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Y linkage, also known as holandric inheritance (from Ancient Greek ὅλος hólos, "whole" + ἀνδρός andrós, "male"),[1] describes traits that are produced by genes located on the Y chromosome. It is a form of sex linkage.
Y linkage can be difficult to detect. This is partly because the Y chromosome is small and contains fewer genes than the autosomal chromosomes or the X chromosome. It is estimated to contain about 200 genes. Earlier, the human Y chromosome was thought to have little importance;.[2] Although the Y-chromosome is sex-determining in humans and some other species, not all genes that play a role in sex determination are Y-linked. The Y-chromosome, generally does not undergo genetic recombination and only small regions called pseudoautosomal regions exhibit recombination. The majority of the Y-chromosome genes that do not recombine are located in the "non-recombining region".[3]
For a trait to be considered Y linkage, it must exhibit these characteristics:
- occurs only in males
- appears in all sons of males who exhibit that trait
- is absent from daughters of trait carriers; instead the daughters that are phenotypically normal and do not have affected offspring.[4]
These requirements were established by the pioneer of Y linkage, Curt Stern. Stern detailed in his paper genes he suspected to be Y-linked.[4] His requirements at first made Y linkage hard to prove. In the 1950s using human pedigrees, many genes were incorrectly determined to be Y-linked.[5] Later research adopted more advanced techniques and more sophisticated statistical analysis.[6] Hairy ears are an example of a gene once thought to be Y-linked in humans; however, that hypothesis was discredited.[5] Due to advancements in DNA sequencing, Y linkage is getting easier to determine and prove. The Y-chromosome has been entirely mapped,[7] revealing many Y-linked traits.[8]
Y linkage is similar to, but different from X linkage; although, both are forms of sex linkage. X linkage can be genetically linked and sex-linked, while Y linkage can only be genetically linked. This is because males' cells have only one copy of the Y-chromosome. X-chromosomes have two copies, one from each parent permitting recombination. The X chromosome contains more genes and is substantially larger.
Some ostensibly Y-linked traits have not been confirmed. One example is hearing impairment. Hearing impairment was tracked in one specific family and through seven generations all males were affected by this trait. However, this trait occurs rarely and has not been entirely resolved.[9]
Y-chromosome deletions are a frequent genetic cause of male infertility.
- ^ "Definition of holandric | Dictionary.com". www.dictionary.com. Retrieved 2020-01-21.
- ^ Sayres, Wilson (2012). "Gene survival and death on the human Y chromosome". Mol Biol Evol. 30 (4): 781–87. doi:10.1093/molbev/mss267. PMC 3603307. PMID 23223713.
- ^ Skaletsky, Helen (2003). "The male-specific region of the human Y chromosome is a mosaic of discrete sequence classes". Nature. 423 (6942): 825–837. Bibcode:2003Natur.423..825S. doi:10.1038/nature01722. PMID 12815422.
- ^ a b Curt, Stern (1957). "The Problem of Complete Y-Linkage in Man". American Journal of Human Genetics. 9 (3): 147–166. PMC 1931892. PMID 13469791.
- ^ a b Lee, Andrew (2004). "Molecular evidence for absence of Y-linkage of the Hairy Ears trait". European Journal of Human Genetics. 112 (12): 1077–1079. doi:10.1038/sj.ejhg.5201271. PMID 15367914.
- ^ Ott, J (1986). "Y-linkage and pseudoautosomal linkage". Am J Hum Genet. 38 (6): 891–7. PMC 1684847. PMID 3728465.
- ^ Rhie, A.; et al. (2023). "The complete sequence of a human y chromosome". Nature. 621 (7978): 344–354. Bibcode:2023Natur.621..344R. doi:10.1038/s41586-023-06457-y. PMC 10752217. PMID 37612512.
- ^ Cerf, Emily. "Scientists release the first complete sequence of a human Y chromosome". UC Santa Cruz News. Retrieved 2024-04-25.
- ^ Wang, Qiuju (2013). "Genetic Basis of Y-Linked Hearing Impairment". Am J Hum Genet. 92 (2): 301–6. doi:10.1016/j.ajhg.2012.12.015. PMC 3567277. PMID 23352258.