Genome diversity and karyotype evolution of mammals

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The 2000s witnessed an explosion of genome sequencing and mapping in evolutionarily diverse species. While full genome sequencing of mammals is rapidly progressing, the ability to assemble and align orthologous whole chromosomal regions from more than a few species is not yet possible. The intense focus on the building of comparative maps for domestic (dogs and cats), laboratory (mice and rats) and agricultural (cattle) animals has traditionally been used to understand the underlying basis of disease-related and healthy phenotypes.

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These maps also provide an unprecedented opportunity to use multispecies analysis as a tool to infer karyotype evolution. Comparative chromosome painting and related techniques are very powerful approaches in comparative genome studies. Homologies can be identified with high accuracy using molecularly defined DNA probes for fluorescence in situ hybridization (FISH) on chromosomes of different species. Chromosome painting data are now available for members of nearly all mammalian orders.

It was found that in most orders, there are species with rates of chromosome evolution that can be considered as 'default' rates. It needs to be noted that the number of rearrangements that have become fixed in evolutionary history seems relatively low, due to 180 million years of the mammalian radiation. Thus a record of the history of karyotype changes that have occurred during evolution have been attained through comparative chromosome maps.

Mammalian phylogenomics

An evolutionary tree of mammals. An evolutionary tree of mammals.svg
An evolutionary tree of mammals.

Modern mammals (class Mammalia) are divided into Monotremes, Marsupials, and Placentals. The subclass Prototheria (Monotremes) comprises the five species of egg-laying mammals: platypus and four echidna species. The infraclasses Metatheria (Marsupials) and Eutheria (Placentals) together form the subclass Theria. [4]

In the 2000s understanding of the relationships among eutherian mammals has experienced a virtual revolution. Molecular phylogenomics, new fossil finds and innovative morphological interpretations now group the more than 4600 extant species of eutherians into four major super-ordinal clades: Euarchontoglires (including Primates, Dermoptera, Scandentia, Rodentia, and Lagomorpha), Laurasiatheria (Cetartiodactyla, Perissodactyla, Carnivora, Chiroptera, Pholidota, and Eulipotyphla), Xenarthra, and Afrotheria (Proboscidea, Sirenia, Hyracoidea, Afrosoricida, Tubulidentata, and Macroscelidea). [4] This tree is very useful in unifying the parts of a puzzle in comparative mammalian cytogenetics.

Karyotypes: a global view of the genome

Each gene maps to the same chromosome in every cell. Linkage is determined by the presence of two or more loci on the same chromosome. The entire chromosomal set of a species is known as a karyotype.

A seemingly logical consequence of descent from common ancestors is that more closely related species should have more chromosomes in common. However, it is now widely thought that species may have phenetically similar karyotypes due to genomic conservation. Therefore, in comparative cytogenetics, phylogenetic relationships should be determined on the basis of the polarity of chromosomal differences (derived traits).

Historical development of comparative cytogenetics

Mammalian comparative cytogenetics, an indispensable part of phylogenomics, has evolved in a series of steps from pure description to the more heuristic science of the genomic era. Technical advances have marked the various developmental steps of cytogenetics.

Classical phase of cytogenetics

Examples of mammalian chromosomes. Examples of mammalian chromosomes.jpeg
Examples of mammalian chromosomes.

The first step of the Human Genome Project took place when Tjio and Levan, in 1956, reported the accurate diploid number of human chromosomes as 2n = 46. [6]

During this phase, data on the karyotypes of hundreds of mammalian species (including information on diploid numbers, relative length and morphology of chromosomes, presence of B chromosomes) were described. Diploid numbers (2n) were found to vary from 2n = 6–7 in the Indian muntjac [7] to over 100 in some rodents. [8]

Chromosome banding

The second step derived from the invention of C-, G-, R- and other banding techniques and was marked by the Paris Conference (1971), which led to a standard nomenclature to recognize and classify each human chromosome. [9]

G- and R- banding

The most widely used banding methods are G-banding (Giemsa-banding) and R-banding (reverse-banding). These techniques produce a characteristic pattern of contrasting dark and light transverse bands on the chromosomes. Banding makes it possible to identify homologous chromosomes and construct chromosomal nomenclatures for many species. Banding of homologous chromosomes allows chromosome segments and rearrangements to be identified. The banded karyotypes of 850 mammalian species were summarized in the Atlas of Mammalian Chromosomes. [10]

C-banding and heterochromatin

Examples of the distribution of C-heterochromatin in mammalian chromosomes. Examples of distribution of C-heterochromatin in mammalian chromosomes.jpeg
Examples of the distribution of C-heterochromatin in mammalian chromosomes.

