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

Passage of information from parents to offspring — practice question

The summer squash plant, $\u001a\textit{Cucurbita pepo}$, bears edible fruits that occur in different shapes. Fig. 2.1 shows the fruits of three squash varieties. In squash plants, fruit shape is controlled by two genes, $A/a$ and $B/b$, which are found on different chromosomes. • A disc-shaped fruit is formed when both dominant alleles, $A$ and $B$, are present. • A spherical fruit is formed when either allele $A$ or allele $B$ is present, but not when both $A$ and $B$ are present. • A long fruit is formed when both allele $A$ and allele $B$ are absent.
(a(i))[1]

Table 2.1 gives the possible genotypes of the Patty pan and Alfresco varieties. Complete Table 2.1 by showing the possible genotypes of the Di Nizza variety.

(a(ii))[4]

A gardener used pollen from a male flower of Alfresco to pollinate a female flower of Di Nizza. The seeds from this cross were grown, and it was found that half the offspring formed spherical fruits and half formed long fruits. Draw one genetic diagram to explain this result. Include parent genotypes, gametes, offspring genotypes and offspring phenotypes.

(a(iii))[2]

The offspring show genetic variation in the alleles for fruit shape. Name the process that happened during meiosis in the parents and produced this variation, and state the stage of meiosis at which it occurred.

(b(i))[2]

Since 1995, genetically modified (GM) summer squash plants with resistance to viral diseases have been grown in the USA. Scientists have worried that viral resistance genes may pass readily from GM squash plants to their wild relative, the Texas gourd, $\u001a\textit{Cucurbita texana}$. Explain why the possibility of gene flow from GM squash plants to the Texas gourd is a source of social and environmental concern.

(b(ii))[2]

Discuss whether these results support the use of genetically modified organisms (GMOs) in food production.

(b(iii))[1]

Suggest why the GM virus-resistant squashes grown by farmers are rarely infected by $\u001a\textit{Erwinia}$.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The correct genotypes are AAbb, Aabb, aaBB, aaBb” …

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