--- title: "Why don't brothers and sisters look the same?" subtitle: "Year 9 Biology · Reproduction · Lesson 7" --- # Why don't brothers and sisters look the same? **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** Two kittens from the same litter can be black and ginger. A strawberry plant's runners grow into plants identical to it. Same question, two answers. :::teacher-note **In one sentence:** Students compare sexual and asexual reproduction and explain why sexual reproduction produces varied offspring (AC9S9U02, node 3, a hinge node). **Students should be able to say:** I can explain why offspring of sexual reproduction vary. I can explain why asexual reproduction makes clones. I can give an advantage of each. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Engage :::keep-together **Two parents have several offspring. What do you predict?** ☐ Each one is an exact half-way blend of the parents ☐ All the offspring look the same, because they have the same parents ☐ They all look like one parent ☐ Each offspring is a different mix of the parents' features My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** Each offspring is a different mix. Each gets a random one of each parent's two copies of every gene, so brothers and sisters differ (unless they're identical twins). ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: two ways to reproduce :::keep-together ### Which kind **Sexual or asexual reproduction?** Groups: Sexual, Asexual - Two parents: {{field-15}} - Offspring are clones of the parent: {{field-15}} - Gametes fuse at fertilisation: {{field-15}} - No partner needed: {{field-15}} - Offspring vary: {{field-15}} - A strawberry plant's runners: {{field-15}} ::: :::teacher-note **Answer:** Two parents → Sexual; Offspring are clones of the parent → Asexual; Gametes fuse at fertilisation → Sexual; No partner needed → Asexual; Offspring vary → Sexual; A strawberry plant's runners → Asexual ::: :::keep-together ### Why they vary **Why are the offspring from sexual reproduction different from each other?** ☐ Each gets a random one of each parent's two copies of every gene, so each gets a different combination ☐ The environment changes their genes ☐ One parent's genes are stronger ☐ Some offspring get more genes ::: :::teacher-note **Answer:** Each gets a random one of each parent's two copies of every gene, so each gets a different combination ::: :::keep-together ### Survival **A new disease kills plants with one particular set of genes. Which population is more likely to survive?** ☐ A population from sexual reproduction: some individuals are likely to have genes that resist it ☐ Both the same ☐ A population of clones: they are all strong ::: :::teacher-note **Answer:** A population from sexual reproduction: some individuals are likely to have genes that resist it ::: :::keep-together ### Many or few **A cod releases millions of eggs into the sea and leaves them. A kangaroo raises one joey at a time in her pouch for months. Why do both strategies work?** ☐ The kangaroo has one joey because there isn't enough food in Australia ☐ A parent has limited energy: the cod spreads it over millions of eggs that mostly die, the kangaroo puts it into one joey likely to survive ☐ More offspring is always better, so the cod's way is best ☐ The cod's eggs are clones, so they don't need care ::: :::teacher-note **Answer:** A parent has limited energy: the cod spreads it over millions of eggs that mostly die, the kangaroo puts it into one joey likely to survive ::: :::typical ## Elaborate: which suits? :::keep-together **Aphids reproduce asexually all summer, then sexually in autumn before winter. Why might that be useful?** ☐ It makes no difference ☐ Cloning only works in warm weather ☐ Fast cloning while conditions are good; variation before the harsh, changing winter ☐ They run out of partners in summer ::: :::teacher-note **Answer:** Fast cloning while conditions are good; variation before the harsh, changing winter ::: ::: :::wider ## Elaborate: bananas :::keep-together **Nearly all supermarket bananas (Cavendish) are clones grown from cuttings. Panama disease is spreading through banana farms. Why are growers worried?** ☐ Clones grow too slowly ☐ Disease only affects clones ☐ The clones all have the same genes, so if one is vulnerable, every plant is ☐ Clones can't make bananas ::: :::teacher-note **Answer:** The clones all have the same genes, so if one is vulnerable, every plant is This happened before: the Gros Michel banana was wiped out of commercial farming in the 1950s by an earlier strain of Panama disease. ::: ::: :::typical ## Elaborate: who decides what gets researched? :::keep-together ### The need **Why did a Cavendish banana that resists Tropical Race 4 become a research focus in Australia?** ☐ Society needed it: a fruit most Australians eat, and many growers' farms and jobs, were at risk from a disease with no cure ☐ Scientists research only what interests them, whatever anyone needs ☐ It was the quickest, easiest banana research to do ☐ A law says every crop must be gene-modified ::: :::teacher-note **Answer:** Society needed it: a fruit most Australians eat, and many growers' farms and jobs, were at risk from a disease with no cure Research costs money and time. Needs that matter to many people, such as food and jobs, attract the funding and the effort. ::: :::keep-together ### Values **Some people don't want to eat gene-modified food. How can a value like that influence the research?** ☐ It can steer researchers towards other methods as well, such as breeding resistant bananas, and affect whether a GM banana is ever grown ☐ It changes how fast the fungus spreads ☐ It can't: people's values never affect research ☐ It makes the resistant banana unsafe to eat ::: :::teacher-note **Answer:** It can steer researchers towards other methods as well, such as breeding resistant bananas, and affect whether a GM banana is ever grown Society's values shape which questions get asked, which methods are used and whether a result is taken up. ::: ::: ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - **Sexual reproduction:** two parents, gametes fuse; each offspring gets a random half of each parent's genes, so offspring **vary**. - **Asexual reproduction:** one parent, no gametes; offspring are **clones**. - Variation helps a population survive a changing environment; asexual reproduction is fast and needs no partner. ## Exit ticket :::keep-together **Why do two offspring of the same parents look different?** {{lines-3}} ::: :::teacher-note **Answer:** Each gets a random one of each parent's two copies of each gene, so each gets a different combination. :::