Karyotype variability in mammals is mainly due to the varying amount of heterochromatin in each mammal. Once the amount of heterochromatin is subtracted from total genome content, all mammals have very similar genome sizes.

Mammalian species differ considerably in heterochromatin content and location. Heterochromatin is most often detected using C-banding. [12] Early studies using C-banding showed that differences in the fundamental number (i.e., the number of chromosome arms) could be entirely due to the addition of heterochromatic chromosome arms. Heterochromatin consists of different types of repetitive DNA, not all seen with C-banding that can vary greatly between karyotypes of even closely related species. The differences of the amount of heterochromatin among congeneric rodent species may reach 33% of nuclear DNA in Dipodomys species, [13] 36% in Peromyscus species, [14] 42% in Ammospermophilus [15] and 60% in Thomomys species where C-value (haploid DNA content) ranges between 2.1 and 5.6 pg. [16] [17]

The red viscacha rat (Tympanoctomys barrerae) has a record C-value among mammals—9.2 pg. [18] Although tetrapoidy was first proposed to be a reason for its high genome size and diploid chromosome number, Svartman et al. [19] showed that the high genome size was due to the enormous amplification of heterochromatin. Although one single copy gene was found to be duplicated in its genome, [20] data on absence of large genome segment duplications (single paints of most Octodon degu probes) and repetitive DNA hybridization evidence rules against tetraploidy. The study of heterochromatin composition, repeated DNA amount and its distribution on chromosomes of octodontids is absolutely necessary to define exactly what heterochromatin fraction is responsible for the large genomes of the red viscacha rat. [21]

In comparative cytogenetics, chromosome homology between species was proposed on the basis of similarities in banding patterns. Closely related species often had very similar banding pattern and after 40 years of comparing bands it seems safe to generalize that karyotype divergence in most taxonomic groups follows their phylogenetic relationship, despite notable exceptions. [10] [22]

The conservation of large chromosomal segments makes comparison between species worthwhile. Chromosome banding has been a reliable indicator of chromosome homology overall, i.e. that the chromosome identified on the basis of banding actually carries the same genes. This relationship may fail for phylogenetically distant species or species that have experienced extremely rapid chromosome evolution. Banding is still morphological and is not always a foolproof indicator of DNA content. [21]

Comparative molecular cytogenetics

A comparative chromosome map of birds' and mammals' inferred human homologies (right numbers) on chromosome idiograms Comparative chromosome map of birds and mammals inferred human homologies on chromosome idiograms.jpeg
A comparative chromosome map of birds' and mammals' inferred human homologies (right numbers) on chromosome idiograms

The third step occurred when molecular techniques were incorporated into cytogenetics. These techniques use DNA probes of diverse sizes to compare chromosomes at the DNA level. Homology can be confidently compared even between phylogenetically distant species or highly rearranged species (e.g., gibbons). Using cladistic analysis rearrangements that have diversified the mammalian karyotype are more precisely mapped and placed in a phylogenomic perspective. "Comparative chromosomics" defines the field of cytogenetics dealing with molecular approaches, [30] although "chromosomics" was originally introduced to define the research of chromatin dynamics and morphological changes in interphase chromosome structures. [31]

Chromosome painting or Zoo-FISH was the first technique to have a wide-ranging impact. [32] [33] [34] [35] [36] With this method the homology of chromosome regions between different species are identified by hybridizing DNA probes of an individual, whole chromosomes of one species to metaphase chromosomes of another species. Comparative chromosome painting allows a rapid and efficient comparison of many species and the distribution of homologous regions makes it possible to track the translocation of chromosomal evolution. When many species covering different mammalian orders are compared, this analysis can provide information on trends and rates of chromosomal evolution in different branches.

