PMS L1

Question 1

What are Geographical Centers of Crop Diversity and who came up with the theory?

Answer 1

• Nicolai Vavilov, Russian biologist, popularised the concept.

-These centres correspond to areas of botanical diversity and coincide with the early human societies and plant domestication.

Question 2

Describe Human Migration and the first Domestication of Crops

Answer 2

• AMHs originated in East Africa and migrated into Europe, Asia, and the Americas over 65,000 years ago.
• 15,000 years ago, they had reached Mesoamerica and transitioned from a
  nomadic lifestyle to agriculture, beginning the domestication of local plants such as maize.

Question 3

Describe the Archaeological Evidence for Maize Domestication:

Answer 3

• Evidence from the Tehuacan Valley, Mexico, indicates maize was domesticated 7,000 years ago
• Plant remains show a progression from
  small, vestigial forms to modern ones due to selective breeding.

Question 4

What is the progenitor of Maize?
Give 3 differences between Teosinte and modern Maize.

Answer 4

• Teosinte, a Mesoamerican subspecies of Zea mays.
• Maize has larger cobs and kernel architecture
• Maize has apically dominant growth (less branched)
• Maize lacks protective seed coverings (unlike Teosinte)

Question 5

Outline the breeding habits of early Maize and Teosinte. Define the terms used.

Give an example seed bank that preserves the rich diversity of maize.

Answer 5

• Self-fertilising and true-breeding plants with natural genetic variation.
• True breeding: parents with a particular phenotype produce offspring only with the same phenotype
• International Maize and Wheat
  Improvement Center (CIMMYT).

Question 6

Describe the spread of Maize

Answer 6

• Maize became a staple crop across Mesoamerica, taking on cultural and religious significance.
• It spread across North and South America.

Question 7

Describe the results of genetic studies studying differences between Maize and Teosinte, giving examples.

Give a relevant citation.

Answer 7

• 90% of differences due to a handful of genetic loci - e.g. tb1 is elevated in Maize, repressing side branching.
• Branching, morphology, and floral
  structure affected.
• J Doebley, A Stec, 1991.

Question 8

Outline the history of Maize production in the US

Answer 8

• Europeans adopted maize. By the 1800s it was widely planted in the Midwest.
• Farmers were self-sufficient, using traditional methods and minimal external inputs.
• In the 1900s, scientists (G.H. Shull) observed hybridisation increased yields. Commercialisation of hybrid seed by entrepreneurs like Roswell Garst and Henry Wallace.
• Farming transformed to an industrialised
  agribusiness, reducing maize diversity and increasing reliance on synthetic inputs.

Question 9

What was the Green Revolution?

Answer 9

• From the 1960s, dramatic increase in worldwide yield through selective breeding. Efforts led by Norman Borlaug.
• Most increases in developed world, less so in Africa.

Question 10

When was GM developed?
Through what method?

Answer 10

• Started in 1983, enabling precise genetic modications.
• Agrobacterium tumefaciens used, a bacterial pathogen.

Question 11

Outline how Agrobacterium transfers DNA and for what purpose.

Answer 11

• A. tumefaciens binds to plant cells, transferring a segment of DNA (T-DNA) from a Ti Plasmid via its Type IV secretion system.
• T-DNA causes tumour formation and opine production in the plant - food.

Question 12

How can Agrobacterium be modified for GM uses? Sketch this system.

Answer 12

• Ti Plasmid disassembled (due to its modular nature) and tumourigenesis and opine production functions removed.
• DNA transfer function maintained on a large, disarmed helper plasmid.
• Smaller plasmid contains customised T-DNA segment + replication machinery + bacterial selection marker. Both plasmids form a binary plasmid system
• Advantage that only the smaller plasmid is replicated, more efficient.

Question 13

Outline a different method of genetic transfer

Answer 13

• Biolistic method (high-velocity DNA-coated particles) used for transforming
  plants and organelles. (Method of choice for organelles)
• Allows targeted delivery and expression of genes, demonstrated through techniques like fluorescent protein tagging.

Question 14

What are the applications of transgenic technology?

Answer 14

• Exploration of gene structure
• Crop improvement
• Use of reporter genes to study genotype-phenotype links.