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Biology µGCSE:

Monohybrid Inheritance




10 minutes maximum! (can you do it in 5?)

Q1-2. Maize seeds can have a variety of colours and shapes:

Maize Plant Maize plants

Maize Fruit Corn on the Cob
Maize fruits – corn on the cob: The cobs contain hundreds of seeds

Pollen from a pure breeding plant that produces purple seeds is used to fertilize ovules on a plant that was grown from a yellow seed. The seeds produced from the cross are grown, and all the ‘corn on the cobs’ produced were purple.

1. Which is the dominant allele?
  • A. Yellow
  • B. Purple
  • C. Both yellow and purple
  • D. Neither purple or yellow.
2. The purple seeds from the first cross were planted. When these heterozygous plants were mature they were crossed with each other. What would be the ratio of purple to yellow seeds on the corn cobs?
  • A. 3 yellow : 1 purple
  • B. 1 yellow: 1 purple
  • C. 1 yellow: 3 purple
  • D all purple

3-5: White rabbits lack pigment in their hair and in their skin. They are called albino.

Albinism is caused by a recessive allele a. The dominant allele A causes the rabbit to have normal pigmentation and be brown.

  Albino Rabbit
3. What is the genotype of an albino rabbit?
  • A. AA
  • B. Aa
  • C. aa
  • D. aA
4. Two rabbits heterozygous for fur colour mate and produce several offspring.

What proportion of the offspring are expected to be albino?

  • A. 25%
  • B. 50%
  • C. 75%
  • D. 100%
5. What proportion of the offspring will be homozygous dominant for brown fur?
  • A. 100%
  • B. 75%
  • C. 50%
  • D. 25%

6-10: Cystic fibrosis is an inherited disorder that affects the lungs and the gut. It is carried on a recessive allele.

    Here is a family pedigree for a family with carriers of cystic fibrosis:

    Family tree cycstic fibrosis

6. What is the probability that Sam has cystic fibrosis?
  • A. 0%
  • B. 25%
  • C. 50%
  • D. 100%
7. What is the probability that Sam’s sister will be a carrier for cystic fibrosis?
  • A. 0%
  • B. 25%
  • C. 50%
  • D. 100%
8. What is Jane’s phenotype?
  • A.  female but not a carrier
  • B.  female with cystic fibrosis
  • C.  carrier female
  • D. female but may or may not be a carrier

9. The allele for cystic fibrosis may have been caused by a mutation. A mutation is ...

  • A. a frequent random change in the DNA that can be inherited.
  • B. a rare random change in the DNA that cannot be inherited.
  • C. always bad, causing harm to the organism.
  • D. a rare random change in the DNA that can be inherited.
10. Which of the following is unlikely to cause a mutation?
  • A. u/v radiation
  • B. caffeine
  • C. nicotine
  • D. X-rays