However, homology is only detected qualitatively, and resolution is limited by the size of visualized regions. Thus, the method does not detect all minuscule homologous regions from multiple rearrangements (as between mouse and human). The method also fails to report internal inversions within large segments. Another limitation is that painting across great phylogenetic distance often results in a decreased efficiency. Nevertheless, the use of painting probes derived from different species combined with comparative sequencing projects help to increase the resolution of the method. [21]

In addition to sorting, microdissection of chromosomes and chromosome regions was also used to obtain probes for chromosome painting. Best results were obtained when a series of microdissection probes covering the total human genome were localized on anthropoid primate chromosomes via multicolor banding (MCB). [37] [38] However a limitation of MCB is that it can only be used within a group of closely related species ("phylogenetic" resolution is too low). Spectral karyotyping (SKY) and MFISH—the ratio labeling and simultaneous hybridization of a complete chromosomal set have similar drawbacks and little application outside of clinical studies. [21]

Comparative genomics data including chromosome painting confirmed the substantial conservation of mammalian chromosomes. [36] Total human chromosomes or their arms can efficiently paint extended chromosome regions in many placentals down to Afrotheria and Xenarthra. Gene localization data on human chromosomes can be extrapolated to the homologous chromosome regions of other species with high reliability. Usefully, humans express conserved syntenic chromosome organization similar to the ancestral condition of all placental mammals.

Post-genomic time and comparative chromosomics

After the Human Genome Project researchers focused on evolutionary comparisons of the genome structures of different species. The whole genome of any species can be sequenced completely and repeatedly to obtain a comprehensive single-nucleotide map. This method makes it possible to compare genomes for any two species regardless of their taxonomic distance.

Sequencing efforts provided a variety of products useful in molecular cytogenetics. Fluorescence in situ hybridization (FISH) with DNA clones (BAC and YAC clones, cosmids) allowed the construction of chromosome maps at a resolution of several megabases that could detect relatively small chromosome rearrangements. A resolution of several kilobases can be achieved on interphase chromatin. A limitation is that hybridization efficiencies decrease with increasing phylogenetic distance.

Radiation hybrid (RH) genome mapping is another efficient approach. This method includes the irradiation of cells to disrupt the genome into the desired number of fragments that are subsequently fused with Chinese hamster cells. The resulting somatic cell hybrids contain individual fragments of the relevant genome. Then, 90–100 (sometimes, more) clones covering the total genome are selected, and the sequences of interest are localized on the cloned fragments via the polymerase chain reaction (PCR) or direct DNA–DNA hybridization. To compare the genomes and chromosomes of two species, RHs should be obtained for both species. [21]

Sex chromosome evolution

In contrast to many other taxa, therian mammals and birds are characterized by highly conserved systems of genetic sex determination that lead to special chromosomes, i.e. the sex chromosomes. Although the XX/XY sex chromosome system is the most common among eutherian species, it is not universal. In some species X-autosomal translocations result in the appearance of "additional Y" chromosomes (for example, XX/XY1Y2Y3 systems in black muntjac). [39] [40]

In other species Y-autosomal translocations lead to appearance of additional X chromosomes (for example, in some New World primates such as howler monkeys). Regarding this aspect, rodents again represent a peculiar derived group, comprising the record number of species with non-classical sex chromosomes such as the wood lemming, the collared lemming, the creep vole, the spinous country rat, the Akodon and the bandicoot rat. [41]

Related Research Articles

<span class="mw-page-title-main">Chromosome</span> DNA molecule containing genetic material of a cell

A chromosome is a package of DNA with part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells the most important of these proteins are the histones. These proteins, aided by chaperone proteins, bind to and condense the DNA molecule to maintain its integrity. These chromosomes display a complex three-dimensional structure, which plays a significant role in transcriptional regulation.

