[ **up [[Animals]] | [[Chordates]]** ] --- # Mammals [[2025-0320. 'Mammals are distinguished by the ability to nurse their young. Lactation has been a crucial factor in the evolution of mammalian parental investment and reproductive strategies ...'|'Mammals are distinguished by the ability to nurse their young. Lactation has been a crucial factor in the evolution of mammalian parental investment and reproductive strategies ...']][^1] --- ## Taxonomy - **[[Life (Biology)]]** - **[[Eukaryotes|Eukaryota (Domain)]]** - **[[Animals|Animalia (Kingdom)]]** - [[Chordates|Chordata (Phylum)]] - [[Mammals|Mammalia (Class)]] <small>MAMMALS</small> ---- ## Description ### Lactation [[2025-0320. 'Mammals are distinguished by the ability to nurse their young. Lactation has been a crucial factor in the evolution of mammalian parental investment and reproductive strategies ...'|'Mammals are distinguished by the ability to nurse their young. Lactation has been a crucial factor in the evolution of mammalian parental investment and reproductive strategies ...']][^1] (*See also:* [[Lactation]]) ### Sex determination #### XX/XY sex determination system - *See:* [[Therians#Sex determination|Therian XX/XY sex determination system]] ##### SRY gene [[2025-0323. 'Mammalian sex is in fact regulated by a single gene on the Y chromosome - SRY. ... In the absence of this gene, gonads develop into ovaries.'|'Mammalian sex is in fact regulated by a single gene on the Y chromosome: SRY (Sex-determining Region of the Y chromosome). The SRY gene is at the top of the gene activity cascade which triggers testis formation and thus male development (Sinclair et al. 1990). In the absence of this gene, gonads develop into ovaries.']][^2] [[2025-0323. 'It has generally been assumed that heteromorphic sex chromosomes with a highly degraded and specialized Y chromosome, such as that found in mammals, are a strong barrier to transitions between sex-determining systems.'|'It has generally been assumed that heteromorphic sex chromosomes with a highly degraded and specialized Y chromosome, such as that found in mammals, are a strong barrier to transitions between sex-determining systems. This is owing to formation of lethal genotypes (such as YY) and the potential adverse effects of Y-chromosome genes on the feminization process of neo-XY females or, conversely, the lack of necessary Y-chromosome genes in neo-XX males (Bull 1983; Marin & Baker 1998).']][^3] ###### Exceptions to the rule [[2025-0313. 'In mammals, there are indeed a few natural exceptions to the standard XX-XY sex determination system.'|’In mammals, there are indeed a few natural exceptions to the standard XX/XY sex determination system.’]][^4] Or, to put it another way, “[[2025-0313. '... mammalian lineages present atypical sex chromosomes that have evolved through millions of years of natural selection.'|'mammalian lineages present atypical sex chromosomes that have evolved through millions of years of natural selection.']][^5] [[2025-0323. 'A limited number of mammal species do, however, escape this constraint and present atypical sex chromosome systems.'|'A limited number of mammal species do, however, escape this constraint and present atypical sex chromosome systems.']][^6] All [[Rodents|rodents]], they can be grouped into four categories: - [[2025-0323. 'So far, these unusual sex-determining systems have been unambiguously identified by molecular or cytogenomic methods in seven genera, all rodents, which group in four categories.'|(i) XX or XY females and XY males]].[^7] - present in the [[Lemmings|lemmings]] *[[Wood lemming|Myopus schisticolor]]* and *[[Arctic lemming|Dicrostonyx torquatus]]*.[^8] - as well as several species of the South American field mouse *[[Akodon (Genus)]]*.[^9] + [[2025-0323. 'So far, these unusual sex-determining systems have been unambiguously identified by molecular or cytogenomic methods in seven genera, all rodents, which group in four categories.'|(ii) XO females (only one) and XY males]].[^10] + present in the vole *[[Creeping vole|Microtus oregoni]]*.[^11] - [[2025-0323. 'So far, these unusual sex-determining systems have been unambiguously identified by molecular or cytogenomic methods in seven genera, all rodents, which group in four categories.'| (iii) females and males with an identical XO karyotype (loss of the second X chromosome in females and of the Y in males)]][^12] - present in the Japanese spiny rats *[[Ryuku spiny rat|Tokudaia osimensis]]* and *[[Tokunoshima spiny rat|Tokudaia tokunoshimensis]]*.[^13] - present in the mole vole *[[Transcaucasian mole vole|Bramus lutescens]]*.[^14] + [[2025-0323. 'So far, these unusual sex-determining systems have been unambiguously identified by molecular or cytogenomic methods in seven genera, all rodents, which group in four categories.'|(iv) XX males and females]].[^15] + present in *[[Zaisan mole vole|Ellobius tancrei]]* and *[[Northern mole vole|Ellobius talpinus]]*.[^16] [[2025-0323. 'So far, these unusual sex-determining systems have been unambiguously identified by molecular or cytogenomic methods in seven genera, all rodents, which group in four categories.'|’Categories (iii) and (iv) are remarkable since sex determination occurs in the absence of a Y chromosome, and even without the Sry gene.’]][^17] ##### Fertile XX, XX* & X\*Y females, XY males - [[African pygmy mouse#Four Sexes Male (XY) + Female (XX, XX* & X *Y)|African pygmy mouse: Male (XY) + Female (XX, XX* & X*Y)]] ----- ## Habits ### Pheromones Some mammals have calming (appeasement) pheromones.[^18] [^1]: Avery Nelson Gilbert, ‘[[Gilbert. ‘Mammary number and litter size in Rodentia_ The “one-half rule”’, 1986.|Mammary number and litter size in Rodentia: The "one-half rule"]]’, *Proceedings of the National Academy of Sciences of the United States of America*, vol. 83, no. 13 (1 July 1986), p. 4828. [^2]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1049. [^3]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1049. [^4]: P. A. Saunders, et al., ‘[[Saunders, et al. ‘Masculinised behaviour of XY females in mammal with naturally occurring sex reversal’, 2016.|Masculinised behaviour of XY females in a mammal with naturally occurring sex reversal]]’, *Scientific Reports*, vol. 6 (11 March 2016), p. 1. [^5]: Frédéric Baudat, Bernard de Mass & Frederic Veyrunes, ‘[[Baudat, de Mass & Veyrunes. ‘Sex chromosome quadrivalents in oocytes of the African pygmy mouse Mus minutoides that harbors non-conventional sex chromosomes’, 2019.|Sex chromosome quadrivalents in oocytes of the African pygmy mouse Mus minutoides that harbors non-conventional sex chromosomes]]’, *Chromosoma*, vol. 128, issue 3 (2019), p. 398. [^6]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1049. [^7]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1049. [^8]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1049. [^9]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1050. [^10]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1050. [^11]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1050. [^12]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1050. [^13]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1050. [^14]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1050. [^15]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1050. [^16]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1050. [^17]: Frederic Veyrunes, et al., ‘[[Veyrunes, et al. 'A novel sex determination system in a close relative of the house mouse', 2010.|A novel sex determination system in a close relative of the house mouse]]’, *Proceedings of the Royal Society B: Biological Sciences*, vol. 277, issue 1684 (7 April 2010), p. 1050. [^18]: ‘Pheromone’, *Wikipedia*, updated 4 January 2025, https://en.wikipedia.org/wiki/Pheromone.