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CAIE IGCSE Biology 17.4.2 Genotype & Alleles

Practise defining genotype as an organism's genetic make-up and writing it using the alleles present.

Syllabus
2026–2028
Course
Biology 0610

Exam points

  • define genotype in terms of the combination of alleles carried by an organism
  • use consistent dominant and recessive symbols to write possible genotypes
  • deduce an unknown genotype from offspring or parental-cross evidence

17.4.2—Genotype as the genetic make-up question 1

[Maximum number: 6]

The garden pea, Pisum sativum, is a plant which has flowers that have both male and female parts. P. sativum is naturally self-pollinating.

Question (a)

(a)

Gregor Mendel studied inheritance in the garden pea, P. sativum.

The flowers of P. sativum that he studied were either purple or white. The gene that controls flower colour has two alleles, B and b.

When Mendel crossed purple-flowered plants with white-flowered plants all the plants in the next generation had purple flowers.

[ 4 ]

Question (i)

(i)

Table 4.1 shows five genetic terms that can be applied to Mendel's study of the inheritance of flower colour.

Complete Table 4.1 by stating an example of each genetic term. The first one has been completed for you.

Table 4.1

Table 4.1

[ 4 ]

Question (b)

(b)

Pickerel weed, Pontederia cordata, is a plant that grows in shallow water on the edges of ponds and lakes in North America.

A few seedlings of these plants are white. The white seedlings cannot make chlorophyll.
Researchers carried out several crosses using pickerel weed plants.

Their results are shown in Table 4.2.

Table 4.2

Table 4.2

[ 2 ]

Question (i)

(i)

Select suitable symbols for the alleles and state the possible genotypes of the parents for each cross.
cross 1
cross 2

[ 2 ]
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