Question

this passage describes the shell banding trait in cepaea snails: cepaea snails live on land in many parts of europe. the shells of cepaea snails can have different colors and patterns. banded shells have dark bands, or stripes, that spiral around their surfaces. unbanded shells do not have bands. in a group of cepaea snails, some individuals have a banded shell and others have an unbanded shell. in this group, the gene for the shell banding trait has two alleles. the allele for a banded shell (b) is dominant over the allele for an unbanded shell (b). complete the punnett square below to show all possible genotypes of the offspring from a cross between two cepaea snails. b b b bb bb b

Explanation:

Step1: Analyze the Punnett square structure

The top row has alleles \( B \) and \( b \), and the left column has alleles \( B \) and \( b \). We need to fill the remaining cells by combining the row and column alleles.

Step2: Fill the cell for row \( b \) and column \( B \)

When we combine allele \( b \) (from the left column) with allele \( B \) (from the top row), the genotype is \( Bb \).

Step3: Fill the cell for row \( b \) and column \( b \)

Combining allele \( b \) (from the left column) with allele \( b \) (from the top row) gives the genotype \( bb \).

Answer:

The cell in the second row (row with \( b \)) and first column (column with \( B \)) is \( Bb \), and the cell in the second row and second column is \( bb \). So the completed Punnett square cells (from top - to - bottom, left - to - right for the empty cells) are \( Bb \) and \( bb \).