Basic Agricultural Genetics – Agricultural Sciences Grade 12 Questions and Answers

Basic Agricultural Genetics – Agricultural Sciences Grade 12 Questions and Answers

QUESTIONS

• Answer the questions below. Check your answers afterwards and do corrections.
• Give yourself one hour.
• Marks: 100

1. Study the diagram. Then choose the best answer for each question. Write down only the question number and the letter that represents the best answer.
   

   	Paternal
   Maternal		B	b
   	B	BB	Bb
   	b	Bb	bb

1.1 This diagram is called a _________.

1. Monohybrid cross
2. Mendelian inheritance
3. Punnett square
4. dihybrid cross (1)

1.2 The capital B in the diagram indicates a _________.

1. genotype
2. dominant allele
3. phenotype
4. gamete (1)

1.3 In the diagram, both the maternal and the paternal organism have:

1. the phenotype Bb
2. the phenotype BB
3. the genotype Bb
4. the allele Bb (1)

1.4 In the diagram, assuming the maternal organism is a dog with a black coat (B) and the paternal organism is a dog with a white coat (b), _________ of the offspring will be black while _________ will be white.

1. 25% ; 75%
2. 50% ; 50%
3. 75% ; 25%
4. None of the above. (2)

2. Fill in the missing words.
   2.1 Chromosomes divide during ________ into a pair of ________. (2)
   2.2 An homologous chromosome pair ________ during ________ resulting in a ________ cell. (3 × 1 = 3)
3. Cow parsley (Anthriscus sylvestris) produces a purple-leafed variant called
   Ravenswing. The purple colour is produced by the allele R which shows incomplete dominance over the allele for green leaves (r). Heterozygotes (Rr) produce green and purple spotted leaves.
   3.1 Show the genotypes that result from a cross between the Ravenswing variant and a green plant. (2)
   3.2 What are the resulting phenotypes? (2)
   3.3 Show what genotypes and phenotypes result from crossing the progeny of the cross mentioned in (3.1), namely F1 × F1. (3)
4. Tortoise shell cats (red and black colour combination) are always female because the alleles for the red and black colouring are linked to the X chromosome. This means that tom cats can only be red (O) or black (o).
   Use a Punnett square to determine how many tortoise shell cats will be produced by crossing red, black and tortoise shell females with red or black males. (Hint: You only need to show the female progeny.) (6)
5. Sex is a qualitative characteristic in humans and most animals.
   5.1 Which sex has homologous chromosomes?
   5.2 Name a sex-linked characteristic found in animals.
   5.3 What is the sex ratio of offspring after sexual reproduction? (3 × 1 = 3)
6. Some genetic characteristics are quantitative.
   6.1 Name an example of a quantitative genetic characteristic. (1)
   6.2 Quantitative genes have ________ effects. (1)
   6.3 What quantitative characteristics would be important in agricultural production? (2)
7. Explain briefly how external factors can cause variation in individuals. (2)
8. Polyploidy in plants is a chromosomal abnormality which results from ________ of chromosomes during replication. (1)
9. Spontaneous mutations arise in the DNA of all living organisms.
   9.1 Give four examples of spontaneous DNA mutations. (4)
   9.2 Explain how mutations can affect gene function. (5)
   9.3 What effects can mutations have on organisms? (3)
10. Explain the difference between inherited and non-inherited mutations. (2)
11. Explain why sexual reproduction is a cause of genetic variation. (4)
12. Name five mutagens that can be used to cause DNA mutations. (5)
13. Selection of the animals that have adapted the best to their environment is called ________. (2)
14. What adaptive characteristics could you expect to find in desert plants? (5)
15. Artificial selection is the process used by humans to improve plants and animals.
    15.1 What type of characteristics should be selected for breeding plants and animals? (3)
    15.2 What problems could be encountered when performing selective breeding? (2)
    15.3 Explain the principle of hybridization and its application in agronomy. (5)
    15.4 What are the two main disadvantages of pure bred species? (2)
    15.5 Why do most species crosses in animals result in infertility? (1)
    15.6 Why are species crosses possible in plants? (1)
16. What is the advantage of genetic engineering or transgenics over selective breeding? (2)
17. Name four aims of genetic engineering in crops. (4)
18. GMOs are used widely in agriculture.
    18.1 Identify the main environmental concerns about GMOs. (3)
    18.2 How can you identify an escaped GMO? (1)
    18.3 Name the bacterium used to transfer genes into GMOs. (1)
    18.4 Explain why the bacterium named in (18.3) is used. (4)
19. Various types of breeding systems are used in agriculture.
    19.1 Name one example of the result of a species crossing.
    19.2 Give an example of cross-bred cattle.
    19.3 Give an example of pure-bred cattle.
    19.4 What type of plant breeding system can be used to develop a new plant cultivar? (4 × 1 = 4)
20. Name the selection system used for sires in animal science. (1)
21. What value is used to rate sires with good production characteristics? (1)
22. Mention the role biometrics plays in performance testing. (1)

