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The Green Planet > Plant Breeding & Genetic Modification > Flashcards

Plant Breeding & Genetic Modification Flashcards

1
Q

Where have recent yield increases come from?

A

Breeding improved crops
Better agronomy (knowledge, pesticides, fungicides, herbicides, machanisation, irrigation)
Increased due to globalisation as more crops can be grown in optimal conditions and im/exported

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2
Q

Why is the yield increase higher for elite varieties compared to landrace varieties when synthetic fertilisers are added?

A

Elite crops have been bred specifically for high input from fertilisers

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3
Q

What is water deficit?

A

More water being used than is sustainable :((

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4
Q

What is the process for making nitrogen fertiliser?

A

Haber-Bosch process

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5
Q

Environmental effects of Haber Bosch process?

A

Consumes lots of energy in form of natural gas
Responsible for 2% of man made emissions
Cost of fertiliser tied to energy costs
N fertiliser ends up as atmospheric NO and N2O due to denirtifying bacteria in the soil - potent greenhouse gases

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6
Q

Why is phosphate fertiliser a finite resource?

A

Mined as rock phosphate from ancient lake sediment or volcanic deposits
Reserves set to be exhausted within 70 odd years at current rate
Patchy global distribution (none in Western Europe D:)

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7
Q

How do livestock produce greenhouse gases?

A

Bacteria in ruminant digestive systems produce CH4

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8
Q

What are the two types of crops cultivated in different parts of the world?

A

One carb rich and one protein rich crop cultivated in each part

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9
Q

Difference between breeding and propagation?

A

Breeding creates cultivars with novel gene combinations, requires sexual reproduction
Propagation creates genetically uniform seeds or plants for growing, can involve sexual or vegetative reproduction

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10
Q

Difference between annuals and perennials?

A

Annuals are seed propagated; must be true-breeding (genetically uniform).
Harvested within 12 months. Includes all main grain crops

Perennials are vegetatively (clonally) propagated. Grown for >1 year, usually harvested many times (except tubers which are planted every year)

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11
Q

How do you make a crop True-breeding?

A

True breeding is homozygous, no segregation.
After about 16 generations of inbreeding, number of heterozygous genes is insignificant
50% of heterozygotes lost each generation

Another method is to culture sterile haploid plants from pollen cells and replicate their genome to restore fertility. Though does require high tech sterile environment

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12
Q

Advantage of vegetative reproduction in nature?

A

Population increase w/out risks of sex

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13
Q

Methods to propagate vegetatively?

A

Runners (strawberry): plant grows out a runner which takes root in another location and another plant grows, eventually connection between mother and daughter withers

Banana corms contain meristems and so can grow whole new plant

Seed potatoes, tubers are modified shoots

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14
Q

What is grafting?

A

Scion of one plant is grafted on to the rootstock of another plant.
Scion provides fruit, determines flowering time
Rootstock provides support, determines size, soil type, time to maturity, resistance to parasites,

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15
Q

How are rootstocks propagated?

A

Vegetatively from cuttings

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16
Q

Solutions for quickly making parasite resistance?

A

Graft onto resistant rootstock
Hybridise with resistant close relative and select resistant hybrids

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17
Q

Advantages and disadvantages of clonal propagation?

A

Offspring are identical
Uniformity in crops without inbreeding program, doesn’t matter if they’re heterozygous

Though all plants will be susceptible to the same diseases (eg bananas, 80% propagated vegetatively)

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18
Q

How does vegetative reproduction increase viral infection

A

Most viruses don’t infect meristems where flowers and seeds are produced so viruses aren’t spread through those.
Previous generation viruses can be passed down through vegetative reproduction though, increase viral load each generation, reduce yield quality

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19
Q

Method for improving viral load in vegetatively reproduced potatoes

A

Can culture meristem tissue from potato shoots and culture them to produce plantlets
These then create mini tubers identical to parent but virus free

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20
Q

Why are legumes protein rich?

A

Embryo contains protein produced in cotyledon cells in the embryos protein body

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21
Q

Why can’t you propagate oil palm from cuttings?

A

Only one shoot meristem and don’t branch

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22
Q

Solution to oil palm vegetative propagation?

A

culture meristem tissue
Thought this can potentially introduce variation into the crop and can cause the plant to be sterile and not fruit

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23
Q

What is the afila mutation in peas

A

Mutation in single gene controlling leaf structure
Lower leaflets converted to tendrils
Can hang onto neighbours better to form self supporting mat which is more wind resistant
Doesn’t affect photosynthesis too much

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24
Q

Why is wheat shorter now than in 1700s?

