Principles of Genetics and Breeding

4.2.2 Y–Linked Genes

Only one copy of a Y- linked gene exists on the single Y chromosome of a normal male. Y- linked phenotypes cannot be fixed in normal females, which do not possess Y chromosome. Because males have only one Y chromosome, a Y- linked allele’s phenotype is always expressed.

• The Y–linked inheritance of colour patterns in male P. reticulata was reported by O. Winge (1992).
• Genes located on the Y–chromosomes are transmitted from father to son, and unless they cross over to the X chromosome, they will never exist in normal females (XX).
• Thus Y-linked phenotypes are seen in only one sex, males.
• Phenotypes that are Y – linked in the guppy are :

Yma – maculatus pigmentation,

Yds–double sword tail and

Yar –armatus pigmentation.

• The maculatus gene in the guppy, which controls the maculatus pigment pattern (black spot on the dorsal fin and a red spot on the body) will be used to illustrate the inheritance of a Y-linked phenotype. The symbol for the maculatus gene is Yma.
• The symbol for the allele which produces the wild type or unspotted phenotype is Y. The alleles having strong effects on male size are Y-linked in Xiphophorus variatus.

Genotype	Phenotype
XX	grey O+
XYma	maculatus♂
XY	grey ♂