← Teacher guides

Teacher guide: Year 10 Biology

Inheritance and evolution. DNA, genes and chromosomes; how meiosis makes every gamete different; predicting offspring with Punnett squares; then variation in a population and natural selection. Concept tutorials with a zoom from body to gene, a live cross board and a beetle population that evolves.

Open the student course

Each lesson works two ways. Students can work through the online tutorial at their own pace (it checks their answers and saves their progress in their browser), or you can teach it to the whole class from the slides, then send students into the tutorial for the Modify and Make steps.

Every lesson guide has plain-language notes, the answers to every check, a solution for every task, and slides and a worksheet for Waypoints Prepare. These guide pages are not linked from student pages, but they are not secret either: keep printed Teacher editions for answers you do not want students to find.

Genetics

DNA, genes and chromosomes, meiosis, and patterns of inheritance (AC9S10U01).

Genetics in 5 minutes (read before teaching this unit)

The idea in plain words

  • DNA is a long molecule that carries the instructions for building and running an organism. It is coiled into chromosomes in the nucleus (46 in human body cells, in 23 pairs: one of each pair from each parent).
  • A gene is a section of DNA that codes for one protein, which affects a characteristic. Different versions of a gene are alleles.
  • Meiosis is the cell division that makes gametes: the pairs separate, and each gamete gets one chromosome from each pair, chosen at random. With 23 pairs there are over 8 million combinations, before crossing over adds more.
  • Each characteristic in the board's examples is controlled by one gene with two alleles. A dominant allele (B) shows whenever it is present; a recessive allele (b) shows only when there are two (bb). The pair of alleles is the genotype; the characteristic you see is the phenotype.
  • A Punnett square shows every way the parents' gametes can combine, so it gives the probability of each genotype, not a guaranteed count.

Where the picture breaks

  • The zoom is not to scale; a real chromosome is far longer than drawn, and genes are scattered with non-coding DNA between them.
  • Single-gene, two-allele, fully dominant traits are the simple case. Eye colour, height and skin colour are controlled by many genes (and affected by environment), so real eye colour does not follow a 3 : 1 rule.
  • The meiosis board shows 3 pairs and leaves out crossing over.

Common misconceptions

  • A gene is the same thing as a trait ("the blue-eyes gene" as if there were one per colour).
  • Dominant alleles are more common, or "stronger", or better.
  • A 3 : 1 ratio means exactly 3 of 4 children will show the dominant trait.
  • Meiosis makes identical gametes.

Investigate in class

Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.

  • Does the number of offspring change how close a Pp × Pp cross comes to 3 : 1? A coin model (heads P, tails p, one coin per parent). Change: offspring (4, 20, pooled class 200). Measure: proportion showing the dominant trait. Keep the same: fair coins, both parents Pp. (Small families wander a long way from 3 : 1.)
  • Does the number of chromosome pairs change how many different gametes you get? A card model. Change: pairs (1, 2, 3). Measure: different gametes in 20 random draws, one card from each pair. Keep the same: number of draws. (Expect 2, 4, 8.)
  • Does the amount of detergent change how much DNA we extract from strawberries? Change: detergent volume. Measure: mass of DNA strands. Keep the same: strawberry mass, salt, volume of cold alcohol, mixing time.

Safety and ethics: methylated spirits is flammable: no flames, keep it capped and cold.

Evolution

Variation in a population and natural selection (AC9S10U02).

Evolution in 5 minutes (read before teaching this unit)

The idea in plain words

  • Individuals in a population vary: measure any characteristic and you get a spread of values. Much of that variation is inherited (genes), some comes from the environment.
  • Natural selection: individuals vary; more are born than survive; those whose characteristics suit the environment are more likely to survive and reproduce; they pass on their alleles; over many generations, the population's characteristics shift.
  • Individuals don't change to suit the environment: the population changes, because survivors have more offspring.
  • Selection needs variation that already exists; new variation comes from mutations and sexual reproduction.

Where the picture breaks

  • The beetles inherit colour as the average of their parents plus a small random change: a simplification of many genes.
  • Birds hunt by colour contrast alone; real predators use more cues, and real selection acts on many characteristics at once.
  • Each generation is a hunt then a breed; real generations overlap.

Common misconceptions

  • Organisms change because they need to ("the beetles turned dark to hide").
  • Individuals evolve during their lifetime.
  • Natural selection creates the variation.
  • The fittest are the strongest, rather than the best suited to that environment.

Investigate in class

Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.

  • Does the background colour change which "prey" survive? A classroom model of the beetle board. Change: background (green or brown cloth). Measure: toothpicks of each colour left after 30 seconds of "bird" picking. Keep the same: number of each colour, time, number of birds.
  • Does food type change which "beak" collects most? A model. Change: food (seeds, rubber bands, marbles). Measure: items each beak tool (peg, spoon, tweezers) collects in 30 seconds. Keep the same: time, amount of food, container.
  • Do leaves from the sunny side of a tree differ in length from the shady side? Environmental variation. Change: side of the tree. Measure: length of 20 leaves from each (graph both spreads). Keep the same: tree, height picked, measuring method.

Safety and ethics: nobody eats the "food". Collect fallen or lower leaves from school grounds, a few per student.