A

Semi dwarf cereal crops are:
More resistant to lodging
More responsive to fertilisers
Higher yield as more production goes to kernels

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25
Q

What mutation causes dwarfing in wheat

A

Rht
Mutation is dominant
Incorporation into all 6 chromosome sets causes increasing dwarfing

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26
Q

Process for crossing wheat?

A

Emasculate mother plant by removing immature anthers to prevent it self pollinating
Bag the emasculated spikes to prevent unwanted pollination while carpels mature
Collect anthers from father and warm them with thumb to cause dehiscence
Transfer pollen to mother
Label, rebag and let kernels mature

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27
Q

How to do a double cross?

A

Cross A and B
Cross C and D
Cross the F1 of each of these
Self pollinate the F2 (final hybrid)

28
Q

What is screened for during wheat breeding programs?

A

1st thing screened for is disease resistance
Most resistant get to self pollinate
Continue to screen within family for: Lodge resistance, mature time, variation in population)
Inbreeding produces more and more uniform crops (aiming for true breeding)
8 crosses only really give one promising line
2-3 years between new varieties made as diseases adapt

29
Q

What is the issue with crop domestication?

A

Domestication and elite breeding (relies on making better combos from existing alleles) reduced the alleles available for breeding, causes a genetic bottleneck as only a subset of a population is chosen for breeding
Many alleles lost :,(

30
Q

What is a yield ceiling?

A

Bottleneck causes a ceiling on optimum allele combinations as allele variety decreases
Yields could possibly drop as pathogens catch up

31
Q

How to break yield ceiling?

A

-increase recombination between existing alleles by: growing more hybrids, or inducing more recombination (in cereals like wheat, large amounts of the genome don’t recombine together, can’t get all good genes together)

-induce more variation: by;
Mutagenesis mutation breeding, mutagenesis induced and hope it introduces beneficial mutation
Alternative is direct genome editing
Or introgressing traits from landraces or wild relatives (genetically messy and time consuming, bad can also carry over

32
Q

Method for telling which genes came from which parent in a hybrid progeny?

A

Marker assisted selection (used when introgressing traits) to see which gene came from where and can select individuals accordingly
Markers on chromosomes of each parent
Markers can be seen via pcr

33
Q

What is GWAS?

A

Genome Wide Association Study
Uses diverse cultivars or landraces
Looks for correlation between phenotype and marker genotype

Works best when:
Variation is limited
The same genes are involved throughout the population
Population structure is low

34
Q

Benefits of Marker assisted selection over GWAS

A

Don’t have to wait for maturity to test them (saves money, labour)
Fewer generations of backcrossing needed (unsure why notes unclear)
Can select target with less of unwanted surrounding chromosome

35
Q

What is a method for avoiding self-pollination?

A

Some individuals just producing pollen and some just fruit.

36
Q

What is hybrid vigour

A

Aka heterosis
The heterozygosity in hybrid F1 makes an individual more vigourous than the parents

37
Q

Hypotheses for cause of heterosis?

A

Dominance hypothesis:
- Deleterious recessive mutations are masked by the dominant allele from other parent

Overdominance hypothesis:
- Having alleles that encode proteins with slightly different activities (E.g. parents that flower either too early or too late; hybrid just right, gets to grow enough before flowering and doesn’t flower too late= more vigourous), or phenotype that is sensitive to gene dosage.

38
Q

Why is maize amenable for F1 hybrid production but not other grain crops?

A

It is monocious
Flowers aren’t hermaphrodite
Can emasculate plants easily by removing top of plant, no longer self pollinated.

39
Q

How did Chinese breeders make their F1 hybrid rice strain sterile?

A

Introduced mutant mitochondria from wild rice which prevents pollen development (cytoplasmic male sterility)
The sterility is only under certain environments so can be on/off when needed

40
Q

How are F1 hybrid lines maintained?

A

They can’t be
Homozygous parent species hybridising creates an identical F1
Breeding F1 hybrids introduces variation (due to their heterozygosity)

41
Q

What are the advantages and disadvantages of the inability to breed F1 hybrids?

A

Disadvantage for grower as they cannot save seed for sowing :(
Advantage to breeder who has a constant market

42
Q

How can heterosis be maintained?

A

Vegetative propagation
-maintains desired gene combination
-indefinitely maintains heterosis

Non sexual seed production (Apomixis)

43
Q

How can polyploidy occur?

A

Failure of anaphase causes separated sister chromatids to end up in the same nucleus
Cell inherits 2x the normal no. of chromosomes

44
Q

How can polyploidy be artificially induced?

A

Colchicine from Colchicum causes de-polymerisation of spindles and prevents them from pulling chromosomes to the end of the cell

45
Q

Why do polyploids have larger fruit/flowers?

A

Polyploid cells have larger chromosomes -> bigger nuclei and bigger cells
Can give larger fruit/flowers

46
Q

Why do odd numbered polyploidy cause sterility?