<span class="mw-page-title-main">Euchromatin</span> Lightly packed form of chromatin that is enriched in genes

Euchromatin is a lightly packed form of chromatin that is enriched in genes, and is often under active transcription. Euchromatin stands in contrast to heterochromatin, which is tightly packed and less accessible for transcription. 92% of the human genome is euchromatic.

<span class="mw-page-title-main">Karyotype</span> Photographic display of total chromosome complement in a cell

A karyotype is the general appearance of the complete set of chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is discerned by determining the chromosome complement of an individual, including the number of chromosomes and any abnormalities.

<span class="mw-page-title-main">Y chromosome</span> Sex chromosome in the XY sex-determination system

The Y chromosome is one of two sex chromosomes in therian mammals and other organisms. Along with the X chromosome, it is part of the XY sex-determination system, in which the Y is the sex-determining because it is the presence or absence of Y chromosome that determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the SRY gene, which triggers development of male gonads. The Y chromosome is passed only from male parents to male offspring.

<span class="mw-page-title-main">Afrotheria</span> Clade of mammals containing elephants and elephant shrews

Afrotheria is a superorder of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews, otter shrews, tenrecs, aardvarks, hyraxes, elephants, sea cows, and several extinct clades. Most groups of afrotheres share little or no superficial resemblance, and their similarities have only become known in recent times because of genetics and molecular studies. Many afrothere groups are found mostly or exclusively in Africa, reflecting the fact that Africa was an island continent from the Cretaceous until the early Miocene around 20 million years ago, when Afro-Arabia collided with Eurasia.

<span class="mw-page-title-main">Cytogenetics</span> Branch of genetics

Cytogenetics is essentially a branch of genetics, but is also a part of cell biology/cytology, that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis and meiosis. Techniques used include karyotyping, analysis of G-banded chromosomes, other cytogenetic banding techniques, as well as molecular cytogenetics such as fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH).

<span class="mw-page-title-main">Comparative genomics</span> Field of biological research

Comparative genomics is a branch of biological research that examines genome sequences across a spectrum of species, spanning from humans and mice to a diverse array of organisms from bacteria to chimpanzees. This large-scale holistic approach compares two or more genomes to discover the similarities and differences between the genomes and to study the biology of the individual genomes. Comparison of whole genome sequences provides a highly detailed view of how organisms are related to each other at the gene level. By comparing whole genome sequences, researchers gain insights into genetic relationships between organisms and study evolutionary changes. The major principle of comparative genomics is that common features of two organisms will often be encoded within the DNA that is evolutionarily conserved between them. Therefore, Comparative genomics provides a powerful tool for studying evolutionary changes among organisms, helping to identify genes that are conserved or common among species, as well as genes that give unique characteristics of each organism. Moreover, these studies can be performed at different levels of the genomes to obtain multiple perspectives about the organisms.

Comparative genomic hybridization (CGH) is a molecular cytogenetic method for analysing copy number variations (CNVs) relative to ploidy level in the DNA of a test sample compared to a reference sample, without the need for culturing cells. The aim of this technique is to quickly and efficiently compare two genomic DNA samples arising from two sources, which are most often closely related, because it is suspected that they contain differences in terms of either gains or losses of either whole chromosomes or subchromosomal regions. This technique was originally developed for the evaluation of the differences between the chromosomal complements of solid tumor and normal tissue, and has an improved resolution of 5–10 megabases compared to the more traditional cytogenetic analysis techniques of giemsa banding and fluorescence in situ hybridization (FISH) which are limited by the resolution of the microscope utilized.

<span class="mw-page-title-main">Constitutive heterochromatin</span>

Constitutive heterochromatin domains are regions of DNA found throughout the chromosomes of eukaryotes. The majority of constitutive heterochromatin is found at the pericentromeric regions of chromosomes, but is also found at the telomeres and throughout the chromosomes. In humans there is significantly more constitutive heterochromatin found on chromosomes 1, 9, 16, 19 and Y. Constitutive heterochromatin is composed mainly of high copy number tandem repeats known as satellite repeats, minisatellite and microsatellite repeats, and transposon repeats. In humans these regions account for about 200Mb or 6.5% of the total human genome, but their repeat composition makes them difficult to sequence, so only small regions have been sequenced.

