Germplasm Issues Chapter 3. Variation: Type, Origin, and Scale Plant Breeding 2009 Fall Chapter 3. Germplasm Issues Variation: Type, Origin, and Scale Plant Genetic Resources for Plant Breeding Chapter 2

The Art and Science of Plant Breeding Plant Breeding 2009 Fall The Art and Science of Plant Breeding 1) Rules and roles of the plant classification 2) Origin of genetic variation 3) Scale of genetic variation 4) Qualitative and quantitative variation Chapter 2

Types of variation among plants Plant Breeding 2009 Fall Types of variation among plants Two fundamental sources of change in phenotype P = G (genotype) + E (environment) Environmental variation Plants exhibit differences in the expression of some traits by non-uniform environments Clones may perform differently under different environments Inferior genotypes can outperform superior genotypes under uneven environmental conditions Plant breeders use statistical tools and other selection aids to reduce the selection errors Chapter 2

Types of variation among plants Plant Breeding 2009 Fall Types of variation among plants Two fundamental sources of change in phenotype P = G (genotype) + E (environment) Genetic variability Genetic variability is consistently expressed generation after generation -> heritable variation Breeders seek to change the phenotype permanetly and heritably by changing the genotypes that encode it Biotechnological tool (DNA markers) allows to access genetic diversity at the molecular level Chapter 2

Origin of genetic variability Plant Breeding 2009 Fall Origin of genetic variability Genetic recombination -applies only to sexually reproducing species -represents the primary source of variability -occurs via the cellular process of meiosis - Creation of non-parental types in the progeny of a cross, through the physical exchange of parts of homologous chromosomes -include only genes that are present in the parents -no genetic linkage => new genetic recombination is predictable Presence of genetic linkage => the frequency of genetic recombination is estimated based on the distance between gene loci on the chromosomes at the molecular level Chapter 2

Origin of genetic variability Plant Breeding 2009 Fall Origin of genetic variability Ploidy modifications Modifications in chromosome number as a result of hybridization between unidentical genotypes or abnormalities in the nuclear division processes Polyploid: individuals with multiples of the basic set of chromosomes) Aneuploidy: individuals with multiples of only certain chromosmes or deficiencies of others Chapter 2

Origin of genetic variability Plant Breeding 2009 Fall Origin of genetic variability Mutation Important in biological evolution as sources of heritable variation Spontaneously arise in nature as a result of errors in DNA replication and by chromosomal aberrations (deletion, duplication, inversion, translocation) The molecular basis of mutation Modification of the structure of DNA Base substitution Base deletion/addition -can be induced by breeders using irradiation/chemical -may useful, deleterious, or neutral Chapter 2

Origin of genetic variability Plant Breeding 2009 Fall Origin of genetic variability Transposable elements = transposons = jumping gene Genes with the capacity to relocate within the genome (transposition) Barbara McClintock, corn in 1940, spots of pigment in the kernel=genetic mosaicism Dissociation(Ds, autonomous element) and activator(Ac, non-autonomous) system (Ds-Ac system) Chapter 2

Scale of variability Qualitative variation Plant Breeding 2009 Fall Scale of variability Qualitative variation categorized by counting and arranging into distinct non-overlapping groups (=discrete variation) Easy to classify, study, and utilizes in breeding Controlled by one or a few genes and inherited simply Amenable to Mendelian analysis Transfer of single gene in GMO (Bt, Ht resistance) Breeding qualitative traits is straightforward Single gene vs. multiple gene Dominant gene vs. recessive gene Chapter 2

Scale of variability Qualitative variation Plant Breeding 2009 Fall Scale of variability Qualitative variation categorized by counting and arranging into distinct non-overlapping groups (=discrete variation) Easy to classify, study, and utilizes in breeding Controlled by one or a few genes and inherited simply Amenable to Mendelian analysis Transfer of single gene in GMO (Bt, Ht resistance) Breeding qualitative traits is straightforward Single gene vs. multiple gene Dominant gene vs. recessive gene Chapter 2

Scale of variability Quantitative variation Plant Breeding 2009 Fall Scale of variability Quantitative variation occur ona continuum and cannot be placed into discrete groups by counting Intermadiates exist between the extreme expressions Controlled by many to numerous genes (polygenic) with effects that are too small to be individually distinguised Minor gene vs. major gene -trait expression is very significantly modified by the variation in environmental factos -Breeding is more challenging Chapter 2

유전자 발현에 미치는 환경적 영향: 표현형 = 유전형 + 환경. 형질에 따라 환경의 영향 정도가 Plant Breeding 2009 Fall 유전자 발현에 미치는 환경적 영향: 표현형 = 유전형 + 환경. 형질에 따라 환경의 영향 정도가 다름. (a) 환경적 영향이 약하며 두 부모본의 형질이 F2 집단에서 쉽게 관찰됨. (b) 환경적 영향이 강하며 분리집단에서 표현형의 차이가 연속적이고 뚜렷하지 않음 Chapter 2