Year 10 Science · Unit 1 · Lesson 6
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Learning Goals
Order the steps
Number the events from 1 to 8 to show the correct order of a selective breeding programme to develop disease-resistant wheat. Event 1 = what happens first.
| Order | Step in the breeding programme |
|---|---|
| Select the parent plants that showed the highest disease resistance from the test crops | |
| Cross-breed (pollinate) the selected resistant plants with each other across many generations | |
| Identify the desired trait, in this case, resistance to wheat rust fungus | |
| Release the new disease-resistant variety to Australian farmers after several years of testing | |
| Grow test crops from seeds of different wheat varieties and expose them to the wheat rust fungus | |
| Collect a diverse starting population of wheat varieties from different regions | |
| Evaluate the offspring for disease resistance in controlled field trials | |
| Stabilise the new variety by breeding resistant offspring together until the trait breeds true |
Real-world context
The Cavendish banana, the variety sold in virtually every Australian supermarket, is produced through clonal propagation: every plant is genetically identical, propagated from cuttings rather than seeds. In the 1990s, the Gros Michel banana, which dominated before the Cavendish, was wiped out globally by Panama disease (Fusarium wilt). Today the Cavendish faces a new strain of Panama disease, Tropical Race 4, which has already reached parts of Queensland and is spreading.
(a) Explain why the genetic uniformity of Cavendish bananas makes them particularly vulnerable to Panama disease Tropical Race 4. Use the concepts of genetic diversity and selective pressure in your answer.
(b) Suggest one long-term strategy that banana farmers or scientists could use to protect the industry from future disease outbreaks. How would this strategy address the genetic uniformity problem?
1. Australian Merino sheep were selectively bred over centuries for their fine wool. Describe two specific traits a breeder would select for, and explain why selective breeding only works on heritable (genetic) traits, not traits caused entirely by the environment.
2. Inbreeding depression occurs when closely related individuals are repeatedly bred together, causing reduced fitness in offspring. Explain the genetic reason why inbreeding depression occurs, using the terms homozygous and recessive alleles.
Wrap Up
In one sentence, what was the main idea of this lesson?