology in the twentieth century, in particular making significant discoveries about the chromosome theory of heredity; unifying biology through the fundamental principles of evolution, cytology, genetics, and biochemistry; and making contributions to genetics and society. Building on diverse work from animals and plants, he was the first to describe clearly the nature of the partitioning and segregation of chromosomes at mitosis and the recombination events between chromatids that occur at meiosis.


Polyploid organisms are eukaryotes that have more than two complete sets of chromosomes (one from each parent or ancestor) in somatic and germline cells of animals, fungi, and plants. Polyploidy of individual cells or cell types (endopolyploidy), arising from chromosome replication without cell division, is involved in the normal (e.g., secretory cells) or abnormal (e.g., many cancers) development of organisms. Polyploidy or ‘whole-genome duplication’ is an important feature of genome evolution and speciation, and most lineages of plants and animals include rounds of such duplications in their evolutionary history. Many plant species, in particular, have both ancient whole-genome duplications and more recent polyploidy events in their ancestry. Polyploid individuals are found occasionally in all groups of eukaryotic organisms as a result of incorrect meiosis, fertilization, or cell division, although most spontaneously occurring animal polyploids are inviable. Polyploids can be generated experimentally by treatment with chemicals such as colchicine or by fusion of diploid nuclei. Many polyploids, particularly among plants, develop normally, and depending on the nature of the polyploidy may be sterile, or undergo meiosis that is indistinguishable from a normal diploid giving viable gametes.

Full Text

Link to Polyploidy, Darlington, Chromosome Bridge Encyclopedia of Genetics authors preprint.


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