<span class="mw-page-title-main">Polysomy</span> Abnormal multiples of one or more chromosomes

Polysomy is a condition found in many species, including fungi, plants, insects, and mammals, in which an organism has at least one more chromosome than normal, i.e., there may be three or more copies of the chromosome rather than the expected two copies. Most eukaryotic species are diploid, meaning they have two sets of chromosomes, whereas prokaryotes are haploid, containing a single chromosome in each cell. Aneuploids possess chromosome numbers that are not exact multiples of the haploid number and polysomy is a type of aneuploidy. A karyotype is the set of chromosomes in an organism and the suffix -somy is used to name aneuploid karyotypes. This is not to be confused with the suffix -ploidy, referring to the number of complete sets of chromosomes.

<span class="mw-page-title-main">Boreoeutheria</span> Magnorder of mammals containing Laurasiatheria and Euarchontoglires

Boreoeutheria is a magnorder of placental mammals that groups together superorders Euarchontoglires and Laurasiatheria. With a few exceptions, male boreoeutherians have a scrotum, an ancestral feature of the clade. The sub-clade Scrotifera was named after this feature.

<span class="mw-page-title-main">Molecular cytogenetics</span>

Molecular cytogenetics combines two disciplines, molecular biology and cytogenetics, and involves the analysis of chromosome structure to help distinguish normal and cancer-causing cells. Human cytogenetics began in 1956 when it was discovered that normal human cells contain 46 chromosomes. However, the first microscopic observations of chromosomes were reported by Arnold, Flemming, and Hansemann in the late 1800s. Their work was ignored for decades until the actual chromosome number in humans was discovered as 46. In 1879, Arnold examined sarcoma and carcinoma cells having very large nuclei. Today, the study of molecular cytogenetics can be useful in diagnosing and treating various malignancies such as hematological malignancies, brain tumors, and other precursors of cancer. The field is overall focused on studying the evolution of chromosomes, more specifically the number, structure, function, and origin of chromosome abnormalities. It includes a series of techniques referred to as fluorescence in situ hybridization, or FISH, in which DNA probes are labeled with different colored fluorescent tags to visualize one or more specific regions of the genome. Introduced in the 1980s, FISH uses probes with complementary base sequences to locate the presence or absence of the specific DNA regions. FISH can either be performed as a direct approach to metaphase chromosomes or interphase nuclei. Alternatively, an indirect approach can be taken in which the entire genome can be assessed for copy number changes using virtual karyotyping. Virtual karyotypes are generated from arrays made of thousands to millions of probes, and computational tools are used to recreate the genome in silico.

<span class="mw-page-title-main">Plains viscacha rat</span> Species of rodent

The plains viscacha rat, plains vizcacha rat, red viscacha rat, or red vizcacha rat is a species of rodent in the family Octodontidae native to Argentina. It is one of three species in the genus Tympanoctomys.

<span class="mw-page-title-main">Bovini</span> Tribe of cattle

The tribe Bovini or wild cattle are medium to massive bovines that are native to Eurasia, North America, and Africa. These include the enigmatic, antelope-like saola, the African and Asiatic buffalos, and a clade that consists of bison and the wild cattle of the genus Bos. Not only are they the largest members of the subfamily Bovinae, they are the largest species of their family Bovidae. The largest species is the gaur, weighing up to 1,500 kg (3,300 lb).

<span class="mw-page-title-main">Octodontidae</span> Family of rodents

Octodontidae is a family of rodents, restricted to southwestern South America. Fourteen species of octodontid are recognised, arranged in seven genera. The best known species is the common degu, Octodon degus.

Virtual karyotype is the digital information reflecting a karyotype, resulting from the analysis of short sequences of DNA from specific loci all over the genome, which are isolated and enumerated. It detects genomic copy number variations at a higher resolution for level than conventional karyotyping or chromosome-based comparative genomic hybridization (CGH). The main methods used for creating virtual karyotypes are array-comparative genomic hybridization and SNP arrays.

