Question

Hereditary Patterns

Answer 1

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 2

First identify the gametes each parent can produce.

SsBB parent can product SB and sB

ssBb parent can produce sB and sb

The punnet square looks like this, fill it in.



Notice how this is simpler than most dihybrid crosses because each parent produces only 2 different gametes.

To find the probabilities (likelyhood) of any one offspring genotype you can divide the frequency of the genotype in question by all of the possible genotypes.

To find the phenotype (what they look like) you first have to determine what that is - by using the genotype and the hierarchy of dominant genes and the products they express.

For example, if you have a genotype SsBB, then the offspring will have thin stripes (because S is dominant over s) and it will have black eyes (because B gene is present).