Biology • Year 12 • Module 6 • Lesson 14
Reproductive Technologies — Artificial Insemination & Artificial Pollination
Apply the lesson to Australian agricultural data: artificial insemination in dairy herds, and hand-pollination case studies in commercial orchards.
1. Australian dairy AI yield data
An Australian dairy cooperative compared average annual milk yield per cow in two breeding programs over five lactation years. Program X uses natural service from on-farm bulls only. Program Y uses artificial insemination with semen from top-ranked Holstein bulls listed on the national Australian Breeding Values index. Other management (feed, housing, veterinary care) is matched between programs. 8 marks
| Lactation year | Program X — natural service (L/cow/year) | Program Y — AI program (L/cow/year) | Note |
|---|---|---|---|
| 1 (baseline) | 6 200 | 6 250 | Same starting genetics |
| 2 | 6 240 | 6 520 | First AI-sired daughters in herd |
| 3 | 6 290 | 6 880 | Second AI generation |
| 4 | 6 320 | 7 240 | Third AI generation |
| 5 | 6 350 | 7 510 | Bull mix unchanged |
Stylised data based on patterns from Dairy Australia herd-improvement reports. Average yields are approximate; trends reflect typical AI gains in Holstein-Friesian herds.
1.1 Describe the trend in average milk yield per cow for Program X and Program Y across Years 1–5. 2 marks
1.2 Calculate the percentage increase in average milk yield per cow between Year 1 and Year 5 for each program. Show your working. 2 marks
1.3 Using lesson content, explain why Program Y's yield rose faster than Program X's. Refer to controlled breeding, selected male and trait control. 3 marks
1.4 A farmer reads the data and concludes: "AI guarantees every calf will produce more milk than her dam." Briefly explain why that conclusion is too strong. 1 mark
2. Hand-pollination in Australian orchards
Three orchards trialled hand-pollination (a form of artificial pollination) on a single block, comparing it to an adjacent block left to open (bee + wind) pollination during the same flowering season. The graph below shows the resulting average fruit yield in tonnes per hectare. 8 marks
Stylised yield data after Goodwin (HIA pollination reports) and orchard-extension case studies in Tasmania, the NSW Riverina and Victoria's Goulburn Valley.
2.1 In which orchard is the absolute yield difference between hand and open pollination largest? Quote the figures. 2 marks
2.2 In which orchard is the percentage uplift from hand pollination largest? Show working. 2 marks
2.3 Kiwifruit are dioecious — male and female flowers occur on separate vines and are not particularly attractive to bees. Use this fact, plus the lesson's definition of artificial pollination, to explain why the Riverina kiwifruit orchard shows the largest percentage uplift. 3 marks
2.4 A grower argues: "Hand pollination is just cloning by another name — the new fruit must be genetically identical to the donor flower." Briefly explain why this claim is biologically wrong. 1 mark
3. Apply to a scenario — a Merino stud chooses AI
A NSW Merino stud wants to lift the average clean fleece weight of its ewe flock. Two strategies are debated:
- Strategy A. Continue natural service using the stud's own 12 rams.
- Strategy B. Use AI with frozen semen from three Australian Merino industry "elite" rams ranked highly for fleece weight on the MERINOSELECT index.
7 marks
3.1 Explain one reason Strategy B would lift fleece weight in the next lamb crop more reliably than Strategy A. Use the lesson terms selected male and controlled breeding. 2 marks
3.2 Identify one reason the AI program will not guarantee that every lamb has heavier fleece than its dam. Use the lesson's "outcome limit" wording from Card 4. 2 marks
3.3 A buyer claims: "Because the elite rams are used widely across Australia, AI changes the underlying DNA sequence of every Merino in the country." Evaluate this statement. 3 marks
Q1.1 — Trend description (2 marks)
Both programs start at almost identical baseline yields (≈6 200–6 250 L). Program X rises only slightly across Years 1–5 (6 200 → 6 350 L), an essentially flat increase. Program Y rises steadily and substantially (6 250 → 7 510 L) with the gap widening each year.
