# Modified Mendelian Ratios Problem

I'm studying modified Mendelian ratios. I've got a theoretical problem that I'm stumped on:

A species of bird may have normal wings, or a mutation that causes frazzled wings.

I do 15 identical breeding pairs, crossing a male bird with frazzled wings to a normal winged female. The progeny obtained are 46 with normal wings (22 male/24 female) and 23 frazzled, all male.

Afterwards, I mate the normal winged females to the normal winged males obtained from the above cross. The progeny obtained all have normal wings.

I figured out a possible solution, and would like to know if it makes sense:

Z(f) = Z sex chromosome with normal wing gene, recessive
Z(F) = Z sex chromosome with frazzled wing gene, dominant
W = W sex chromosome

• Z(F)/W = abnormal wing female bird (does not survive as not enough gene product produced)
• Z(f)/W = normal wing female bird
• Z(F)/Z(F) = abnormal wing male bird (does not survive as not enough gene product produced, or possibly survives as just enough is produced by 2 mutant genes, doesn't matter anyway)
• Z(F)/Z(f) = abnormal wing male bird (survives as wildtype gene produces enough product)
• Z(f)/Z(f) = normal winged male bird

My crosses:

P1: Z(F)/Z(f) × Z(f)/W
Progeny: Z(F)/Z(f), Z(f)/Z(f), Z(F)/W (fails to survive), Z(f)/W

F1: Z(F)/Z(f), Z(f)/Z(f), Z(f)/W in 2:1 normal:frazzled wings
F2: Z(f)/Z(f) × Z(f)/W produces Z(f)/Z(f), Z(f)/W

This would account for the phenotypic ratios seen in the problem, and also uses the ZW sex chromosome system found in birds. The genetic explanation would be that a single Z(F) does not produce enough product to thrive, for whatever reason. The trait is sex-linked dominant on the Z chromosome.

• Can you shorten your question. Just keep the latest part that you want to ask with minimum required background. – WYSIWYG Dec 5 '14 at 8:27