--- marp: true theme: default html: true --- # Why don't brothers and sisters look the same? Year 9 Biology · Reproduction --- ## Today **We are learning to** in sexual reproduction each offspring gets a random half of each parent's genes, so offspring vary. In asexual reproduction one parent makes genetically identical clones. Variation helps a population survive change; asexual reproduction is fast and needs no partner. - I can explain why offspring of sexual reproduction vary. - I can explain why asexual reproduction makes clones. - I can give an advantage of each. --- ## Why it matters > 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. --- 💬 Discussion ## Engage: predict **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 --- ✍️ Activity ## Explore it {{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fbiology-9%2Freproduction%2Fstep-2&code=widget%3A+cross%0Amode%3A+offspring%0A&fresh=1}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/biology-9/reproduction/?full=step-2#step-2) --- ✅ Check ## What happened? * 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). --- ✅ Check ## Which kind **Sexual or asexual reproduction?** Groups: Sexual · Asexual Two parents · Offspring are clones of the parent · Gametes fuse at fertilisation · No partner needed · Offspring vary · A strawberry plant's runners * 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 --- ✅ Check ## 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 * Answer: Each gets a random one of each parent's two copies of every gene, so each gets a different combination --- ✅ Check ## 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 * Answer: A population from sexual reproduction: some individuals are likely to have genes that resist it --- ✅ Check ## 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 * 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 --- ✅ Check ## Elaborate: which suits? **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 * Answer: Fast cloning while conditions are good; variation before the harsh, changing winter --- ✅ Check ## Elaborate: bananas **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 * Answer: The clones all have the same genes, so if one is vulnerable, every plant is --- ✅ Check ## 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 * Answer: Society needed it: a fruit most Australians eat, and many growers' farms and jobs, were at risk from a disease with no cure --- ✅ Check ## 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 * Answer: It can steer researchers towards other methods as well, such as breeding resistant bananas, and affect whether a GM banana is ever grown --- ## 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. --- ✅ Check ## Exit ticket **Why do two offspring of the same parents look different?** * Each gets a random one of each parent's two copies of each gene, so each gets a different combination.