Marking: 1 mark — describes X as broadly flat with small increase. 1 mark — describes Y as a steady, larger rise with the AI-vs-natural gap widening over time.
Q1.2 — Percentage uplift (2 marks)
Program X: (6 350 − 6 200) ÷ 6 200 × 100 ≈ 2.4%. Program Y: (7 510 − 6 250) ÷ 6 250 × 100 ≈ 20.2%.
Marking: 1 mark each for the correct calculation (accept ±0.2%). Working must be shown.
Q1.3 — Why Program Y rose faster (3 marks)
AI lets the herd's cows be inseminated with semen from a small group of selected males (elite Holstein bulls with high Australian Breeding Values for milk yield) rather than with sperm from the stud's average on-farm bulls [1]. This is controlled breeding: the breeder, not chance mating, decides which sperm fertilises each ovum [1]. Because the chosen bulls carry alleles associated with high milk production, the probability that their daughters inherit yield-related allele combinations is greater, so average daughter yield rises generation after generation — trait control in action [1].
Marking: 1 mark each for selected male, controlled breeding, trait control explicitly linked to the yield trend.
Q1.4 — Why "guarantees" is too strong (1 mark)
AI improves the probability of inheriting yield alleles but does not guarantee a phenotype: meiosis in the bull still reshuffles alleles, the dam contributes a different gamete each time, and milk yield is influenced by many genes and environmental factors. [1]
Q2.1 — Largest absolute difference (2 marks)
Tasmanian apple: hand 38 − open 28 = 10 t/ha difference [1] — the largest absolute gap of the three orchards [1].
Q2.2 — Largest percentage uplift (2 marks)
Riverina kiwifruit: (32 − 18) ÷ 18 × 100 ≈ 78% [1]. Apple ≈ (38−28)/28 ≈ 36%; pear ≈ (30−22)/22 ≈ 36%. Kiwifruit clearly has the largest percentage uplift [1].
Q2.3 — Why kiwifruit benefits most (3 marks)
Kiwifruit are dioecious, so open pollination relies on insect or wind transfer of pollen from separate male vines onto female-flower stigmas, and bees do not find kiwifruit especially attractive [1]. Open pollination therefore often delivers insufficient pollen to female stigmas, capping fruit yield. Artificial (hand) pollination — controlled transfer of selected pollen onto each recipient stigma — bypasses that bottleneck and guarantees ample pollen on every flower [1]. For apple and pear (which are insect-pollinated and at least partially self-fertile), open pollination is already reasonably efficient, so the relative uplift from controlling pollen delivery is smaller [1].
Q2.4 — Hand pollination is not cloning (1 mark)
Hand pollination still produces seeds by ordinary fertilisation — pollen carries male gametes that fuse with female gametes inside the ovule. Offspring are sexually produced and carry a combination of alleles from both donor and recipient, not a clone of either. The technology only controls which pollen reaches the stigma; it does not bypass meiosis or fertilisation. [1]
Q3.1 — Why Strategy B works (2 marks)
The breeder can choose selected males with high MERINOSELECT breeding values for clean fleece weight, instead of using the average on-farm rams [1]. AI lets one elite ram's semen fertilise hundreds of ewes — controlled breeding across the whole flock — so the probability that lambs inherit alleles associated with heavier fleece rises in a single generation [1].
Q3.2 — Why no guarantee per lamb (2 marks)
AI controls only which sperm fertilises which egg; it does not eliminate biological variation [1]. Meiosis in the ram and ovulation in the ewe still produce gametes carrying different allele combinations, and fleece weight is polygenic and environment-influenced, so any individual lamb may have lighter fleece than her dam (Card 4 "outcome limit") [1].
Q3.3 — Evaluate the DNA-sequence claim (3 marks)
The claim is biologically wrong [1]. AI does not edit DNA sequence — it only controls which sperm enters which female reproductive tract; the alleles carried by sperm and egg are unchanged, and meiosis still operates normally (Card 1 Exam Trap) [1]. What AI does change is the frequency of certain alleles in the population, because widely used elite rams contribute disproportionately to the next generation; but each animal's DNA sequence still comes from ordinary inheritance of alleles that already existed in the gene pool [1].