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

Passage of information from parents to offspring — practice question

In the sweet pea plant, Lathyrus odoratus, one gene determines flower colour and a different gene determines pollen grain shape. Flowers may be purple or red. Pollen grains may be long or round. The inheritance of these genes is an example of autosomal linkage. The allele F for purple flowers is dominant over the allele f for red flowers. The allele G for long pollen grains is dominant over allele g for round pollen grains.
(a)[2]

Explain what is meant by the term autosomal linkage.

(b(i))[4]

Draw a genetic diagram to show a dihybrid cross between two offspring from the F1 generation. Assume that these genes are closely linked and that no crossing over takes place.

(b(ii))[1]

State how the results demonstrate that this is an example of autosomal linkage.

(c(i))[1]

In a test cross, an individual with a known genotype is crossed with an individual that shows the dominant phenotype but has an unknown genotype. State the genotype of the known individual in a test cross.

(c(ii))[1]

Calculate the crossover value (COV) from the results in Table 2.2. The crossover value (COV) is found using the formula $\text{COV} = \frac{\text{number of recombinants}}{\text{total number of individuals}} \times 100$.

(c(iii))[1]

Suggest what information crossover values can provide about the relative distance between linked genes.

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