CAIE IGCSE Biology 17.4.11 Monohybrid Genetic Diagrams
Practise completing one-gene crosses from parental genotypes through gametes to offspring ratios and probabilities.
- Syllabus
- 2026–2028
- Course
- Biology 0610
Exam points
- write valid parental genotypes and the allele carried by each possible gamete
- combine gametes to obtain every possible offspring genotype and phenotype
- calculate 1:1 or 3:1 phenotype ratios and express them as fractions, decimals or percentages
17.4.11—Genetic diagrams to predict question 1
Fig. 2.1 shows a dwarf sunflower and a tall sunflower, Helianthus annuus. The height of the dwarf sunflower is 0.45 m and the height of the tall sunflower is 4.5 m .
not to scale
Dwarf plants like the one in Fig. 2.1 have mutant alleles.
Two tall sunflower plants were crossed. 25\% of the offspring produced were dwarf.
Explain how it is possible for two tall parent plants to have this percentage of dwarf offspring.
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