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The Green Planet > Sex, Genes and Agriculture (Block 4) > Flashcards

Sex, Genes and Agriculture (Block 4) Flashcards

1
Q

How much has the world population changed in the last 50 years?

A

It has tripled.

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2
Q

How much has the agricultural land per

person changed in the last 50 years?

A

It has halved.

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3
Q

What are the TWO reasons that crop yields have increased dramatically?

A
  1. Half is from breeding improved crop varieties…
  2. And half is from better agronomy (fertilizers, agrochemicals,
    mechanisation)
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4
Q

How can we test the effect of Crop Breeding on yield?

A

We can grow old varieties of crops from seed banks under the same conditions as modern varieties and then compare them.

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5
Q

What does it mean that “Crops have been bred for high inputs”?

A

While modern varieties outperform traditional ones, they often only do so when comparing both crops with high inputs of (e.g.) synthetic fertiliser.

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6
Q

How much of human water use is agricultural?

A

Around 80%.

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7
Q

What environmental problems are there with Nitrogen Fertilisers?

A

They are produced by the Haber Process, which:
> Consumes massive Energy
> Causes 2% of CO2 emissions
> Ties fertiliser costs to Energy prices
and additionally, the can lead to atmospheric NO production.

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8
Q

Why is Phosphate Fertilizer limited resource?

A

It is mined as rock phosphate from ancient sediments (which cannot be replaced).

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9
Q

Why is the increased consumption of animal products a problem?

A

Feeding crops to livestock is inefficient and produces greenhouse gases.

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10
Q

What pressure other than food do maize crops face?

A

Increased Biofuel production.

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11
Q

What are some of the crop Breeding Targets for the 21st Century?

A

Increased resistance to stress (mainly drought and heat).
Increased resistance to pests and pathogens.
Decreased post-harvest losses (≤30%).
Reduced reliance on fertilizers.
More efficient use of water.

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12
Q

What is the difference between breeding and propagation?

A

Breeding is sexual and creates new cultivars, and propagation creates genetically unique individuals (can be sexual or asexual).

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13
Q

What do the top 5 important food crops grown have in common?

A

The top 5 are all carbohydrate-rich staples.

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14
Q

What is special about the top 3 important food crops?

A

> They make up about 1/2 of all food production.

> They are all cereals (members of the grass family).

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15
Q

What are the top 3 important food crops?

A

Maize, Rice and Wheat (in descending order).

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16
Q

How are annual plants usually propagated?

A

By seeds (must be true-breeding).

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17
Q

How are perennial plants usually propagated?

A

Vegitatively (clonally).

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18
Q

What does “true-breeding” mean?

A

Homozygous.

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19
Q

Why should crops be true-breeding?

A

So they will perform similarly and as expected.

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20
Q

What 2 ways could be used to make a heterozygous variety homozygous?

A
  1. Inbreed for several generations; only 50% of progeny will be heterozygous each time.
  2. Make doubled-haploid (DH) lines; culture haploid cells, to haploid plants, then double the chromosome number with colchicen.
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21
Q

What are some methods of Vegetative Propagation?

A

> strawberry “runners”
banana corms
“seed” potatoes
Grafting of apples or grapes

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22
Q

What is the advantage of Grafting as a method of propagation?

A

> The SCION selected determines type and flowering.
The ROOTSTOCK determines size of tree (and suitability to soil type, time to maturity, whether support needed, resistance to wooly aphid).

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23
Q

What are the Pros and Cons of Vegetative Propagation?

A

PRO: Uniform, no need to make true-breeding.

CON: Susceptible to the same pests and diseases (e.g. 80% of bananas are Cavendish, susceptible to
fungal Panama disease).

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24
Q

What are some major oil crops?

A

Oil palm, oilseed rape, sunflower, peanut, cotton.

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25
Q

Why is Oil Palm such a prominant crop?

A

> It has an extremely massive yield

> It is rich in Palmitic Acid, an alternative to hydrogenated oils (trans fats).

26
Q

What problems does Oil Palm cultivation cause?

A

The destruction of rainforests for plantations.

27
Q

How are Oil Palms propagated?

A

They have only one shoot meristem, so meristem cells are cultured & embryo formation induced.

28
Q

Why is modern wheat much shorter than in the past?

A

The Rht (dwarfing) gene has been progressively integrated into all 6 chromosomes.

29
Q

What is the advantage of Semi-dwarf wheat?

A

Semi-dwarf cereals are more resistant to lodging (falling over) and more responsive to N fertilizers.

30
Q

What effect do domestication and elite breeding have on plant genes?

A

It reduces the alleles available for breeding; a Genetic Bottleneck.

31
Q

Why is a Genetic Bottleneck bad for breeding?

A

Elite Breeding relies on making better combinations of existing alleles, so reducing available alleles might slow improvement.

32
Q

What does the concept of a “Yield Ceiling” describe?

A

The idea that we may be running out of alleles from which to make improved combinations, so yield will hit a plateu. It may even decline as pests and pathogens overcome the plants’ resistance.

33
Q

What evidence is there that the “Yield Ceiling” may not occur?

