page_title: Pleiotropy
section_title: Chickens
hierarchical_section_title: Pleiotropy / Examples / Chickens
caption_attribution_description: English: A chicken of the Paduan Frizzle White breed (not Polish chicken). Salon international de l'agriculture 2009, Paris, France, February 22, 2009. Français&#160;: Padoue frisée blanche - Salon international de l'agriculture 2009 - Paris - France - 22 février 2009.
context_page_description: Pleiotropy occurs when one gene influences two or more seemingly unrelated phenotypic traits. Such a gene that exhibits multiple phenotypic expression is called a pleiotropic gene. Mutation in a pleiotropic gene may have an effect on several traits simultaneously, due to the gene coding for a product used by a myriad of cells or different targets that have the same signaling function.
  Pleiotropy can arise from several distinct but potentially overlapping mechanisms, such as gene pleiotropy, developmental pleiotropy, and selectional pleiotropy. Gene pleiotropy occurs when a gene product interacts with multiple other proteins or catalyzes multiple reactions. Developmental pleiotropy occurs when mutations have multiple effects on the resulting phenotype. Selectional pleiotropy occurs when the resulting phenotype has many effects on fitness.
  An example of pleiotropy is phenylketonuria, an inherited disorder that affects the level of phenylalanine in the human body. Phenylalanine is an amino acid that can be obtained from food. Phenylketonuria causes this amino acid to increase in amount in the body, which can be very dangerous.
context_section_description: Chickens exhibit various traits affected by pleiotropic genes. Some chickens exhibit frizzle feather trait, where their feathers all curl outward and upward rather than lying flat against the body. Frizzle feather was found to stem from a deletion in the genomic region coding for α-Keratin. This gene seems to pleiotropically lead to other abnormalities like increased metabolism, higher food consumption, accelerated heart rate, and delayed sexual maturity.
  Domesticated chickens underwent a rapid selection process that led to unrelated phenotypes having high correlations, suggesting pleiotropic, or at least close linkage, effects between comb mass and physiological structures related to reproductive abilities. Both males and females with larger combs have higher bone density and strength, which allows females to deposit more calcium into eggshells. This linkage is further evidenced by the fact that two of the genes, HAO1 and BMP2, affecting medullary bone (the part of the bone that transfers calcium into developing eggshells) are located at the same locus as the gene affecting comb mass. HAO1 and BMP2 also display pleiotropic effects with commonly desired domestic chicken behavior; those chickens who express higher levels of these two genes in bone tissue produce more eggs and display less egg incubation behavior.
caption: Chicken exhibiting the frizzle feather trait
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