Colored protein granules in the kernels of corn is due to the dominant allele R. The recessive allele r, when homozygous, produces colorless protein granules. Leaf color is controlled by another gene with two alleles, Y and y. The dominant allele Y results in green color, whereas the homozygous presence of the y allele causes leaves to appear yellow. In a testcross between a plant of unknown genotype and phenotype and a plant that is homozygous recessive for both traits, the following progeny were obtained:

Colored, green: 88

Colored, yellow: 12

Colorless, green: 8

Colorless, yellow: 92

a) What was the genotype of the unknown individual? Give it in linkage notationb) What was the phenotype of the unknown individual?

Answer: a) RY/ry

b) The unknown individual has colored protein granules and green colored leaves.

Explanation: a) Examining the progeny, we have individuals that are colored and green, which are the dominant gene of each trait. Since one of the parents is homozygous recessive, to "create" an offspring with those characteristics (color and green), the unknown parent must have at least one dominant allele of each: R and Y. There are also, individuals with the recessive trait, so the unknown parent must be heterozygous for both characteristics. In short, the unknown parent is RrYy.

There are 3 ways of showing linkage notation:

1) Two lines: each one representing a chromosome and showing the corresponding gene;

2) One line: genes on the same side are on the same chromosome;

3) Slash: genes on the same side are on the same chromosome:

So, the representation of the unknown parent is: RY/ry

b) The phenotype of the individual is a plant which has colored protein granules and green colored leaves