In birds the sex chromosomes are controlled genetically and the structure of determining an offspring is contradictory to that in mammals: the male is the one with homogametic sex (ZZ) where the female is heterogametic (ZW). THESE sex chromosomes are designated as Z and W. The males are ZZ on the other hand the females are ZW.
Genes on Z chromosomes act just like X-linked genes in mammals, except that hemizygosity is found in females.In comparison to the XY sex-determination system and the X0 sex-determination system, where the sperm determines the sex, in the ZW system, the ovum determines the sex of the coming offspring. .also The Z chromosome is larger and has more genes, same as X chromosome in the XY system.
While, there has not been much substantialexploration on the other organisms with ZW sex-determination system, researchers declared that chickens’ sex chromosomes do not reveal any sort of chromosome-wide measured compensation, and instead they seem to dosage compensate on a gene-by-gene basis. Further research expanded the list of various birds that do not show any sort of chromosome-wide dosage compensation like crows and ratites, hence, implying that every avian chromosomes is deficient in chromosome-wide dosage compensation.Additionally, the involvement of sex-biased miRNAs was put forth to compensate for the existence of 2 Z-chromosomes in all the male birds.
It is still unknown whether it might be the existence of the W chromosome what induces the female features, or rather it is the replicationof the Z chromosome that prompts the male ones; in contrary to mammals, never a bird with a double W chromosome (ZWW) or a single Z (Z0) have been found.
However, it is known that the removal or damage to the ovaries of female birds can steer towards the development of male plumage, considering that female hormones subdue the embodiment of male characteristics in birds. It seems feasible that either condition could result in embryonic death, or that both chromosomes could be accountable for sex selection and choosing.There isone attainable gene that could determine that sex in birds is the DMRT1 inbred. Studies have shown that two copies of the gene are important for male sex verification.
The ZW sex-determination system empower us to create sex link in chickens where color of them at hatching is recognized by sex. A number of different practical methods have been developed to determine the sex of birds, based on sex-linked inbred, the number of DNA per cell and using DNA scrutiny for sex-linked sequences.