Plant breeding and Biologia fiorale genetics Stimma Ovario
Plant breeding and Biologia fiorale genetics Stimma Ovario Nettari Antere Petali 1
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Eredità Mendeliana 3 • La prima legge di Mendel – segregazione – è il risultato diretto della separazione degli omologhi in cellule distinte durante la prima divisione meiotica • La seconda legge di Mendel – assortimento independente – deriva dalla separazione indipendente di differenti coppie di alleli su cromosomi omologhi
Eredità Mendeliana A B a b 4 Accoppiamento B A Segregazione b a b B A a A b a Assortimento Indipendente B
5 Che cosa è il genotipo della F 1 ? Come segregherà nella generazione F 2 ?
6 X Green, round yy RR Yellow, wrinkled YY rr Cosa sono i genotipi e i fenotipi delle generazioni F 1 ed F 2 ?
Eredità Mendeliana 7 • Risultati di incroci di pisello con parentali che differiscono per 1 carattere • Prima legge : la segregazione Fenotipo parentali F 1 F 2 Ratio Round/wrinkled round 5474: 1850 2. 96: 1 Yellow/green yellow 6022 -2001 3. 01: 1 Purple/white purple 705: 224 3. 15: 1 Inflated/pinched inflated 882: 299 2. 95: 1 Axial/terminal axial 651: 207 3. 14: 1 Long/short long 787: 277 2. 84: 1
8 Inbreeding • L’Inbreeding è dovuto all’incrocio tra individui molto imparentati grazie ad un comune genitore ancestrale e sono individui presi a caso dalla popolazione • La sua estrema espressione è il selfing
9 Scopi dell’inbreeding • Mantenimento di specifici genotipi 3 n genotipi 2 n genotipi n = no. of genes ex: AA, Aa, aa • Selezione contro i recessivi AA , aa
10 Outcrossing • Incrocio causale – promuove la diversità • Eterozigosità • L’esempio estremo è l’ibrido F 1 (Aa)
Auto-Incompatibilità • Rinvenuta in molte specie, inclusa la Brassica spp. • Il locus S è Multiallelico (> 60 alleli !) • Tutti i pollini di una pianta hanno la stessa reazione di incompatibilità S 1 S 3 NO NO S 1 S 2 S 2 S 3 Incompatibile S 1 S 3 S 2 S 4 Compatibile 11
Male Sterility Systems • Genic • Nuclear gene conditions sterility • Sterility usually recessive, often msms • Cytoplasmic • Non-nuclear genes responsible for sterility • Pollen parent has no influence on fertility or sterility • Not useful for seed crops • Cytoplasmic-Genic • Non-nuclear genes cause sterility, nuclear restores fertility • Two-gene system required for sterility / fertility • Useful for seed-propagated crops 12
13 Inheritance of Male Sterility • Genic • msms = sterile • msms X Ms. Ms All Msms; 100% fertile • Msms X Msms 3: 1 segregation; 25% sterile • msms X Msms 1: 1 segregation; 50% fertile • Cytoplasmic • SXF All progeny sterile due to maternal inheritance • Cytoplasmic-Genic • Smsms = sterile Only Smsms conditions sterility • NMSMS = fertile Fertility with either N cytoplasm or dominant • Nmsms = fertile Alleles at nuclear restorer locus (Ms) • SMsms = fertile
Use of Genic Male Sterility Fertile parent Ms. Ms msms x Ms. Ms Msms Segregate 3: 1, 25% sterile PROBLEM IS - HOW DO YOU IDENTIFY and maintain msms steriles ? 14
15 Use of Cytoplasmic Male Sterility • Must use sterile as female parent, • all progeny are sterile SXF S
16 Use of Cytoplasmic-Genic Sterility • Inheritance of CMS system Smsms x Nmsms Smsms only, all sterile Smsms x NMs. Ms SMsms only, all fertile SMsms x NMsms 1 Smsms sterile 2 SMsms fertile 1 SMs. Ms fertile S msms F Ms- msms S N F Ms- S F N