ANSWERS

1. Study the diagram.
   1.1 C Punnet square
   A dihybrid cross (1)
   1.2 B dominant allele (1)
   1.3 C genotype Bb (1)
   1.4 C 75% ; 25% (2)
2. Fill in the missing words.
   2.1 mitosis; chromatids. (2)
   2.2 separates; meiosis; haploidl. (3 × 1 = 3)
3. Cow parsley produces a purple-leafed variant called Ravenswing:
   3.1 RR × rr = all 4 are Rr. (2)
   3.2 All purple and green spotted (2)
   3.3 RR (purple), 2 Rr (spotted), rr (green). (3)
4. Tortoise shell cats Punnet square: (6)
   
5. Sex is a qualitative characteristic in humans and most animals:
   5.1 Female
   5.2 Tortoise shell colouring in cats.
   5.3 50:50 (3 × 1 = 3)
6. Quantitative genetic characteristics:
   6.1 Milk production/ tallness, etc. (any acceptable answer. (1)
   6.2 cumulative (1)
   6.3 Milk or other production attributes. (2)
7. Non-genetic factors such as nutrition, climate and disease can cause variation in genetically similar animals. (2)
8. replication (1)
9. Spontaneous mutations arise in the DNA of all living organisms.
   9.1 Point mutations such as apurination, due to base substitution; sequence mutation such as indels; chromosome translocations, substitutions or replicationss. (4)
   9.2 Mutations cause a change in the protein for which the gene encodes; this change in the protein causes either the loss of a function or gain of function.
   The effect will depend on the importance of the function affected. (5)
   9.3 Harmful, beneficial or neutral. (3)
10. Mutations in somatic cells (e.g. cancer) are not inherited while those occurring in the gametes are inherited. (2)
11. Sexual reproduction brings about recombination of new alleles which gives rise to offspring that vary from their parents; asexual reproduction as in cloning produces the exact replica of the parent, with no genetic variation. (4)
12. X-rays, UV radiation, alkylating agents, intercalating agents, and base analogues. (5)
13. Natural selection. (2)
14. succulent leaves, waxy leaves, thorny leaves and long roots to search for water. (5)
15. Artificial selection:
    15.1 Must be heritable, measurable and economically important. (3)
    15.2 Can select unwanted characteristics such as disease susceptibility. (2)
    15.3 Hybridisation is the crossing of two purebred individuals to produce a new variant; in agronomy it is used to produce vigorous F1 offspring (hybrid vigour). (5)
    15.4 Harmful genes are selected, gradual decline in vigour. (2)
    15.5 Different chromosome numbers make fertilisation impossible. (1)
    15.6 Polyploidy or chromosome replication occurs often in plants and can make the chromosome number compatible (1)
16. Transgenics provides genes which are not otherwise available to the species. (2)
17. Increased production, disease resistance, drought resistance, herbicide resistance. (4)
18. GMOs are used widely in agriculture.
    18.1 Escape of genes which are used to produce toxic substances ( for example pharmacological substances) (3)
    18.2 Laboratory analysis for a genetic marker or detecting the inserted gene. (1)
    18.3 Agrobacterium (1)
    18.4 It inserts itself into the DNA of the host plant so carries the new genes into the genome of the plant. (4)
19. Breeding systems used in agriculture:
    19.1 Mule, or any other acceptable answer.
    19.2 Bonsmara, or any other acceptable answer.
    19.3 Friesland, or any other acceptable answer.
    19.4 Pedigree breeding (4 × 1 = 4)
20. Progeny testing (1)
21. Breeding value (1)
22. It is used to evaluate the measurable traits which are being selected (improvement or not). (1)