1. 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

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

3. 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

4. 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

5. 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

6. 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

9. 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

15. 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

17. 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

18. 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

19. 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

20. 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