Medidas de Protección

CONTENTS

1.0 Introduction

2.0 Objective

3.0 Main content

3.1. Polyploidy

3.2. Apomixis

4.0 Conclusion

5.0 Summary

6.0 Tutor Marked Assignment (TMA)

a. What is Polyploidy?

b. What is Apomixis?

7.0 References/Further reading 1.0 Introduction

Polyploidy: multiple sets of chromosomes in an organism (e.g. tetraploid, octaploid). Each set of chromosomes is capable of independent variation: mutation, recombination events.

The resulting organism is in most cases incapable of forming fertile offspring with members of the ancestral diploid population. It has therefore acquired instant reproductive isolation while Apomixis is when the genetic cause of apomixis is identified, apomixis could be applied to plant breeding programs as a means of permanently fixing hybrid vigor, or immediately capturing desirable genotypes.

2.0 Objective: At the end of the class, student s must be familiar and must have understood effectively that polyploidy is the multiplication of the chromosome set or genome and apomixis is the replacement of sexual by asexual reproduction.

3.0 Main content

3.1. Polyploidy

Polyploidy: multiple sets of chromosomes in an organism (e.g. tetraploid, octaploid). Each set of chromosomes is capable of independent variation: mutation, recombination events.

The resulting organism is in most cases incapable of forming fertile offspring with members of the ancestral diploid population.

It has therefore acquired instant reproductive isolation. If it is capable of reproducing, and finding an ecological niche it can exploit, a new species has been formed. Example: In the foxtail species-group: ancestral diploid green foxtail hypothesized to have hybridized with unknown Setaria sp., resulting progeny were fertile, polyploid, and gave rise to yellow and giant foxtail (both polyploid), which subsequently found niche not fully exploited by green foxtail

3.2. Apomixis

Apomixis is found in over 300 species of at least 35 different plant families (Bashaw &

Hanna, 1990). Scientists and geneticists have studied the two broad categories of apomixis—gametophytic and sporophytic—because of their widespread occurrence and potential usefulness in plant breeding. The genetic analysis of apomixis provides

researchers with unique obstacles because of ploidy levels, lack of sexual progeny, lethality, and accurate identification and classification of progeny.

Methods of accurately classifying progeny in genetic studies are being identified and currently several methods are available to researchers, none of which provide a complete picture. These include phenotypic analysis, cytoembryological study, methods, and a variety of markers. A combination of these methods may be used to accurately classify progeny.

When the genetic cause of apomixis is identified, apomixis could be applied to plant

breeding programs as a means of permanently fixing hybrid vigor, or immediately capturing desirable genotypes. Several theories of the genetic control of apomixis have been put forth.

Studies suggest one major gene or linkage group with the possibility of modifying genes.

None of the theories have been proven to be completely satisfactory due to the lack of inheritance data, inaccurate progeny classification, and recombination.

4.0 Conclusion

Polyploidy: multiple sets of chromosomes in an organism (e.g. tetraploid, octaploid). Each set of chromosomes is capable of independent variation: mutation, recombination events.

The resulting organism is in most cases incapable of forming fertile offspring with members of the ancestral diploid population.It has therefore acquired instant reproductive isolation. If it is capable of reproducing, and finding an ecological niche it can exploit, a new species has been formed. Example: In the foxtail species-group: ancestral diploid green foxtail hypothesized to have hybridized with unknown Setaria sp., resulting progeny were fertile, polyploid, and gave rise to yellow and giant foxtail (both polyploid), which subsequently found niche not fully exploited by green foxtail. Apomixis is found in over 300 species of at least 35 different plant families (Bashaw & Hanna, 1990). Scientists and geneticists have studied the two broad categories of apomixis—gametophytic and sporophytic—because of their widespread occurrence and potential usefulness in plant breeding. The genetic analysis of apomixis provides researchers with unique obstacles because of ploidy levels, lack of sexual progeny, lethality, and accurate identification and classification of progeny.

Methods of accurately classifying progeny in genetic studies are being identified and currently several methods are available to researchers, none of which provide a complete picture. These include phenotypic analysis, cytoembryological study, methods, and a variety of markers. A combination of these methods may be used to accurately classify progeny.

When the genetic cause of apomixis is identified, apomixis could be applied to plant

breeding programs as a means of permanently fixing hybrid vigor, or immediately capturing desirable genotypes. Several theories of the genetic control of apomixis have been put forth.

Studies suggest one major gene or linkage group with the possibility of modifying genes.

None of the theories have been proven to be completely satisfactory due to the lack of inheritance data, inaccurate progeny classification, and recombination.

5.0 Summary

Polyploidy: multiple sets of chromosomes in an organism (e.g. tetraploid, octaploid). Each set of chromosomes is capable of independent variation: mutation, recombination events.

The resulting organism is in most cases incapable of forming fertile offspring with members of the ancestral diploid population. It has therefore acquired instant reproductive isolation while Apomixis is when the genetic cause of apomixis is identified, apomixis could be applied to plant breeding programs as a means of permanently fixing hybrid vigor, or immediately capturing desirable genotypes

6.0 Tutor Marked Assignment (TMA) a. What is Polyploidy?

b. What is Apomixis?

7.0 References/Further reading

 Core, E.L.(1955). Plant Taxonomy, Prentice-Hall, Englewood Cliffs, N.J., Pp. 9-61. (An excellent history of plant taxonomy).

Hutchinson, J.(1969). Evolution and Phylogeny of Flowering plants, Academic Press, London, 400pp.

Bessey, C.E.(1915). Phylogenetic Taxonomy of Flowering Plants, Ann. Mo. Bot.

Gard., 2: 109-164.

Gardner, E.J. (1972). History of Biology, 3ed., Burgess, Mineapolis.

Samuel, B.J. and Arlene, B.L. (1986). Plant Systematics. McGraw-Hill, Inc, San- Francisco. 512pp.

Unit 4: Specimen Preparation and Herbarium Management I