<span class="mw-page-title-main">Microchromosome</span> Type of chromosome

A microchromosome is a chromosome defined for its relatively small size. They are typical components of the karyotype of birds, some reptiles, fish, amphibians, and monotremes. As many bird genomes have chromosomes of widely different lengths, the name was meant to distinguish them from the comparatively large macrochromosomes. The distinction referred to the measured size of the chromosome while staining for karyotype, and while there is not a strict definition, chromosomes resembling the large chromosomes of mammals were called macrochromosomes, while the much smaller ones of less than around 0.5 μm were called microchromosomes. In terms of base pairs, by convention, those of less than 20Mb were called microchromosomes, those between 20 and 40 Mb are classified as intermediate chromosomes, and those larger than 40Mb are macrochromosomes. By this definition, all normal chromosomes in organisms with relatively small genomes would be considered microchromosomes.

<span class="mw-page-title-main">Cytotaxonomy</span>

Cytotaxonomy is the classification of organisms using comparative studies of chromosomes during mitosis.

Henry HQ Heng is a professor of molecular medicine and genetics and of pathology at the Wayne State University School of Medicine. Heng first received his PhD from the University of Toronto Hospital for Sick Children in 1994, mentored by Lap-Chee Tsui. He then completed his post-doc under Peter Moens at York University, before joining the Wayne State University School of Medicine faculty.

