Question

In rats, the genes B and D control fur color as follows: B_dd rats have black fur, bbD_ have yellow fur, B_D_ have brown fur, and bbdd rats have cream-colored fur. If a pure-breeding brown rat and a pure-breeding cream-colored rat mate to produce an F1, and F1 are allowed to interbreed to produce an F2, what is the expected phenotypic distribution of the brown fur color rat offspring

Answer 1

Phenotypes:

• 9/16 Brown-fured rats, B-D-
• 3/16 Black-fured rats, B-dd
• 3/16 Yellow-fured rats, bbD-
• 1/16 Cream-fured rats, bbdd

Step-by-step explanation:

Available data:

• the genes B and D control fur color
• B_dd rats have black fur,
• bbD_ have yellow fur,
• B_D_ have brown fur,
• bbdd rats have cream-colored fur

1st cross: pure-breeding brown rat with a pure-breeding cream-colored rat

Parentals) BBDD x bbdd

Gametes) BD, BD, BD, BD

bd, bd, bd, bd

F1) 100% BbDd

2nd Cross: F1 individuals interbreed

Parentals) BbDd x BbDd

Gametes) BD, Bd, bD, bd

BD, Bd, bD, bd

Punnett square) BD Bd bD bd

BD BBDD BBDd BbDD BbDd

Bd BBDd BBdd BbDd Bbdd

bD BbDD BbDd bbDD bbDd

bd BbDd Bbdd bbDd bbdd

F2) Genotypes:

• 1/16 BBDD
• 2/16 BBDd
• 1/16 BBdd
• 2/16 BbDD
• 4/16 BbDd
• 2/16 Bbdd
• 1/16 bbDD
• 2/16 bbDd
• 1/16 bbdd

Phenotypes:

• 9/16 Brown-fured rats, B-D-
• 3/16 Black-fured rats, B-dd
• 3/16 Yellow-fured rats, bbD-
• 1/16 Cream-fured rats, bbdd