Ep 14

As for plants and animals, fungal hybrids and polyploids display structural and functional modifications compared to their progenitors and diploid counterparts. In particular, the structural and functional outcomes of polyploid Saccharomyces genomes strikingly reflect the evolutionary fate of plant polyploid ones. Large chromosomal rearrangements[83] leading to chimeric chromosomes[84] have been described, as well as more punctual genetic modifications such as gene loss.[85] The homoealleles of the allotetraploid yeast S. pastorianus show unequal contribution to the transcriptome.[86] Phenotypic diversification is also observed following polyploidization and/or hybridization in fungi,[87] producing the fuel for natural selection and subsequent adaptation and speciation.

Each Deinococcus radiodurans bacterium contains 4-8 copies of its chromosome.[92] Exposure of D. radiodurans to X-ray irradiation or desiccation can shatter its genomes into hundred of short random fragments. Nevertheless, D. radiodurans is highly resistant to such exposures. The mechanism by which the genome is accurately restored involves RecA-mediated homologous recombination and a process referred to as extended synthesis-dependent strand annealing (SDSA).[93]

Azotobacter vinelandii can contain up to 80 chromosome copies per cell.[94] However this is only observed in fast growing cultures, whereas cultures grown in synthetic minimal media are not polyploid.[95]

Archaea

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The archaeon Halobacterium salinarium is polyploid[96] and, like Deinococcus radiodurans, is highly resistant to X-ray irradiation and desiccation, conditions that induce DNA double-strand breaks.[97] Although chromosomes are shattered into many fragments, complete chromosomes can be regenerated by making use of overlapping fragments. The mechanism employs single-stranded DNA binding protein and is likely homologous recombinational

Polyploidy is a condition in which the cells of an organism have more than one pair of (homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains one or more chromosomes and comes from each of two parents, resulting in pairs of homologous chromosomes between sets. However, some organisms are polyploid. Polyploidy is especially common in plants. Most eukaryotes have diploid somatic cells, but produce haploid gametes (eggs and sperm) by meiosis. A monoploid has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Males of bees and other Hymenoptera, for example, are monoploid. Unlike animals, plants and multicellular algae have life cycles with two alternating multicellular generations. The gametophyte generation is haploid, and produces gametes by mitosis, the sporophyte generation is diploid and produces

Polyploidy may occur due to abnormal cell division, either during mitosis, or more commonly from the failure of chromosomes to separate during meiosis or from the fertilization of an egg by more than one sperm.[1] In addition, it can be induced in plants and cell cultures by some chemicals: the best known is colchicine, which can result in chromosome doubling, though its use may have other less obvious consequences as well. Oryzalin will also double the existing chromosome content.

Polyploidy occurs in highly differentiated human tissues in the liver, heart muscle, bone marrow and the placenta.[2][failed verification] It occurs in the somatic cells of some animals, such as goldfish,[3] salmon, and salamanders, but is especially common among ferns and flowering plants (see Hibiscus rosa-sinensis), including both wild and cultivated species. Wheat, for example, after millennia of hybridization and modification by humans, has strains that are diploid (two sets of chromosomes), tetraploid (four sets of chromosomes) with the common name of durum or macaroni wheat, and hexaploid (six sets of chromosomes) with the common name of bread wheat. Many agriculturally important plants of the genus Brassica are also tetraploids. Sugarcane can have

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