Yellow Fowls

Published 12 Oct 2017

The argument that the domestic chicken originated from a single ancestor is based on the assumption that the red jungle fowl is the sole ancestor of the domestic chicken. This argument is based on the fact that the domestic chicken resembles the red jungle fowls in a number of features such as the strong long legs and the stout bill just to mention but a few; according to Charles Darwin, whose views have been supported by molecular studies of mtDNA and retroviral insertions.

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Through the scientific arguments the paper tries to provide an explanation to the presence of yellow skin in domestic chicken. Whether a bird is yellow or white depends on the presence or absence of carotenoids.White chicken have a dominant allele while the yellow ones carry a homozygous recessive allele. This recessive gene is attributed to the regulatory mutations which inhibit expression of the beta carotenoid dehydrogenase 2 enzyme only in the skin.The mutation is regulatory because the coding sequence of the gene is intact while its regulation is modified. This enzyme is responsible for cleaving colorful carotenoids into colorless apocarotenoids thus leading to the yellow color.

Identification of the yellow skin gene involved the combination of linkage analysis and Identical -By -Decent (IBD) mapping across the various breeds with the yellow skin phenotypes. In the experiment DNA samples from various domestic breeds were used for IBD mapping where it was assumed that the yellow pigmentation was inherited from a common ancestor.Pylogenetic studies were done by sequencing 23.8kb domestic chickens homozygous for yellow skin together with a set of domestic chickens and red jungle fowls homozygous for white skin. This analysis showed great diversity between the two groups.

The study goes a head to demonstrate that though the domestic chicken inherited the mitochondrial and most of their nuclear genome from the red jungle fowls, the yellow skin allele must have originated from the grey jungle fowl. The report also includes the contribution of human beings in creating the variation. This was by introgression of the yellow skin into the red jungle fowl by hybridization after domestication of chicken.

However the experiments lacked sufficient statistics to justify why chicken with the yellow skin color are associated with high egg production. Besides the experiments have inconsistencies as regards to comparing of topologies that were derived from the control region of the mitochondrion genome and from the nuclear markers not on chromosome 24.

Otherwise the study is credible in the sense that it clearly outlines the role of regulatory mutations in evolution. It is believed that the same gene can be used to explain the pink color of flamingos and the yellow color of most prey birds.

It is also important to note that to some extend the study contradicts the assumption that the red jungle fowl is the soul wild ancestor of the domestic chicken and provides the fast conclusive evidence that other species have contributed to the genome of the chicken. This therefore necessitates changes in the taxonomy of the domestic chicken for instance from Gallus gallus domesticus to Gallus domesticus. That is to say from a monophyletic point of view to a polyphyletic perspective.

Finally the study raises a concern over the time factor. It would take a long time to break down an intrrogressive allele into a 6mb block thus its disadvantageous to domestication.

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