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SS3: AGRICULTURAL SCIENCE - 1ST TERM

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  1. Crop Improvement | Week 1
    9 Topics
    |
    1 Quiz
  2. Animal Improvement | Week 2
    6 Topics
    |
    1 Quiz
  3. Animal Health Management I - Introduction | Week 3
    7 Topics
    |
    1 Quiz
  4. Animal Health Management II | Week 4
    5 Topics
    |
    1 Quiz
  5. Animal Health Management III | Week 5
    7 Topics
    |
    1 Quiz
  6. Aquaculture | Week 6
    11 Topics
    |
    1 Quiz
  7. Apiculture or Bee-keeping | Week 7
    10 Topics
    |
    1 Quiz

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  • Theory Questions & Answers
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Evaluation Questions – Crop Improvement:

(a) Define crop improvement.

(b) Copy and complete the table below based on Mendel’s Law of Independent Assortment of Genes (Dihybrid inheritance).

 TCTctCtc
TCTTCC   
Tc TTcc  
tC   ttCc
tc  ttcC 

Use the following information: T = Tall; C = Coloured; t = Dwarf; c = White. (Where T and C are dominant characters; while t and c are recessive characters)

(c) Calculate the percentage of plants in (b) above that are:
(i) Tall coloured;
(ii) Tall white;
(iii) Dwarf coloured;
(iv) Dwarf white

(d) Define the term hybridization

(e) State five aims of crop improvement.

(f) Describe a monohybrid cross as explained by Mendel’s Law of segregation. Illustrate your answers with clearly labelled diagrams.

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Evaluation – Crop Improvement

(a) Define crop improvement.

Answer:

Crop improvement is defined as the breeding and development of plant varieties which are better than the local existing varieties.

It is the science that deals with the development of new crop varieties with superior quality and quantity.

 

(b) Copy and complete the table below based on Mendel’s Law of Independent Assortment of Genes (Dihybrid inheritance).

TC Tc tC tc
TC TTCC
Tc TTcc
tC ttCc
tc ttcC

Use the following information: T = Tall; C = Coloured; t = Dwarf; c = White. (Where T and C are dominant characters; while t and c are recessive characters)

Solution

TC Tc tC tc
TC TTCC TTCc TtCC TtCc
Tc TTCc Ttcc TtCc Ttcc
tC TtCC TtCc ttCC ttCc
tc TtCc Ttcc ttcC ttcc

 

(c) Calculate the percentage of plants in (b) above that are:
(i) Tall-coloured;
(ii) Tall white;
(iii) Dwarf coloured;
(iv) Dwarf white.

Solution:

Tall coloured: TTCC, TTCc, TtCC, TtCc, TTCc, TtCc, TtCC, TtCc & TtCc = 9
Tall white: TTcc, Ttcc, Ttcc, = 3
Dwarf Coloured: ttCC, ttCc, ttCc = 3
Dwarf white: ttcc = 1

Total number of plants = 9 + 3 + 3 + 1 = 16

Calculation of percentage of plants:

Tall coloured = \(\frac{9}{16} \scriptsize \: \times \: 100 = 56.25 \% \)

Tall white = \(\frac{3}{16} \scriptsize \: \times \: 100 = 18.75 \% \)

Dwarf Coloured = \(\frac{3}{16} \scriptsize \: \times \: 100 = 18.75 \% \)

Dwarf white = \(\frac{3}{16} \scriptsize \: \times \: 100 = 6.25 \% \)

 

(d) Define the term hybridization.

Answer: Hybridization is a method by which an offspring is produced through the crossing of two different plant varieties of the same species. It can also be defined as the development of plants by combining the heritable qualities of one plant with that of another through the fertilization of female with male gametes.

 

(e) State five aims of crop improvement.

Answer:

Aims of Crop improvement include:

(i) to increase yield.
(ii) to improve the quality of produce.
(iii) to meet the needs of growers.
(iv) to adapt to wide climatic conditions.
(v) to increase resistance to diseases.
(vi) to improve harvesting qualities.
(vii) to obtain uniformity of plant.
(viii) to improve the nutritional value of the produce.
(ix) to meet the needs of processors/industrialists.

 

(f) Describe a monohybrid cross as explained by Mendel’s Law of segregation. Illustrate your answers with clearly labelled diagrams.

Answer:

The law of segregation can be demonstrated in a monohybrid cross, where a cross is made between purebred homozygous plants, e.g. one with dominant purple flowers (BB) and one with recessive white flowers (bb).

  • The genotype of all the F1 generation plants is Bb.
  • From the figure, all the offspring in the F1 generation all have purple flowers (the dominant trait is B – purple, Hence, the phenotype is plants with all purple flowers but they are heterozygous, i.e. not pure breeds.)

The heterozygous F1 generation plants are then self-pollinated to obtain the second filial generation (F2) as shown below.

  • The genotype of the F2 plants are:
    • 1 BB
    • 2 Bb
    • 1 bb
  • The genotypic ratio is 1:2:1
  • The phenotypes are:
    • 3 plants with purple flowers
    • 1 plant with a white flower
  • The phenotypic ratio is 3:1

Segregation occurs in the F2 generation.

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