Taxonomic Information from Breeding System Class MS Semester

Taxonomic Information from Breeding System Class MS Semester II Course Title: Molecular Advances in Phytosystematics Instructor: Dr. ARUSA AFTAB DEPARTMENT OF BOTANT LAHORE COLLEGE FOR WOMEN UNIVERSITY LAHORE

Taxonomic information from breeding system Breeding system: “who mates with whom”. • Include variety of ways through which plants reproduce • Specific characters of plant can be studied • Similarities and differences among similar and different plants are observed. http: //https: //www. encyclopedia. com/science/news-wires-white-papers-andbooks/breeding-systems

Plant Breeding: “The science of changing traits of plants to produce desired characteristics. ” Breeding can be accomplished through different techniques ranging from • Propagation methods: simply select plants with desirable characters • Molecular techniques: use the knowledge of genetics and chromosomes. Breeders strive to create; i. Specific outcome ii. New plant varieties

Breeding systems: A. Apomixis: any form of asexual reproduction • Vegetative apomixis; veg. reproduction (rhizomes, stems, stolons • Agamospermy; seeds produce without fertilization (e. g. , Erigeron annuus) B. Self fertilization • Cleistogamous flower; flowers that do not open to expose rep. organs thus prevent cross-pollination C. Obligate outbreeding • Temporal and structural differences e. g. , heteromorphic flowers and protandry or protogyny. http: //https: //www. docsity. com/en/breeding-systems-plant-taxonomy-andsystematics-lecture-notes/237253/

Ideal species: “A model organism that usually possess a specific trait that makes them easier to use in experimental set-ups” • Easy to cultivate e. g. , maize • Also called model species or so called exemplar taxa • Particular phenotype can produces through selective breeding • Can produce different varieties • Should easy to find and identify • Should less affected by anthropogenic activities. http: //https: //www. researchgate. net/post/Which_general_traits_define_an_ideal _species_group_as_model_in_ecological_studies

Hybridized specie: “hybridization between two different species leads to a new species i. e. , reproductively isolated. ” Mostly Polyphyletic in nature. These species can be result of: • Natural hybridization • Artificial hybridization (selective breeding) Hybrid are not always intermediate between their parents due to • Hybrid vigor: grow larger than either parents • Barriers: genetics, morphological differences, mating behaviors, fertility times etc.

Genetics of hybridizing species: Many agriculture crops are hybrids with double or even triple chromosome sets. Other forms of hybrid are • Polyploidy: having multiple chromosome sets • An infertile hybrid becomes fertile by doubling the chromosome • Homoploidy: without any change in chromosome number (mostly in animals) http: //https: //en. m. wikipedia. org/wiki/Selective_breeding http: //https: //en. m. wikipedia. org/wiki/Hybrid_(biology)

Extent of hybrid species: The extent to which natural hybridization contributes to evolution is wide ranging. The hybridization between species can result in • Total breakdown of species barriers • Homogenize parental genome • Formation of stable hybrid zones • Novel gene combinations in hybrids • Evolutionary responses and local adaptations • Formation of new species. http: //https: //www. researchgate. net/publication/327507466_Incomplete_reproductive_isolation_ between_Rhododendron_taxa_enables_hybrid_formation_and_persistence_Weak_reproductive_is olation_promotes_hybridization_in_Rhododendron

Recognition of hybrid species: Whenever hybridization is common between taxa, the resulting crosses will have impact on species characters (fertility, weight) and even fossil records. The hybrid species can be identified by: • Total genetic distance is the primary determinant of species status. • Reproductive isolation- the conflict between hybrid species and biological species concept is reproductive isolation as main criteria for taxa separation • An approach to identify sequence of multiple genes, representative collections and the exclusion of hypothesis to describe variations in hybrids.

Recognition: The treatment of hybrid in terms of nomenclature is highly depend upon : “ 120 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON”. Hybrids are not seen as problem to phylogenetic species. At present, the genus Lasiodiploida comprises 31 hybrid species out of 20 which are mostly distinguished by using the sequence of gene and PCR amplification. Cryptic lineages resolved the taxonomy of the species and defined them as distinct species including hybrid species. http: //https: //www. ncbi. nlm. nih. gov/m/pubmed/28317543

Consequences of hybrids: Hybrid fitness is difficult to predict because the mixing of gene pools can • Simultaneously create both beneficial and detrimental gene interactions • These interactions can change substantially between generations due to recombination. Crosses can result in • Increase in fitness • Decrease in fitness

Increase in fitness: • Mask the deleterious recessives – over dominanace • Epistasis can be involved • Also called hybrid vigor or heterosis. Decrease in fitness: • Disrupt local adaption • Underdominance or epistatic interactions • Also known as outbreeding depression or hybrid breakdown • Can occur in first (F 1) generation or fitness declines are delayed until second generation (F 2). http: //www. biodiversity-science. net/EN/10. 17520/biods. 2003041

Outbreeding depression: Hybridization is common in nature and widely used in agriculture to create new breeds but its harmful consequences can not be neglected as they • Broken adaptive gene complexes in one species due to immigration • Lower future species fitness by causing mal-adaptation • No genetically “pure” progeny will produced • They may gain resistance to disease thus becoming more difficult to control. http: //https: //academic. oup. com/jhered/article/96/2/114/2187513

Stabilization of hybrids: Hybrids can have less fitness, more fitness or the same fitness level as the purebred parents. Usually they tend to be less fit • Therefore reproduction to produce hybrid will diminish over time. • Two species diverge further through reinforcement because low success of hybrids reinforce original species • Reinforcement will occur until the species can no longer produce viable offspring.

Reinforcement: It is the process by which • Natural selection increases reproductive isolation • Hybrid zone develop into a full species barrier • Stability is managed in hybrid zone. http: //https: //www. blackwellpublishing. com/ridley/az/Reinforcement. asp

Fit hybrids: If the hybrids are as fit or more fit than the parents • Reproductive barriers weaken • Two species fuse back into one (reconnection) • A persist hybrid form is stabilized that exploit the available resources better than either parent species.

Hybrid- speciation It is the process through which hybrid themselves can become a separate species. Hybrid species were thought to be rare due to reproductive isolation between parents and hybrids With DNA analysis becoming more accessible in the 1990’s, hybrid speciation has been shown to be a fairly common phenomenon in plants.

Sometimes two species will remain separate but continue to interact to produce some hybrid individuals. This is classified as stability because no net change take place. q. For a hybrid zone to be stable, the offspring produced by the hybrids have to be less fit than members of the parent species. http: //https: //courses. lumenlearning. com/boundlessbiology/chapter/hybrid-zones-and-rates-of-speciation/