Question

Imagine you have two pure-breeding lines of canaries, one with yellow feathers and the other with brown feathers. In crosses between these two strains, yellow female x brown male gives only brown sons and daughters, while brown female x yellow male gives only brown sons and yellow daughters. Propose a hypothesis to explain these results.

Answer 1

The results can be explained if the gene that determines color of feathers is located in the Z chromosome.

Step-by-step explanation:

Unlike mammals that have X and Y sex chromosomes, birds have Z and W sex chromosomes. Females are ZW and males are ZZ.

The gene that determines color of feathers has the alleles:

B_ = brown color

bb = yellow color.

1st cross

yellow female x brown male

♀️
`Z^bW` x ♂️
`Z^BZ^B`

Gametes

Female:
`Z^b` ,
`W`

Male:
`Z^B`

F1

• 
  `Z^BZ^b` = brown males

• 
  `Z^BW` = brown females

2nd cross

brown female x yellow male

♀️
`Z^BW` x ♂️
`Z^bZ^b`

Gametes

Female:
`Z^B` ,
`W`

Male:
`Z^b`

F1

• 
  `Z^BZ^b` = brown males

• 
  `Z^bW` = yellow females