A

Unlikely to produce gametes with correct chromosome complement.
Eg Triploie genome can pair to give either a Bivalent + a Univalent, or a Trivalent

47
Q

How are triploids used commercially?

A

Bananas are Triploid and so are sterile
They are propagated vegetatively.
-needs a mutation to develop fruit without fertilisation
-makes breeding difficult as you have to trace back to fertile diploid ancestors

48
Q

Why are even numbered polyploids reduced in fertility?

A

During mitosis chromosomes form either:
Two bivalents (success)
One quadrivent
Univalent +trivalent

49
Q

What’s an advantage of even polyploidy?

A

Heterosis can be maintained
In diploid- 50% of heterozygous plants lost each generation
In Tetraploid- progeny inherit different alleles on different chromosomes

50
Q

Allopolyploidy vs autopolyoloidy?

A

Autopolyoloidy- Doubling of genome, occurs due to failed anaphase

Allopolyploidy- occurs after hybridisation of two close species

51
Q

Advantage of Allopolyploidy in fertility of hybrids?

A

Diploid hybrids are usuall infertile as the chromosomes from each parent don’t associate during meiosis
This is solved in Allopolyploidy as each chromosome can pair with its homologue

52
Q

Why is bread wheat hexaploid?

A

Triticum monococcum (wild AA) hybridised with Triticum searsii (wild BB) -> AB
DOUBLING -> AABB before domestication 10k years ago
Triticum tauschii (wild DD) crosses with domestic variety (AABB, Triticum dicoccoides “Emmer”) to produce
Bread wheat, Triticum aestivum AABBDD

53
Q

Examples of synthetic allopolyploids?

A

Raphanobrassica; radish and cabbage 2n=36 (from 2n=18 parents)

Triticale; Durum wheat and Rye
Combines high protein and drought resist of Durum and Lysine rich and good resistance of Rye

54
Q

Advantages and disadvantages of GM?

A

Adv:
Quicker than conventional breeding
Cleaner (only one round for elite crop background, as opposed to many generations of breeding)
Not limited to genes in interfertile relatives
Patentable

Disadv:
Requires knowledge of gene function
Adverse public opinion leads to strict legal regulation

55
Q

Method for reducing expression of a specific gene?

A

Antisense technology:
Insert a gene that is the reverse of a native gene
mRNA strands will be complementary and form dsRNA
Plant has defence mechanisms against virus dsRNA and so chops it up
Reduced production of a specific protein

56
Q

How to inhibit softening in fruit, but not ripening?

A

PolyGalacturonase hydrolyses pectin
Use Antisense technology to knock down PG production
This GM tomato didn’t show any significant difference (rip Flavr Savr)

57
Q

Do I need to make flash cards on flavr savr?

A

Do we really care?

58
Q

What 2 GM traits dominate agriculture?

A

Tolerance to herbicide (mainly roundup)
Bt-mediated insect resistance

59
Q

What is Bt toxin?

A

Cry protein produced by soil bacterium (Bacillus thuringiensis) when it sporulates
Spores and Cry crystals eaten by insect
Cry split by high pH in gut
Binds to receptors in gut cell membrane
Forms a lore complex and punctures membrane
Gut cells die
Insect dies
Becatria eats insect

60
Q

Advantages of Bt toxin

A

Very species specific (gut receptors) no collateral casualties
Is a protein so is digested and doesn’t build up in food chains
Can be integrated into plants to make them genetically insect resistant

(Though it is relatively expensive to produce)

61
Q

What is the typical effect of untreated weeds on crops?

A

A decrease in yield of around 50%
Weeds can also harbour diseases

62
Q

What is an issue posed by herbicides targeted towards a specific plant group?

A

A weed and crop of same type can’t be treated with it (don’t want to kill crop)

63
Q

What is roundup?

A

A glyphosate pesticide
N-phosphonomethyl glycine
Produced by Monsanto
(Originally as water softener but failed toxicology tests)

64
Q

How does roundup/Glyphosate work?

A

Inhibits EPSPS
key enzyme of shikimic acid pathway
Needed to make aromatic amino acids (phenylalanine, tyrosine and tryptophan)
Though this is only in plants bacteria and fungi so low toxicity to animals

65
Q

How to make roundup resistant plants?

A

Isolate agribacterium in waste water
Bacteria have shikimic acid pathway so may develop resistance gene to glyphosate

-isolate gene
-modify for optimal plant expression and target protein to chloroplasts
Introduce into plants

66
Q

What is biofortiifed rice

A

Rice with vitamin a synthesis pathway engineered into it
Synthesis enzymes from more closely related species work better (eg Maize vs daffodil)

The Green Planet (8 decks)

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