Six original Cambridge-style questions on genetic vocabulary, complete genetic diagrams, ratios and probabilities from Punnett squares and using a test cross to find an unknown genotype.
Define (a) genotype, (b) homozygous, (c) heterozygous and (d) recessive allele.
In tomato plants, red fruit (R) is dominant to yellow fruit (r). Two heterozygous plants are crossed. Draw a complete genetic diagram and state the expected ratio of the offspring phenotypes.
A heterozygous red-fruited tomato plant (Rr) is crossed with a yellow-fruited plant (rr). 120 seeds grow into plants. (a) State the expected phenotype ratio. (b) Calculate the expected number of yellow-fruited plants. (c) State the probability that one particular seed grows into a red-fruited plant.
Explain why a plant that is homozygous for an allele is pure-breeding, but a heterozygous plant is not.
Extended. Purple flowers (P) are dominant to white flowers (p). Explain how a test cross could show whether a purple-flowered plant is PP or Pp.
Two pure-breeding pea plants, one with green pods and one with yellow pods, were crossed. All the F1 plants had green pods. Two F1 plants were then crossed, giving 580 plants with green pods and 202 with yellow pods. (a) State which allele is dominant. (b) Calculate the ratio green : yellow to one decimal place. (c) State the genotype of the F1 plants, using G and g.
Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.