Variation in ploidy General concepts: • Genome is basic unit of chromosomal makeup • Chromosomes of a genome inherited together in a ‘normal’ meiosis and mitosis • Chromosome number of the gametophyte is ‘n’ • Chromosome number of the sporophyte is 2 n • Base number of chromosomes (one of each pair) is ‘x’ • If 2 n=2 x=22, gametes are n=x=11 (diploid) • If 2 n=4 x=44, gametes are n=2 x=22 (autotetraploid) • In a monoploid, 2 n=x=11 • In a triploid, 2 n=3 x=33 17
Ploidy Configuration Haploid 1 x Triploid 3 x Diploid 2 x Tetraploid 4 x 18
Autoploidy • Monoploid • Diploid • Triploid • Tetraploid • Pentaploid • Hexaploid A AA AAAAAA • Duplication: 2 n=2 x. . . 2 n=4 x 19
20 Genetics of Autoploidy • Autotetraploid: 5 different genotypes • Gametes are 2 x • Nulliplex • Simplex • Duplex • Triplex • Quadriplex aaaa AAaa AAAA
Banana 21 • Banana typically autotriploid and sterile • Low fertility is desired to make a seedless banana • Fruit is produced parthenocarpically
Allopolyploidy 22 • Typical diploid inheritance patterns because of lack of pairing of chromosome sets • Possibility of multiple alleles in different genomes • Can result in unique nuclear-cytoplasmic interactions • Case of cotton demonstrates value of D genome to cultivated types despite poor performance of D genome per se • Dihaploid • Allotriploid • Allotetraploid • Allopentaploid • Allohexaploid AB ABC, AAB, ABB AABBCC
allopolyploidy A B D Separate genomes come together, but each Genome has normal diploid pairing and segregation 23
24 Triangle of U B. rapa n=10 AA B. juncea n=18 AABB B. nigra n=8 BB B. carinata n=17 BBCC B. napus n=19 AACC B. oleracea n=9 CC
Brasscia oleracea and rapa 25
26 Quantitative inheritance • Quantitative traits – Continuos variation (normal distributions) – Often characterized as being affected by many genes expression of which is modified by the environment • Qualitative traits – Often single gene Mendelian traits – Segregate into discrete classes
Distribution of Quantitative trait(s) * Mean * Variance * covariance 27
Pedigree selection How to do it • Pedigree, as the name implies, provides a record of the lines of descent of all individuals in each generation. • The accumulation of information is important when decisions need to be made regarding keeping or eliminating a line. 28
Yellow butternut 29
Pedigree selection Requirements • Two parents – Choice of parents is critical, as you invest a lot of time and resources in each pedigree pop’n – Complementary in strengths and weaknesses AAbb x aa. BB 30
Pedigree selection Implementation P 1 AAbb x F 1 Aa. Bb P 2 aa. BB F 2 (9 genotypic classes) 3 n A_B_ AAB_ A_BB aabb F (4 genotypic classes) 2 n AABB AAbb aa. BB aabb 31
Pedigree selection Implementation • Self pollinate each F 2 plant, and grow out F 3 families. Self pollinate selected plants. – Select among and within families in early generations 32
33 Pedigree selection F 2 plants 1/4 BB 1/2 Bb 1/4 bb Individuals F 3 Families BB BB BB Bb Bb bb bb bb
Pedigree selection Outline F 1 F 2 individuals Select among F 3 Select Families among and within 34
35 Features of Pedigree selection • After inbreeding and testing lines can be bulked and released as cultivars. • Its fun and flexible • When a superior family is identified, you can trace back in the pedigree and select in earlier generations
36 Negative features • Maximum productivity is established in F 2 generations. – From Aa. Bb. Ccdd cannot select AABBCCDD • Minimum recombination – No opportunities to cross aabb. CCDD x AABBccdd
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