In pigs, several alleles exist for the gene POLR1B. A pig breeder arranged several matings between a group of pigs in his operation who were all heterozygous with two different alleles for the POLR1B gene (both were ‘Pp’). Individuals who are PP are black in color while heterozygous individuals (Pp) are grey. Homozygous recessive individuals (pp) are white. Below is the result of this cross Parental generation Pp x Pp F1: Black: 17 piglets Grey: 33 piglets Which of the following are possible explanations for the pattern we see in the F1 generation. Group of answer choices

a. Embryonic lethality: homozygous recessive individuals didn’t survive
b. Standard Mendelian ratio 3:1 (dominant to recessive)
c. Codominance (neither the black nor the white allele is completely dominant).
d. Both a and c above are supported by the evidence.