A student whose hobby was fishing pulled a very unusual carp out of Cayuga Lake: It had no scales on itsbody. She decided to investigate whether this strangenude phenotype had a genetic basis. She therefore obtained some inbred carp that were pure-breeding forthe wild-type scale phenotype (body covered withscales in a regular pattern) and crossed them with hernude fish. To her surprise, the F1 progeny consistedof a 1:1 ratio of wild-type fish and fish with a singlelinear row of scales on each side.a. Can a single gene with two alleles account for thisresult? Why or why not?b. To follow up on the first cross, the student allowedthe linear fish from the F1 generation to mate witheach other. The progeny of this cross consisted offish with four phenotypes: linear, wild type, nude,and scattered (the latter had a few scales scattered irregularly on the body). The ratio of these phenotypeswas 6:3:2:1, respectively. How many genes appear tobe involved in determining these phenotypes?c. In parallel, the student allowed the phenotypicallywild-type fish from the F1 generation to mate witheach other and observed, among their progeny, wildtype and scattered carp in a ratio of 3:1. How manygenes with how many alleles appear to determinethe difference between wild-type and scattered carp?d. The student confirmed the conclusions of (c) bycrossing those scattered carp with her purebreeding wild-type stock. Diagram the genotypesand phenotypes of the parental, F1, and F2 generations for this cross and indicate the ratios observed.e. The student attempted to generate a true-breedingnude stock of fish by inbreeding. However, shefound that this was impossible. Every time shecrossed two nude fish, she found nude and scattered fish in the progeny, in a 2:1 ratio. (The scattered fish from these crosses bred true.) Diagramthe phenotypes and genotypes of this gene in anude × nude cross and explain the alteredMendelian ratio.f. The student now felt she could explain all of herresults. Diagram the genotypes in the linear × linear cross performed by the student in (b). Show thegenotypes of the four phenotypes observed amongthe progeny and explain the 6:3:2:1 ratio.
A student whose hobby was fishing pulled a very unusual carp out of Cayuga Lake: It had no scales on its
body. She decided to investigate whether this strange
nude phenotype had a genetic basis. She therefore obtained some inbred carp that were pure-breeding for
the wild-type scale phenotype (body covered with
scales in a regular pattern) and crossed them with her
nude fish. To her surprise, the F1 progeny consisted
of a 1:1 ratio of wild-type fish and fish with a single
linear row of scales on each side.
a. Can a single gene with two alleles account for this
result? Why or why not?
b. To follow up on the first cross, the student allowed
the linear fish from the F1 generation to mate with
each other. The progeny of this cross consisted of
fish with four
and scattered (the latter had a few scales scattered irregularly on the body). The ratio of these phenotypes
was 6:3:2:1, respectively. How many genes appear to
be involved in determining these phenotypes?
c. In parallel, the student allowed the phenotypically
wild-type fish from the F1 generation to mate with
each other and observed, among their progeny, wildtype and scattered carp in a ratio of 3:1. How many
genes with how many alleles appear to determine
the difference between wild-type and scattered carp?
d. The student confirmed the conclusions of (c) by
crossing those scattered carp with her purebreeding wild-type stock. Diagram the genotypes
and phenotypes of the parental, F1, and F2 generations for this cross and indicate the ratios observed.
e. The student attempted to generate a true-breeding
nude stock of fish by inbreeding. However, she
found that this was impossible. Every time she
crossed two nude fish, she found nude and scattered fish in the progeny, in a 2:1 ratio. (The scattered fish from these crosses bred true.) Diagram
the phenotypes and genotypes of this gene in a
nude × nude cross and explain the altered
Mendelian ratio.
f. The student now felt she could explain all of her
results. Diagram the genotypes in the linear × linear cross performed by the student in (b). Show the
genotypes of the four phenotypes observed among
the progeny and explain the 6:3:2:1 ratio.
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