📚 Part 1: Multiple Choice Answers
1. What is a gene?
A type of cell
✓
A section of DNA that codes for a trait
A chromosome
A protein
Explanation: A gene is a specific sequence of DNA that contains instructions for making proteins, which determine our traits.
2. In a monohybrid cross Bb × Bb, what is the probability of offspring being homozygous recessive?
Explanation: Using a Punnett square: BB, Bb, Bb, bb. Only 1 out of 4 offspring (25%) will be bb (homozygous recessive).
3. Which of the following are examples of inherited traits? (Select all that apply)
✓
Eye colour
Scars from accidents
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Blood type
Language spoken
✓
Height potential
Explanation: Inherited traits are passed from parents through genes. Scars and language are acquired, not inherited.
4. What does heterozygous mean?
Having two identical alleles
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Having two different alleles for a trait
Having no alleles
Having extra chromosomes
Explanation: Heterozygous means having two different versions (alleles) of the same gene, like Bb.
✏️ Part 2: Problem Solving Answers
5. Corrected Dihybrid Cross Problem: In guinea pigs, brown coat (B) is dominant over white coat (b), and short hair (S) is dominant over long hair (s). Cross a heterozygous brown, short-haired guinea pig (BbSs) with a white, short-haired guinea pig (bbSs). What percentage of offspring will have brown coat and long hair?
Answer: 12.5%
Working:
Cross: BbSs × bbSs
Gametes from BbSs: BS, Bs, bS, bs
Gametes from bbSs: bS, bs
Offspring with brown coat and long hair = Bbss
Probability = 1/8 = 12.5%
Phenotypic ratio:
Brown short: 3/8 (37.5%)
Brown long: 1/8 (12.5%)
White short: 3/8 (37.5%)
White long: 1/8 (12.5%)
6. Explain the difference between genotype and phenotype using an example.
Genotype: The genetic makeup (letters/alleles) of an organism
Phenotype: The observable physical characteristics
Example: For eye colour in humans:
Genotype: BB or Bb (brown eyes), bb (blue eyes)
Phenotype: Brown eyes or blue eyes (what you see)
7. A plant with red flowers (RR) is crossed with a plant with white flowers (WW). If the offspring show pink flowers, what type of inheritance is this?
Answer: Incomplete dominance
Explanation: In incomplete dominance, neither allele is
completely dominant. The heterozygous offspring (RW)
show a blended phenotype (pink flowers) that is
intermediate between the two parent phenotypes.
🎯 Success Criteria & Extension Activities
Success Criteria - Students can:
✓ Define key genetic terms (gene, allele, genotype, phenotype)
✓ Distinguish between dominant and recessive traits
✓ Use Punnett squares to predict inheritance patterns
✓ Calculate probabilities and percentages for genetic crosses
✓ Explain different types of inheritance (complete, incomplete dominance)
Extension Activity for Advanced Learners:
Research a genetic disorder that follows Mendelian inheritance
(e.g., cystic fibrosis, sickle cell anaemia). Create a family
pedigree showing how the condition is inherited and
calculate the probability of affected offspring in different
scenarios. Present your findings to the class.
Support for Diverse Learners:
• Use visual aids and colour-coding for Punnett squares
• Provide step-by-step worked examples
• Use familiar examples (pet traits, human characteristics)
• Allow collaborative work for complex problems
• Offer alternative assessment formats (oral, visual)
