Types of variation among plants

Presentation on theme: "Types of variation among plants"— Presentation transcript:

1 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

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

3 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

4 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

5 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

6 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

7 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

8 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

9 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

10 Concept of a population and gene pool
Plant Breeding 2009 Fall Concept of a population and gene pool Breeding methods focus on individual plant improvement? or focus on improving populations? -Plant pop. impact their genetic structure -Genetic structure determins its capacity to be changed by selection -Understanding population structure is key to deciding the plant breeding options and selection strategies. Population : a group of sexually interbreeding individuals Capacity to interbreed implies that every gene within the group is accessible to al members through the sexual process. Chapter 2

11 Concept of a population and gene pool
Plant Breeding 2009 Fall Concept of a population and gene pool Gene pool: total number and variety of genes and alleles in a sexually reproducing pop. that are available for transmission to the next generation. Pop. genetics: how the frequencies of alleles in a gene pool change over time To understand population structure and its importance to plant breeding, it si important to understand, - the type of variability present - underlying genetic control - mode of selection for changing the genetic structure Chapter 2

12 Mathematical model of a gene pool
Plant Breeding 2009 Fall Mathematical model of a gene pool The genetic properties(structures) of a pop. are influenced in the process of transmission of gene from one generation to the next by four major factors Population size Differences in fertility and viability Migration and mutation Mating system Population genetics uses mathmetical models to attempt to describe population phenomena (like changes in gene frequency) Chapter 2

13 Mathematical model of a gene pool
Plant Breeding 2009 Fall Mathematical model of a gene pool Calculating gene frequency Conditions.. A large pop. in which random mating occures No mutation or gene flow between this pop. and others No selective adventage for any genotype Normal meiosis One locus (A) with two allele (A, a) (diploid) (2D+H)/2N = (D+1/2H)/N= p, q = 1 - p p = frequency of A allele, q = frequency of a allele D = AA, H = Aa, N= no. of individual Chapter 2

14 Mathematical model of a gene pool
Plant Breeding 2009 Fall Mathematical model of a gene pool The frequency of AA = p2 The frequency of Aa = 2pq The frequency of aa = q2, and then p2 + 2pq + q2 = 1 -> Hardy-Weinberg equilibrium (bewteen genes and genotype) If N=80, D=4, H=24, calculate the genotype frequencies for the next generation following random mating And calculate the frequencies of the genes in the next generation.. Chapter 2

15 Mathematical model of a gene pool
Plant Breeding 2009 Fall Mathematical model of a gene pool As you calculated, allele freq. remains unchanged, while the genotypic freq. changes.. However, in the subsequent generations, both the genotype and gene freq. will remain unchanged, provided: Random mating occurs in a very large diploid pop. Allele A and allele a are equally fit There is no differential migration of one allele into ot out of the population The mutation rate of allele A is equal to that of allele a -> the variability does not change from one generation to another Chapter 2

16 Mathematical model of a gene pool
Plant Breeding 2009 Fall Mathematical model of a gene pool Hardy-Weinberg equilibrium Chapter 2

17 Mathematical model of a gene pool
Plant Breeding 2009 Fall Mathematical model of a gene pool When the presence of genetic linkage Chapter 2

18 Mathematical model of a gene pool
Plant Breeding 2009 Fall Mathematical model of a gene pool Inbreeding and its implications in plant breeding Chapter 2

19 양적형질 통계 분석  통계량 (평균, 분산, 표준편차, 표준오차)
- 표현형 분산 (phenotype variation, VP) = 유전분산 (genetic variance, VG) + 환경분산 (Environmental variance, VE) - 유전분산 = 상가적 분산 (Additive genetic variance, VD , 고정 가능한 분산) + 우성분산 (Dominance variance, VH) aa Aa AA h -d d

20 양적형질 통계 분석 유전자형 AA Aa aa 유전자형빈도 (fi) ¼ ½ ¼ F2 집단에서 유전분산 및 표현형 분산의 분산성분
VG = (1/2)D + (1/4)H VF2 = (1/2)D + (1/4)H + E  여교배 집단에서 유전분산 및 표현형 분산의 분산성분 VB = (1/2)D + (1/4)H + 2E 유전자형 AA Aa aa 유전자형빈도 (fi) ¼ ½ ¼ 유전자효과 d h d

21 유전력 (Heritability)  후대와 친세대 간의 유사성정도를 나타내는 통계량
 양적형질의 표현형에 작용하는 유전적 요인의 중요성과 친의 특성이 후대로 유전되는 정도를 나타내는 척도  선발육종에서 선발의 난이성과 개량의 정도를 예측하는 지표  넓은 의미의 유전력( broad-sense heritability, hB2) - 전체 표현형 분산(VP)에 대한 유전분산(VG)의 비율 hB2 =(D+H)/(D+H+E)  좁은 의미의 유전력( narrow-sense heritability, hN2) - 전체 표현형 분산(VP)에 대한 상가적 유전분산(VD)의 비율 hN2 =(D)/(D+H+E)

22 Q1. 꽃의 길이가 다른 담배품종 간 교배집단에서 각 세대의 분산은
다음과 같다. 유전력을 구하라 Vp1 = 7.65, Vp2 = 8.53, VF1 = 8.25, VF2 = 40.96 힌트: hB2 =(VF2 -VE) / VF2 Q2. 개화기간이 다른 담배품종 간 교배집단에서 각 세대의 분산은 다음과 같다. 유전력을 구하라 Vp1 = 48, Vp2 = 32, VF1 = 46, VF2 = 130.5, VB1 = 88.5, VB2 = 98.5 힌트: hN2 = [2VF2 - (VB1 +VB2 )] / VF2

23