"labrador retrievers come in three colors: black, brown, and yellow. coat color among labradors arises through the interaction between the alleles of two genes. one gene produces melanin. allele b (black) is dominant to allele b (brown). another gene, a regulatory gene, affects the deposition of pigment in individual hairs. allele e promotes the deposition but in the recessive homozygote (ee) the gene blocks deposition and a yellow coat results. what are the phenotypic ratios of the f1 generation offspring of two dihybrids

4/16 yellow Labradors, 9/16 black Labradors and 3/16 brown Labradors.

Explanation: Two dihybrids would have BbEe alleles. Using Mendel's chess table of independent segregation to show the offspring,  we have the following results:

BBee - 1/16 - yellow

BBEe - 2/16 - black

BBEE - 1/16 - black

BbEe - 4/16 - black

Bbee - 2/16 - yellow

BbEE - 2/16 - black

bbEe - 2/16 - brown

bbEE - 1/16 - brown

bbee - 1/16 - yellow

If the offspring presents B_E_ phenotypes, it will have black pigment deposition. If the offspring presents bbE_ phenotypes, it will have brown pigment deposition. Otherwise, if it presents _ _ee phenotypes, there won't be any pigment deposition, therefore they are yellow.

Adding up all the phenotypes ratios, we have 4/16 yellow Labradors, 9/16 black Labradors and 3/16 brown Labradors.

i think its the first one

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.