Working in the early 20th century T.H. Morgan, was the first to use Drosophila to explore heredity. Primarily on the basis of work with D. melanogaster, Morgan and his colleagues C.B. Bridges, A.H. Sturtevant, and H.J. Mueller developed a chromosome theory of heredity, for which Morgan was awarded a Nobel Prize in 1933. Their experiments consisted of cross-breeding Drosophila mutants and documenting offspring. Another highly regarded figure in Drosophila research was Theodosius Dobzhansky, who invented the use of genetic markers and used them to study hybrid sterility between Drosophila pseudoobscura and Drosophila persimilis ( Futuyma 1997 ). This experimental method has been used for many years. Experiments involving crosses between D. pseudoananassae and D. bipectinata, D. pseudoananassae and D. parabipectinata, and D. pseudoananassae and D. malerkotliana have further shown that the Y chromosome has a role in hybrid male sterility. The possible interactions of Y chromosome are X-Y, Y-autosome and Y-cytoplasm ( Paras 2006 ). The sterile males carry a set of conspecific autosomes to the Y chromosome, which results in fertility because of the Y-dominant autosome interactions. Therefore, Y-autosome interactions are ruled out in this type of hybrid sterility. Since cytoplasmic factors can be compatible between these species (Reference needed) , such factors are also dismissed as the cause of sterility. However, in Drosophila paulistorum there is information suggesting that if Y chromosome and cytoplasm are from different parents, the male is usually sterile. ( Perez-Salas & Ehrman 1971 ) X-Y interactions are the most likely cause of sterility in male hybrids. It has been shown that interbreeding organisms that have more genetic compatibilities have less disruption of spermatogenesis and normal sized testes, while species who are less genetically compatible have a higher disruption in spermatogenesis and generally have atrophied testes. (Reference needed) Another possible cause of sterility among species in which presence or absence of one or the other sex chromosome determines gender, is if one sex chromosome of one species has recessive alleles interacting with autosomal alleles of the mating species. This could cause the heterogametic sex chromosome in the hybrid to be inviable or sterile, but homogametic sex chromosome will be fertile ( Futuyma 1997 ). Consequently, in species where presence or absence of a Y chromosome determines gender, for instance, individuals carrying XY chromosomes (males) will be sterile and those carrying XX (females) will be fertile. This is closely related to Haldane's rule. Experiments have led scientists to believe that many observations recorded in laboratories neglect existing polymorphism factors in hybrid sterility due to crossing parents from non-isofemale lines, as well as possibly underestimating actual degrees of sterility caused by inaccurate measures of motility. (Reference needed) Failure to account for potential polymorphism could lead to misinterpretation of the scale on which hybrid sterility occurs.
Working in the early 20th century T.H. Morgan, was the first to use Drosophila to explore heredity. Primarily on the basis of work with D. melanogaster, Morgan and his colleagues C.B. Bridges, A.H. Sturtevant, and H.J. Mueller developed a chromosome theory of heredity, for which Morgan was awarded a Nobel Prize in 1933. Their experiments consisted of cross-breeding Drosophila mutants and documenting offspring. Another highly regarded figure in Drosophila research was Theodosius Dobzhansky, who invented the use of genetic markers and used them to study hybrid sterility between Drosophila pseudoobscura and Drosophila persimilis . Futuyma 1997 This experimental method has been used for many years. Experiments involving crosses between D. pseudoananassae and D. bipectinata, D. pseudoananassae and D. parabipectinata, and D. pseudoananassae and D. malerkotliana have further shown that the Y chromosome has a role in hybrid male sterility. The possible interactions of Y chromosome are X-Y, Y-autosome and Y-cytoplasm . Paras 2006 The sterile males carry a set of conspecific autosomes to the Y chromosome, which results in fertility because of the Y-dominant autosome interactions. Therefore, Y-autosome interactions are ruled out in this type of hybrid sterility. Since cytoplasmic factors can be compatible between these species , such factors are also dismissed as the cause of sterility. However, in Drosophila paulistorum there is information suggesting that if Y chromosome and cytoplasm are from different parents, the male is usually sterile. Perez-Salas & Ehrman 1971 X-Y interactions are the most likely cause of sterility in male hybrids. It has been shown that interbreeding organisms that have more genetic compatibilities have less disruption of spermatogenesis and normal sized testes, while species who are less genetically compatible have a higher disruption in spermatogenesis and generally have atrophied testes. Another possible cause of sterility among species in which presence or absence of one or the other sex chromosome determines gender, is if one sex chromosome of one species has recessive alleles interacting with autosomal alleles of the mating species. This could cause the heterogametic sex chromosome in the hybrid to be inviable or sterile, but homogametic sex chromosome will be fertile . Futuyma 1997 Consequently, in species where presence or absence of a Y chromosome determines gender, for instance, individuals carrying XY chromosomes (males) will be sterile and those carrying XX (females) will be fertile. This is closely related to Haldane's rule. Experiments have led scientists to believe that many observations recorded in laboratories neglect existing polymorphism factors in hybrid sterility due to crossing parents from non-isofemale lines, as well as possibly underestimating actual degrees of sterility caused by inaccurate measures of motility. Failure to account for potential polymorphism could lead to misinterpretation of the scale on which hybrid sterility occurs.
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