2
Science of Plants in Agriculture
Pl.Sci 102
Test # 3
November 9th, 2005
10:30 – 11:20
Name:
Answer all 19 questions
A bonus question is available for an extra 3 points
A total of 100 points (plus 3 bonus points) are available
Points available from each part of each question
are shown in bold square parenthesis
Try to be as brief and concise as possible
Please write in a legible form
Make sure that any additional paper used
is attached to the questionnaire
Genes, Mendel and Meiosis
1. Fill in the three blanks to complete the central dogma of genetics. [6 points]
RNA
Nucleic Amino
acid acid
2. Briefly, describe the difference between homozygous and heterozygous alleles. [5 points]
3. What is the difference between a recessive allele and a dominant allele? [5 points]
Plant Breeding
4. List two features that differentiate self-pollinating plant species from out-pollinating species. [4 points]
1.
2.
5. Fill in the blanks in the table below with either the most suitable cultivar type, a description of the cultivar type shown, or one (or more) crop(s) that are developed from the specified cultivar type. [8 points]
Cultivar type / Characteristics / CropsSelf-pollinating mating system, annual seed production, able to develop homozygous lines. / wheat, barley, pea, canola
Out-pollinating / Out-pollinating species, annual, biennial or perennial, highly heterozygous and heterogeneous.
Out-pollinating, annual or biennial, must show high heterosis, usually must have system of hybrid seed production. / corn, tomato, onion, sunflower
Clone / potato, apple, bulbs, strawberry
6. A plant breeder makes a cross between a disease resistant wheat cultivar (RR) and a disease susceptible wheat cultivar (rr). The disease resistance gene (R) is completely dominant over the recessive susceptible gene (r). The first generation (F1) is self pollinated and 1,600 second generation (F2) plants were grown out in the field. At harvest all the disease susceptible plants are discarded and a single seed from each of the resistance ‘selected’ plants were grown out in the F3 generation. How many of the F3 plants would you expect be disease resistant in this generation? [6 points]
7. The first stage of a breeding scheme is to create (or find) genetic variability. List two methods used by plant breeders to create genetic variability. [4 points]
1.
2.
8. Most plant breeders aim to increase grower profitability. Outline two characteristics of new cultivars that would increase grower profitability. [4 points]
1.
2.
Plant diseases and insects
9. Fill in the blanks in the table below with the most appropriate type of disease, a suitable disease description, or an example of one (or more) disease in the appropriate disease type. [10 points]
Pest type / Description / ExampleInsects / Many insects have a wide host range but some are species specific. Infestations tend to be seasonal. Can spread rapidly (winged) or slowly (non-flyers).
Single stranded RNA (in plants). Unable to multiply outside host (obligate). Many pathotype differentiated. Spread rate is related to vector. / Barley yellow dwarf virus, potato LR virus
Bacteria / Potato ring-rot, vascular wilts.
Spore forming, microscopic to large soil-borne organisms that have log persistence in soils. Spread slowly and usually man-assisted. / Potato wart, Cereal take-all.
Air-borne fungi / Spore forming, microscopic air-borne organisms that are usually pathotype differentiated. Spread rapidly.
10. List two adverse effects that plant pests have on our crops? [4 points]
1.
2.
11. Given that plants are resistant to a pathotype differentiated disease because they have at least one copy of dominant resistance gene (locks), which can only be overcome, and hence the plant become susceptible to the disease, if the disease pathotype has two copies of the appropriate recessive virulence gene (keys). Given that plant resistance genes are denoted as capital letters (A, and B) with susceptible genes as lower case letters (a, or b), and that disease virulent genes are denoted as a’, or b’ with disease avirulant genes donated as A’, or B’, would the following plants be resistant or susceptible to the associated disease pathotype? [6 points]
Plant phenotype / Disease genotype / Plant responseNo resistance genes / No virulence genes
A_ bb / A’a’ b’b’
A_ B_ / a’a’ b’b’
12. Outline the two major features of vertical and horizontal disease resistance. [4 points]
Vertical resistance:
Horizontal resistance:
Weed control
13. Fill in the blanks in the table below with the most appropriate mode of action, and the effects of each herbicide class on plant for the following groups of herbicide [6 points].
Group / Description1 / inhibitors, binds to and disrupts fatty acid synthesis, which leads to degeneration.
2 / inhibitors, binds to and disrupts synthesis of branched .
9 / inhibitor, binds to synthase and disrupts pathway, which is responsible for producing the precursors of aromatic amino acids. Commonly called .
14. Crops infested with weedy species can exhibit reduced yield. What three things do weeds compete with crop plants for that causes crop yield reduction? [6 points]
1.
2.
3.
15. List four methods used to control weeds in crop plants. [4 points]
1.
2.
3.
4.
Biotechnology – molecular markers and plant transformation
16. What is a restriction enzyme? [4 points]
17. What can be achieved by plant transformation techniques that are not possible with traditional plant breeding methods? [4 points]
18. How does Agrobacterium tumefacians cause crown galls in plants? [4 points]
19. Describe (briefly) three of the processes necessary to successfully complete plant transformation. [6 points]
1.
2.
3.
Bonus Questions
[3 points]
Who were the three scientists who re-discovered Mendel’s theory of genetic inheritance.
1.
2.
3.