Transcript From out of old fields comes all this new corn:

Plant breeding and
Biologia fiorale
genetics
Stimma
Ovario
Nettari
Antere
Petali
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Eredità Mendeliana
• 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
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Accoppiamento
B
A
Segregazione
b
a
b
B
A
a
A
b
a
Assortimento
Indipendente
B
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Che cosa è il genotipo
della F1 ?
Come segregherà nella
generazione F2 ?
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X
Green, round
yy RR
Yellow, wrinkled
YY rr
Cosa sono i genotipi
e i fenotipi delle
generazioni F1 ed F2 ?
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Eredità Mendeliana
• Risultati di incroci di pisello con parentali che differiscono per 1
carattere
• Prima legge : la segregazione
Fenotipo parentali
F1
F2
F2 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
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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
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Scopi dell’inbreeding
• Mantenimento di specifici genotipi
3n genotipi
2n genotipi
n = no. of genes
ex: AA, Aa, aa
• Selezione contro i recessivi
AA , aa
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Outcrossing
• Incrocio causale – promuove la diversità
• Eterozigosità
• L’esempio estremo è l’ibrido F1 (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
S1S3
S1S3
NO
NO
S1S2
S2S3
Incompatibile
Incompatibile
S1S3
S2S4
Compatibile
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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
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Inheritance of Male Sterility
• Genic
• msms = sterile
• msms X MsMs
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
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Use of Genic Male Sterility
Fertile parent MsMs
msms x MsMs
Msms
Segregate 3:1, 25% sterile
PROBLEM IS - HOW DO YOU
IDENTIFY and maintain msms
steriles ?
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Use of Cytoplasmic Male Sterility
• Must use sterile as female parent,
• all progeny are sterile
SXF
S
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Use of Cytoplasmic-Genic Sterility
• Inheritance of CMS system
Smsms x Nmsms
Smsms only, all sterile
Smsms x NMsMs
SMsms only, all fertile
SMsms x NMsms
1 Smsms sterile
2 SMsms fertile
1 SMsMs 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 2n
•Base number of chromosomes (one of each
pair) is ‘x’
•If 2n=2x=22, gametes are n=x=11 (diploid)
•If 2n=4x=44, gametes are n=2x=22 (autotetraploid)
•In a monoploid, 2n=x=11
•In a triploid, 2n=3x=33
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Ploidy Configuration
Haploid
1x
Triploid
3x
Diploid
2x
Tetraploid
4x
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Autoploidy
•Monoploid
A
•Diploid
AA
•Triploid
AAA
•TetraploidAAAA
•Pentaploid
AAAAA
•Hexaploid
AAAAAA
•Duplication: 2n=2x...........2n=4x
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Genetics of Autoploidy
•Autotetraploid: 5 different genotypes
•Gametes are 2x
•Nulliplex
•Simplex
•Duplex
•Triplex
•Quadriplex
aaaa
Aaaa
AAaa
AAAa
AAAA
Banana
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• Banana typically autotriploid and sterile
• Low fertility is desired to make a seedless banana
• Fruit is produced parthenocarpically
Allopolyploidy
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•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
AABB
AABBC
AABBCC
allopolyploidy
A
B
D
Separate genomes come together, but each
Genome has normal diploid pairing and
segregation
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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
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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
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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.
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Yellow butternut
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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 aaBB
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Pedigree selection
Implementation
P1 AAbb
x
F1 AaBb
P2 aaBB
F2 (9 genotypic classes) 3n
A_B_
AAB_
A_BB
aabb
F (4 genotypic classes) 2n
AABB AAbb
aaBB aabb
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Pedigree selection
Implementation
• Self pollinate each F2 plant, and grow out F3
families. Self pollinate selected plants.
– Select among and within families in early
generations
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Pedigree selection
F2 plants
1/4
BB
1/2
Bb
1/4
bb
Individuals
F3
Families
BB
BB
BB
BB
BB
Bb
Bb
bb
BB
Bb
Bb
bb
bb
bb
bb
bb
Pedigree selection
Outline
F1
F2
individuals
Select
among
F3
Select
Families among and
within
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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
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Negative features
• Maximum productivity is established in F2
generations.
– From AaBbCcdd cannot select AABBCCDD
• Minimum recombination
– No opportunities to cross
aabbCCDD x AABBccdd