BrainteenAges 15–17ScienceWorksheet

Genetic crosses: Punnett squares and probability (GCSE-style Higher (grades 8–9))

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Show your working and give units. Magnification = image size ÷ actual size (both in the same unit: 1 mm = 1000 µm, 1 µm = 1000 nm). Where an answer is not exact, round it as the question says.

1.A couple have a baby. What is the probability that the baby is a girl? Give your answer as a fraction.

2.In mice, the allele for brown fur is dominant and the allele for white fur is recessive. Two parents with genotypes Bb and Bb are crossed. The parents have two offspring. What is the probability that both show white fur? Give your answer as a fraction.

3.In fruit flies, the allele for normal wings is dominant and the allele for short wings is recessive. Two parents with genotypes Nn and Nn are crossed. What is the expected ratio of dominant to recessive phenotypes in the offspring?

1 : 11 : 23 : 11 : 3

4.In pea plants, the allele for tall stems is dominant and the allele for short stems is recessive. Two parents with genotypes Tt and tt are crossed. What is the probability that an offspring is heterozygous? Give your answer as a fraction.

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Show your working and give units. Magnification = image size ÷ actual size (both in the same unit: 1 mm = 1000 µm, 1 µm = 1000 nm). Where an answer is not exact, round it as the question says.

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About this activity

What your child practises

Practising key skills with a ready-to-use activity.

What’s included

10 questions
An answer key you can print with the sheet or on its own
An on-screen version with instant marking and stars

Age and school year

Made for ages 15–17. That’s Grade 10–12 in the US, Year 11–13 in England, SS 1–3 in Nigeria and Class 10–12 in India.

How to use it

Print it at home or school – it fits a standard A4 or US Letter page.
Print the answer key too, so marking takes seconds.
Play it on screen: answers are marked instantly and children earn stars.
Write on it on a tablet or touchscreen with a finger or stylus – no printer needed.

Tips for parents and teachers

Little and often wins: five minutes a day beats one long session a week.
Do it on screen first for instant marking, then print it a few days later to see what was remembered.
Combine this sheet with past exam questions on the same topic for mixed, exam-style practice.

Good to know

Time needed: About 15–25 minutes
You’ll need: A printer (or a tablet to work on screen), a pencil and an eraser
Difficulty: Expert (GCSE-style Higher (grades 8–9)) – pitched at ages 15–17
Answer key: Yes – print it with the sheet or on its own

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