References

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  27. ↑ Yang, F.; O'Brien, P. C.; Milne, B. S.; Graphodatsky, A. S.; Solanky, N.; Trifonov, V.; Rens, W.; Sargan, D.; Ferguson-Smith, M. A. (1999). "A complete comparative chromosome map for the dog, red fox, and human and its integration with canine genetic maps". Genomics. 62 (2): 189–202. doi:10.1006/geno.1999.5989. PMID   10610712.
  28. ↑ Graphodatsky, A. S.; Kukekova, A. V.; Yudkin, D. V.; Trifonov, V. A.; Vorobieva, N. V.; Beklemisheva, V. R.; Perelman, P. L.; Graphodatskaya, D. A.; Trut, L. N.; Yang, F. T. (2005). "The proto-oncogene C-KIT maps to canid B-chromosomes". Chromosome Research. 13 (2): 113–122. CiteSeerX   10.1.1.535.2213 . doi:10.1007/s10577-005-7474-9. PMID   15861301. S2CID   22541652.
  29. ↑ a. Reconstructed karyotype of the ancestral Eutherian genome. [23] Each chromosome is assigned a specific color. These colors are used for mark homologies in idiograms of chromosomes of other species (5b–5i) b. Idiogram of chicken (Gallus gallus domesticus, 2n = 78) chromosomes. The reconstruction is based on alignments of chicken and human genome sequences. [24] c. Idiogram of short-tailed opossum (Monodelphis domestica, 2n = 18) chromosomes. The reconstruction is based on alignments of opossum and human genome sequences. [24] d. Idiogram of aardvark (Orycteropus afer, 2n = 20) chromosomes. The reconstruction is based on painting data. [23] e. Idiogram of mink (Mustela vison, 2n = 30) chromosomes. The reconstruction is based on painting data. [25] [26] f. Idiogram of the Red fox (Vulpes vulpes, 2n = 34 + 0-8 B's) chromosomes. The reconstruction is based on painting and mapping data. [27] [28] g. Reconstructed karyotype of the ancestral Sciuridae (Rodentia) genome, based on painting data (Li et al., 2004). h. Idiogram of the House mouse (Mus musculus, 2n = 40) chromosomes. The reconstruction is based on alignments of Mus and human genome sequences. [24] i. Idiogram of human (Homo sapiens, 2n = 46) chromosomes.
  30. ↑ Grafodatskii, A. S. (2007). "[Comparative chromosomics]". Mol Biol (Mosk). 41 (3): 408–422. PMID   17685220.
  31. ↑ Claussen, U. (2005). "Chromosomics". Cytogenet Genome Res. 111 (2): 101–106. doi:10.1159/000086377. PMID   16103649. S2CID   232274929.
  32. ↑ Wienberg, J.; Jauch, A.; Stanyon, R.; Cremer, T. (1990). "Molecular cytotaxonomy of primates by chromosomal in situ suppression hybridization". Genomics. 8 (2): 347–350. doi:10.1016/0888-7543(90)90292-3. PMID   2249853.
  33. ↑ Telenius, H.; Pelmear, A. H.; Tunnacliffe, A.; Carter, N. P.; Behmel, A.; Fergusonsmith, M. A.; Nordenskjold, M.; Pfragner, R.; Ponder, B. A. J. (1992). "Cytogenetic Analysis by Chromosome Painting Using Dop-Pcr Amplified Flow-Sorted Chromosomes". Gene Chromosome Canc. 4 (3): 257–263. doi:10.1002/gcc.2870040311. PMID   1382568. S2CID   40658335.
  34. ↑ Scherthan, H.; Cremer, T.; Arnason, U.; Weier, H. U.; Limadefaria, A.; Fronicke, L. (1994). "Comparative Chromosome Painting Discloses Homologous Segments in Distantly Related Mammals". Nature Genetics. 6 (4): 342–347. doi:10.1038/ng0494-342. PMID   8054973. S2CID   30936697.
  35. ↑ Ferguson-Smith, M. A. (1997). "Genetic analysis by chromosome sorting and painting: phylogenetic and diagnostic applications". Eur J Hum Genet. 5 (5): 253–265. doi:10.1159/000484775. PMID   9412781.
  36. 1 2 Ferguson-Smith, M. A.; V. Trifonov (2007). "Mammalian karyotype evolution". Nat Rev Genet. 8 (12): 950–962. doi:10.1038/nrg2199. PMID   18007651. S2CID   7814586.
  37. ↑ Mrasek, K.; Heller, A.; Rubtsov, N.; Trifonov, V.; Starke, H.; Rocchi, M.; Claussen, U.; Liehr, T. (2001). "Reconstruction of the female Gorilla gorilla karyotype using 25-color FISH and multicolor banding (MCB)". Cytogenetics and Cell Genetics. 93 (3–4): 242–248. doi:10.1159/000056991 (inactive 2024-06-22). PMID   11528119. S2CID   38770817.{{cite journal}}: CS1 maint: DOI inactive as of June 2024 (link)
  38. ↑ Mrasek, K.; Heller, A.; Rubtsov, N.; Trifonov, V.; Starke, H.; Claussen, U.; Liehr, T. (2003). "Detailed Hylobates lar karyotype defined by 25-color FISH and multicolor banding". International Journal of Molecular Medicine. 12 (2): 139–146. doi:10.3892/ijmm.12.2.139. PMID   12851708.
  39. ↑ Yang, F.; Carter, N. P.; Shi, L.; Ferguson-Smith, M. A. (1995). "A comparative study of karyotypes of muntjacs by chromosome painting". Chromosoma. 103 (9): 642–652. doi:10.1007/BF00357691. PMID   7587587. S2CID   681115.
  40. ↑ Huang, L.; Chi, J.; Wang, J.; Nie, W.; Su, W.; Yang, F. (2006). "High-density comparative BAC mapping in the black muntjac (Muntiacus crinifrons): molecular cytogenetic dissection of the origin of MCR 1p+4 in the X1X2Y1Y2Y3 sex chromosome system". Genomics. 87 (5): 608–615. doi: 10.1016/j.ygeno.2005.12.008 . PMID   16443346.
  41. ↑ Fredga, K. (1983). "Aberrant Sex Chromosome Mechanisms in Mammals Evolutionary Aspects: Evolutionary Aspects". Mechanisms of Gonadal Differentiation in Vertebrates. Vol. 23 Suppl. pp. S23–30. doi:10.1007/978-3-642-69150-8_4. ISBN   978-3-540-12480-1. PMID   6444170.{{cite book}}: |journal= ignored (help)
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