MINISTRY OF EDUCATION AND SCIENCE OF UKRAINE

NATIONAL AVIATION UNIVERSITY

Institute of ecological safety

DEPARTMENT OF BIOTECHNOLOGY

Homework

Heterosis

Student :Oksana Ivachshenko

Group IES 204

Instructor: Vasylchenko O.A

Kyiv 2013

Contents

1. Introduction

2. Molecular basis of heterosis

3. Animal heterosis

   1. Hybrid livestock

   2. Humans

   3. Plants

      1. Corn (maize)

      2. Rice (Oryza sativa)

4. Practical application of heterosis

   1. Methods of inducing heterosis

      1. Combining ability

      2. Periodic selection

      3. Convergent improvemen

      4. Cumulative selection

      5. Gamete selection

4.2Retention of heterosis

5. Conclusion

References

1. Introduction

The term heterosis (or hybrid vigour) characterizes the increased ability or a hybrid as compared to the parental forms. The term ability means the favourable changes in hybrid characters when compared to the abilities of P (Parental) in one or several characters. This phenomenon was discovered in the 18th century by Veldeiter during experiments on tobacco hybridization and later confirmed by many selectionists working on hybridization of plants and animals. It was noticed that the main value of inbreeding - retention of desired characters - is connected to an equal degree with the risk of their diminution. Darwin (1876) was the first to attempt to explain the theoretical fundamentals of heterosis. He concluded that cross-pollination usually produced a favourable effect, and spontaneous pollination a detrimental one. Darwin's works on comparison of spontaneous pollination and cross-pollinated plants gave rise to many investigations on selection. By the time of the re-discovery of Mendel's laws, considerable practical material was collected which confirmed the conclusion made by Darwin and also the two very important earlier observations made by Kolreuter (1763,1766) (hybrid ability is connected with the degree of genetic difference between their parents; hybrid vigour is of special importance in the process of evolution). [9]

The genetic basis has been discussed for nearly a century but little consensus has emerged. With the advent of the genomic era, the tools to establish a molecular basis for heterosis are at hand. In the past, there has been a tendency to attribute any molecular differences between the parents and progeny as contributing to the basis of heterosis. Some individuals dismiss the phenomenon as hopelessly complex. It seems likely, however, that the complexity derives from its multigenic nature and that eventually a unifying principle will emerge.

At present the phenomenon of hybrid ability has been investigated adequately only from the point of view of application, and no general theory of genetic heterosis has been created. From a number of concepts, two theories have been most successfully developed: dominant linkage factors and super-dominance. There are experimental data in favour of both concepts. However, there are facts which do not completely conform to either of them. Eventually, when a general theory of heterosis is developed, each concept will have its proper place. [7]

The object of research are phenomenon of heterosis , molecular basis of heterosis.

The purpose of the study is to study mechanism and features of heterosis .

Objective: to study and scientific foundation the process of heterosis.