A

The Illinois maize experiment: Maize was selected for high oil content, which has increased steadily over 100 generations and shows no sign of plateu.

34
Q

How could we break the yield cieling?

A
  1. Increase recombination between existing alleles (more recombinations from “cold spots” on the gene).
  2. Introduce more variation.
35
Q

How could we break the yield cieling via (1) increasing recombination?

A

A - Grow more hybrids (higher statistical chance).

B - Induce more recombination (technology not developed yet).

36
Q

How could we break the yield cieling via (2) introducing more variation?

A

A - Mutation breeding.

B - Introgress genes from landrace or wild relative.

37
Q

What are some issues with Gene Introgression as a method of introducing more variation?

A

> Time-consuming.
Genetically messy (other DNA transferred).
Only works for interfertile species.

38
Q

How can Gene Introgression be made more precise and efficient?

A

Marker-assisted selection.

39
Q

How can genes be identified in Marker-Assisted Selection?

A

Correlation between the phenotype and genotype at different positions. Molecular DNA Markers show which genes came from which parent.

GWAS (sequencing) or QTL (Quantitative Trait Loci) mapping.

40
Q

Under what conditions doesn GWAS (Genome-Wide Associatio Study) work best?

A

A - Variation in the population is limited.
B - The same genes are involved throughout the population.
C - Population structure is low.

41
Q

How can Marker-Assisted Selection help speed up Gene Introgression?

A

We can backcross the F1 generation witht the elite variety, select individuals with good alleles (by analysing the markers) and without bad alleles, and repeat this cycle by backcrossing the progeny (5 generations).

42
Q

What are the advantages of speeding up Gene Introgression via Marker-Assisted Selection?

A

> Quicker - No need to grow plants as seed genomes can be sequenced, so less backcrossing needed too.
Cleaner - can select target alleles with minimal surrounding chromosome, as we can see which is which.

43
Q

Give an example of Marker-Assisted Selection.

A

S. pennellii genes were introgressed into an elite tomato cultivar to increase Brix Yield (sugar mass per m).

44
Q

How can the high-labour aspect of phenotyping be overcome?

A

Via “Phenomics” - Automated Phenotyping.

45
Q

How can the Generation Time of plants be overcome when phenotyping?

A

> Shuttle Breeding - Move seeds to different areas when weather changes to make more generations.

> Speed Breeding - Artificially increase day length (blue + red LEDs). Only works for some plants where others experience distress (potato, aubergine).

46
Q

How can barriers of develeoping countries to breeding techniques be overcome?

A

Participatory Breeding - Kirkhouse Trust sequences genomes and provides training to breeders. Focus on locally important legumes.

47
Q

What mechanisms inhibit inbreeding?

A

> Self-incompatibility.

> Separate sexes.

48
Q

What is the advantage of outbreeding?

A

It promotes heterozygosity and therefore vigour.

49
Q

What is Hybrid Vigour (heterosis)?

A

The phenomenon where the F1 hybrid is more vigorous than both its parents.

50
Q

What happens to vigour as heterozygosity is reduced?

A

Vigour is also reduced.

51
Q

What might cause heterosis?

A

A - Dominance Hypothesis: Deleterious recessive mutations of parents are masked by each other’s dominant alleles, so F1 has all the “good” alleles.
B - Over-Dominance Hypothesis: having alleles for proteins with different activities gives a broader range of function.

52
Q

How can homozygous parents be selected for the

phenotypes of their F1 progeny?

A

Artificial Cross-Pollenation - Preventing the plants from self-pollinating by removing male or female features.
> Tassles removed in maize.
> Mutant rice mitochondria that prevent pollen development.

53
Q

How can heterosis be maintainted?

A

Vegitative propagation (asexual seed production).

54
Q

How does polyploidy occur?

A

Chromosomes are not pulled apart properly (non-disjunction) so the cell inherits twice the normal amount of chromosomes.

55
Q

How can polyploidy be induced?

A

Adding Colchicene, (from autum crocus) causes depolymerisation of spindles.

56
Q

How can haploid//monoploid plants be obtained?

A

Via pollen culturing.

57
Q

What use does a haploid//monoploid plant have?

A

Since no alleles are masked, they can be used to select lines that do not carry undesirable, recessive mutations.

58
Q

What are the consequences of polyploidy?

A
  1. Bigger cells (more DNA = Bigger nucleus).
  2. Sterility (if ODD) or reduced fertility (if EVEN).
  3. Prolonged heterosis (altered segregation).
59
Q

What is autopolyploidy?

A

Increase in the SAME set of chromosomes.

60
Q

What is allopolyploidy?

A

Increases with DIFFERENT sets of chromosomes.

61
Q

What effect does allopolyploidy have on inter-species hybrids?

A

They restore fertility - Normally, maternal and paternal chromosomes do not assocaite at the start of meiosis, but if there is a double chromosome number, each chromosome can pair with its homologue.

62
Q

Give examples of polyploid plants.

A

> Bread wheat is an allohexaploid (complicated origin).
Triticale, made by Colchicine doubling following the hybrid.
Karpechenko’s “Raphanobrassica” made by spontaneous doubling following the hybrid.

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