DP Biology Questionbank

In fruit flies (Drosophila melanogaster), grey bodies (b⁺) are dominant to black bodies (b) and normal wings (vg⁺) are dominant to vestigial wings (vg). Homozygous vestigial winged, black bodied flies were crossed with individuals that were heterozygous for both traits. 2300 individuals were counted and the phenotypes observed were recorded as shown.

965 normal wings, grey bodies
944 vestigial wings, black bodies
206 vestigial wings, grey bodies
185 normal wings, black bodies

Which statement is valid?

A. The predicted phenotypic ratio was 9:3:3: 1.

B. There is independent assortment of wings but not body colour.

C. The expected number of vestigial winged, grey bodied flies was 575.

D. The traits are on different chromosomes.

Autosomal genes are located in chromosomes that are not sex chromosomes. The inheritance of autosomal genes is affected by whether the genes are linked or unlinked. Explain the two types of inheritance, using the example of parents that are heterozygous for two genes A and B.

Explain gene linkage and its effects on inheritance.

Explain the reasons for variation in human height.

When the data in the table were used to calculate chi-squared, the calculated value was 0.056. The critical value is 3.84. Explain the conclusion that can be drawn from the calculated and critical values for chi-squared.

To calculate chi-squared, expected values must first be calculated. Assuming that there is no association between the two species, calculate the expected number of quadrats in which both species would be present, showing your working.

State the number of degrees of freedom for this test to determine the critical value of chi-squared.

William Bateson and Reginald Punnett used the sweet pea (Lathyrus odoratus) in genetics studies in the early 20^th century. Pure-breeding plants that produced purple flowers and long pollen grains were crossed with pure-breeding plants that produced red flowers and round pollen grains. The resulting offspring all produced purple flowers and long pollen grains. Two of the F₁ generation plants were crossed. The table shows the ratio of phenotypes in the F₂ generation. 

What is an explanation for these experimental results?

A. Purple flowers and long pollen grains are dominant and the alleles have assorted independently.

B. The genes for flower colour and pollen shape are linked and all plants producing long pollen grains are recombinants.

C. The genes for flower colour and pollen shape are linked and all plants producing red flowers are recombinants.

D. Plants producing purple flowers and round pollen grains arose through crossing over.