MYP Biology: Inheritance & Genetics (MYP 4-5) FAQ

Genetics is tricky because it layers three skills at once: abstract vocabulary (allele, genotype, phenotype), symbolic notation (Punnett squares), and probability. Students who are fine with cells or ecosystems often stall here because there's no diagram to look at — you have to hold the logic in your head.

A dominant allele shows up in the phenotype even when only one copy is present (one capital letter, e.g. B). A recessive allele only shows in the phenotype when two copies are present (bb) — with one dominant and one recessive present, the dominant trait masks the recessive one.

Punnett squares confuse students because the grid itself is easy but labelling the parent gametes correctly is where marks are lost. Each parent contributes one allele per box, not their whole genotype — mixing that up gives wrong ratios even when the grid is drawn perfectly.

Genotype is the genetic makeup written as letters (BB, Bb, bb) — it's what's inside the DNA. Phenotype is the observable trait that genotype produces — eye colour, height, blood type. Genotype is the code; phenotype is what you can actually see or measure.

Homozygous means both alleles for a trait are identical — either BB (homozygous dominant) or bb (homozygous recessive). Heterozygous means the two alleles differ, like Bb — one dominant, one recessive. The prefix gives it away: homo = same, hetero = different.

A pedigree chart tracks how a trait passes through generations of a family using squares (male) and circles (female), shaded to show who has the trait. MYP tasks use them because they test Criterion A (knowledge) and Criterion C (communication) together — you have to read the diagram and explain the pattern in words.

DNA is the molecule that stores genetic information. A gene is a specific section of DNA coding for one trait. Chromosomes are structures made of tightly coiled DNA, and humans have 23 pairs. So the order runs: DNA to gene to chromosome to trait — each level packages the one below it.

Top marks in a genetics task come from precision, not extra content: correct genotype notation, a fully labelled Punnett square, and a conclusion that links the ratio back to the biological question asked. Level 7-8 responses explain why the ratio occurs, not just what it is.

Practise the same cross type repeatedly until the 3:1 and 1:1 ratios feel automatic, then move to trickier crosses like test crosses (Bb x bb) and incomplete dominance. Timed, low-stakes repetition beats reading notes — genetics is a procedural skill, closer to maths than to memorising facts.

MYP inheritance work (alleles, dominant/recessive, Punnett squares) is the direct foundation for DP Biology's genetics topic, which adds meiosis detail, pedigree probability calculations and Hardy-Weinberg population genetics at HL. Students who master MYP-level notation move through DP genetics noticeably faster.

Genetics is unusually abstract compared to topics like ecosystems or human body systems — there's often no physical diagram to anchor understanding, just symbols and ratios. A student who's strong at descriptive biology can genuinely struggle here until they've had repeated, structured practice with Punnett squares specifically.

Structured, topic-specific practice tends to help more than re-reading a textbook chapter, since genetics is a procedural skill built through repetition. On revisionprep.com, MYP Biology Revision Notes and Topical Worksheets break inheritance into single-gene crosses, pedigree charts and terminology drills your child can work through independently.