Question

Curly wing (CY) shape and stubble bristles (SB) are both recessive lethal alleles (i.e. dominant in terms of wing shape/bristles phenotype, but recessive for lethality). What would be the result (F₁ phenotypic ratios) of a cross between two curly winged, stubble bristle flies? To develop a hypothesis to predict the phenotypic ratio for the F₁ generation consider the following:

What are the genotypes of the parents? _________________

What phenotypic ratio would you predict for the offspring of a cross between two flies with curly wing shape? __________________

and two flies with stubble bristle?__________________

Use a branch diagram to predict the outcome of dihybrid cross between two curly winged, stubble bristle flies.

Answer 1

Curly wing (CY) shape and stubble bristles (SB) are both recessive lethal alleles (i.e. dominant in terms of wing shape/bristles phenotype, but recessive for lethality). What would be the result (F₁phenotypic ratios) of a cross between two curly winged, stubble bristle flies? To develop a hypothesis to predict the phenotypic ratio for the F₁ generation consider the following:

What are the genotypes of the parents? _________________

Set up a test cross: CY x ccyy

Cross with homozygous recessive individual

There are four different crosses possible:

CCYY x ccyy = all CY

CcYY x ccyy = 1 CY: 1 ccY

CCYy x ccyy = 1 CY: 1 Cyy

CcYy x ccyy = 1 CY: 1 Cyy: 1ccY: 1 ccyy

For Stubble bristles:

SB x ssbb

There are four different crosses possible:

SSBB x ccyy = all SB

SsBB x ccyy = 1 SB: 1 ssB

SSBb x ccyy = 1 SB: 1 Sbb

SsBb ccyy = 1 SB: 1 Sbb: 1ssB: 1 ssbb

What phenotypic ratio would you predict for the offspring of a cross between two flies with curly wing shape?

Curly wing shape                            Curly wing shape                 

CcYy                                   x                   CcYy

                                  Genotype results                Phenotype Results

Cc x Cc = ¼ CC; ½ Cc; ¼ cc                           ¾ CC; ¼ cc

Yy x Yy = ¼ YY; ½ Yy; ¼ yy                            ¾ YY; ¼ Yy

Using a Branch diagram to look at Mendel’s Dyhibrid cross between the F1s

and two flies with stubble bristle?__________________

Stubble bristle                                    Stubble bristle                

SsBb                                   x                   SsBb

                                  Genotype results                Phenotype Results

Ss x Ss = ¼ SS; ½ Ss; ¼ ss                           ¾ SS; ¼ ss

Bb x Bb = ¼ BB; ½ Bb; ¼ bb                            ¾ BB; ¼ Bb

Using a Branch diagram to look at Mendel’s Dyhibrid cross between the F1s