Abstract
There are about 10,400 living avian species belonging to the class Aves, characterized by feathers which no other animal classes possess and are warm-blooded vertebrates with four-chamber heart. They have excellent vision, and their forelimbs are modified into wings for flight or swimming, though not all can fly or swim. They lay hard-shelled eggs which are a secretory product of the reproductive system that vary greatly in colour, shape and size, and the bigger the bird, the bigger the egg. Since domestication, avian species have been basically reared for eggs, meat, pleasure and research. They reproduce sexually with the spermatozoa being homogametic and carry Z-bearing chromosomes, and the blastodisk carries either Z-bearing or W-bearing chromosomes, hence, the female is heterogametic, and thus, determines the sex of the offspring. The paired testes produce spermatozoa, sex hormones and the single ovary (with a few exceptions) produces yolk bearing the blastodisk and sex hormones. Both testis and ovary are the primary sex organs involved in sexual characteristics development in avian. In avian reproduction, there must be mating for fertile egg that must be incubated to produce the young ones. At hatch, hatchling sex is identified and reared to meet the aim of the farmer.
Reference77 articles.
1. Lederer R, Burr C. Latein für Vogelbeobachter: Über 3000 ornithologische Begriffe erklärt und erforscht, aus dem Englischen übersetzt von Susanne Kuhlmannn-Krieg. Köln: Verlag DuMont; 2014. ISBN 978-3-8321-9491-8
2. Xu X, Zhou Z, Wang X, Kuang X, Zhang F, Du X. Four-winged dinosaurs from China. Nature. 2003;421(6921):335-340. DOI: 10.1038/nature01342
3. National Geographic. Field Guide to Birds of North America. 7th ed. National Geographic; 2017. ISBN: 9781426218354.
4. Jones DN, Dekker R, Roselaar WRJ, Cees S. The Megapodes. Bird Families of the World 3. Oxford: Oxford University Press; 1995. ISBN 0-19-854651-3
5. Osinowo OA. Introduction to Animal Reproduction. Abeokuta: Sophie Academic Services Ltd.; 2006. p. 91
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