In order to determine the genotype of a mendalien with black eyes and green skin, you would cross this individual with a(n) individual.

The question is incomplete, the remaining part is:

B=black eyes G=green skin

b=orange eyes g=white skin

a BBgg

b BBGG

c bbgg

d bbGG

e BbGg

The answer is C (bbgg)

Explanation:

This is involving a dihybrid individual with two genes; one for eye color and the other for skin color. According to the question, alleles for black eyes (B) and green skin (G) are respectively dominant over the alleles for orange eyes (b) and white skin (g).

The question tells us that the individual has a black eyes and green skin, which implies that the individual possess/exhibit both dominant traits. Since, allele B and G can mask alleles b and g, dominance can both be expressed in a heterozygotic (different allele) or homozygotic (identical allele) condition, which one cannot know by merely looking at the individual's phenotype.

In order to ascertain whether the individual is homozygous or heterozygous for the dominant trait (black eyes and green skin), the individual is crossed with a homozygous recessive genotype for both genes, which will be (bbgg) in this case. This cross is referred to as TEST CROSS.

This test cross will produce offsprings that are all dominant for the traits if the individual is homozygous (BBGG), while the individual will be said to be heterozygous (BbGg), if any of the offsprings exhibit the recessive traits (white skin, orange eyes).