Question

In a certain flowering plant long leaves are dominant to short, and purple petals are dominant to white. The leaf length gene and the petal color gene are linked. A cross is conducted: Ll Pp X ll pp. If no crossing over occurs, which phenotypic ratio is expected?

a. 9:3:3:1
b. 1:1:1:1
c. 3:1:1:3
d. 1:2:1:2

Answer 1

The expected phenotypic ratio for a cross between Ll Pp and ll pp, when no crossing over occurs and the genes are linked, is 1:1:1:1, yielding equal proportions of parental phenotypes.

Step-by-step explanation:

The expected phenotypic ratio for a cross Ll Pp X ll pp when no crossing over occurs and genes are linked would be 1:1:1:1. This situation refers to the inheritance of two traits together because the genes for leaf length and petal color are located close to each other on the same chromosome and do not assort independently. In the cross between a heterozygous plant (Ll Pp) and a homozygous recessive plant (ll pp), the progeny will be a mix of the two parental types in equal proportions since there's no crossing over to provide new combinations. In the absence of crossing over, the offspring types and expected phenotype ratio are as follows:

• Ll Pp - Long leaves with purple petals
• ll pp - Short leaves with white petals

With each parental type having an equal chance of being produced, this results in a 1:1:1:1 phenotypic ratio.