The ratio $1:1:1:1$ is observed in:

The Mendel dihybrid phenotypic ratio is . . . . . . .

When a pure tall pea plant with green pods is crossed with a dwarf plant with yellow pods, how many $F_2$ offspring out of $16$ will be tall?

How many different kinds of gametes may be produced by an organism with the genotype $RrYy$?

$A$ diploid organism is heterozygous for $4$ loci. How many types of gametes can be produced?

In Duroc-Jersey hogs,skin color is determined by two pairs of alleles,$R/r$ and $S/s$. Any genotype containing at least one dominant $R$ allele and one dominant $S$ allele results in a red skin color. $A$ double recessive genotype $(rrss)$ results in a white skin color. All other genotypes result in a sandy skin color. If a Duroc-Jersey hog with the genotype $RrSs$ is crossed with a hog having the genotype $rrss$,what will be the phenotypic ratio of the offspring?