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The fork line method can be used by figuring the occurrence of each gene or set of genes to be found in the gamete and then multiplying them together. This can be multiplied by figuring each trait or combination of traits separate for both the male and female or each gene individually regardless of sex.

The product rule states that the probability of two independent events occurring together can be calculated by multiplying the individual probabilities of each event occurring alone.

While the forked-line method is a diagrammatic approach to keeping track of probabilities in a cross, the probability method gives the proportions of offspring expected to exhibit each phenotype (or genotype) without the added visual assistance. Both methods make use of the product rule and consider the alleles for each gene separately. Hence, option (b) is the correct answer.

a. test cross

Test cross is the cross between F₁individual and the recessive parent. This cross is used to check the purity of the genotype, and to know the genotype of the organism. It is not a probability rule. Hence, option (a) is the incorrect option.

c. monohybrid rule

Monohybrid rule is the cross between individuals differing in a single characteristic, that is having different alleles at a single locus. The forked line and probability methods do not make use of the monohybrid rule. Hence, option (c) is the incorrect option

d. sum rule

According to sum rule, of the two mutually exclusive events, the probability of the occurrence of at least one event is the sum of their probabilities individually. The sum rule is not applied to two independently occurring events as in forked line method. Hence, option (d) is the incorrect answer.