Biology 9700 · AS & A Level · Passage of information from parents to offspring

Passage of information from parents to offspring — practice question

Gregor Mendel, the scientist, examined how stem length varied in the pea plant, Pisum sativum. He published the findings of this study of the trait (characteristic) in 1866. Fig. 2.1 contains a diagram of a pea plant. Mendel noted that the pea plants he cultivated had either tall stems or dwarf (short) stems. In his investigation, he used crosses between pea plants showing these two phenotypes.
(a)[4]

The outcomes of these crosses showed Mendel that tall stems are dominant over dwarf stems in pea plants. It is now known that stem length in pea plants is controlled by one gene with two alleles: - a dominant allele, Le - a recessive allele, le Describe a cross that could be done and explain how the cross results could be examined to find the genotype of a pea plant with a tall stem.

(b(i))[1]

Gibberellin causes a response in plant cells when it attaches to specific receptor molecules. State the term for a molecule, such as gibberellin, that attaches to specific receptor molecules and triggers a response in cells.

(b(ii))[2]

Suggest what the cells in the internode region of the stem, as shown in Fig. 2.1, do in the presence of gibberellin and describe how this response changes the trait investigated by Mendel.

Worked solution & mark scheme

This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Carrying out a test cross” …

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