Question

In some bees, thin stripes (S) are dominant over thick stripes (s) and black eyes (B) are dominant over gray eyes (b). Complete a dihybrid cross for parents with the genotypes: SsBB × ssBb and answer the following in complete sentences.
Describe how you would set up a Punnett square for this cross.
List the likelihood of each possible offspring genotype.
List the likelihood of each possible offspring phenotype.

Answer 1

Answer:

Genotypic Ration -

SsBB: ssBB: SsBb:ssBb  is 4: 4:4:4

Likelihood of occurrence is  

SsBB: 25 %

ssBB: 25 %

SsBb:25 %

ssBb:25 %

Phenotypic ratio -

thin striped black eye :  thick striped black eye

8 : 8

1: 1

Likelihood of occurrence is  

thin striped black eye :  50%

thick striped black eye : 50%

Explanation:

The genotype of  two parents is SsBB and ssBb

The alleles for cross for parent with genotype SsBB are  SB, SB, sB, SB

The alleles for cross for parent with genotype ssBb are sB, sb, sB, sb

The cross between the two parents is represented by a punnet square as given below -

        SB          SB          sB         sB

sB SsBB SsBB ssBB ssBB

sb SsBb SsBb ssBb ssBb

sB SsBB SsBB ssBB ssBB

sb SsBb SsBb ssBb ssBb

Genotypic ratio

SsBB: ssBB: SsBb:ssBb  is 4: 4:4:4

Likelihood of occurrence is  

SsBB: 25 %

ssBB: 25 %

SsBb:25 %

ssBb:25 %

As given thin stripes (S) are dominant over thick stripes (s) and black eyes (B) are dominant over gray eyes (b).

So the phenotype for genotype of offsping is as follows

SsBB: thin striped black eye

ssBB: thick striped black eye

SsBb: thin striped black eye

ssBb: thick striped black eye

Phenotypic ratio -

thin striped black eye :  thick striped black eye

8 : 8

1: 1

Likelihood of occurrence is  

thin striped black eye :  50%

thick striped black eye : 50%

Answer 2

I think you would do a 2X2 punnet square. And that the SsBB can produce two kinds of gametes which are SB and sb And that the ssBb can produce two kinds of gametes which are sB and sb So there would be 25% SsBB, 25% SsBb, 25% ssBb, and 25% ssbb