Question

referring to the punnett square below, what is the genotype and phenotype of the square marked with \x\? (aks 7e)
punnett square and answer choices as shown in the image

Explanation:

Step1: Determine the genotype of X

To find the genotype of the square marked "X" in the Punnett square, we look at the row and column headers for that square. The row header is "pr" and the column header is "Pr".
- The row (pr) contributes the alleles \( p \) and \( r \).
- The column (Pr) contributes the alleles \( P \) and \( r \).

When we combine these alleles, we get the genotype by taking one allele from the row and one from the column for each gene. For the first gene (controlling lip puffiness/thinness): \( p \) (from row) and \( P \) (from column) give \( Pp \)? Wait, no, wait. Wait, the row is "pr" (so the two alleles for the two genes are \( p \) and \( r \)) and the column is "Pr" (alleles \( P \) and \( r \))? Wait, no, actually, in a Punnett square for two genes (dihybrid cross), each cell is the combination of one allele from the top (female gametes) and one from the side (male gametes) for each gene.

Wait, let's re - examine the Punnett square structure. The top headers are the female gametes: PR, Pr, pR, pr. The side headers are the male gametes: PR, Pr, pR, pr. Wait, no, the original Punnett square has top as PR, Pr, pR, pr (maybe female gametes) and side as PR, Pr, pR, pr (male gametes). Wait, the square marked "X" is in the row with side header "pr" and column with top header "Pr".

So the female gamete (top) is "Pr" which means the alleles are \( P \) and \( r \), and the male gamete (side) is "pr" which means the alleles are \( p \) and \( r \).

For the first gene (P/p): female gives \( P \), male gives \( p \), so the genotype for the first gene is \( Pp \)? Wait, no, wait the options have genotypes like pprr, PPRR, etc. Wait, maybe I misread the row and column. Wait, looking at the other cells in the same row (row with side header "pr"): the cells are PPRr, PPrr, X, Pprr? Wait, no, the row with side header "pr" has cells: PPRr (first column, top header PR), PPrr (second column, top header Pr), X (third column, top header pR? Wait, no, the top headers are PR, Pr, pR, pr (from left to right). The side headers are PR, Pr, pR, pr (from top to bottom). Wait, the square "X" is in the third column (top header pR) and fourth row (side header pr)? Wait, maybe I made a mistake in the row and column. Let's list the cells:

Looking at the Punnett square:

- Top row (PR) and side row (PR): PPRR
- Top row (PR) and side row (Pr): PPRr
- Top row (PR) and side row (pR): PPRR
- Top row (PR) and side row (pr): PPRr
- Top row (Pr) and side row (PR): PPRr
- Top row (Pr) and side row (Pr): PPrr
- Top row (Pr) and side row (pR): PPrr
- Top row (Pr) and side row (pr): PPrr? No, that's not matching. Wait, the square "X" is in the column with top header "pR" and row with side header "pr"? Wait, no, the user's Punnett square:

The columns (top) are PR, Pr, pR, pr (left to right). The rows (side) are PR, Pr, pR, pr (top to bottom).

The cell "X" is in the row (side) "pr" and column (top) "Pr"? Wait, no, looking at the cells:

First row (side PR):

- Column PR: PPRR
- Column Pr: PPRr
- Column pR: PPRR
- Column pr: PPRr

Second row (side Pr):

- Column PR: PPRr
- Column Pr: PPrr
- Column pR: PPrr
- Column pr: PPrr

Third row (side pR):

- Column PR: PPRR
- Column Pr: PPRr
- Column pR: PpRr? No, the cells are PPRR, PPRr, PpRr, Pprr? No, the given cells in the third row (side pR) are PPRR, PPRr, PpRr, Pprr? Wait, no, the original Punnett square as per the image:

Wait, the third row (side pR) has cells: PPRR (column PR), PPRr (column Pr), PpRr (column pR), Pprr (column pr)? And the fourth row (side pr) has cells: PPRr (column PR), PPrr (column Pr), X (column pR), Pprr (column pr).

Wait, no, the square "X" is in the row with side header "pr" and column with top header "pR". So the female gamete (top) is "pR" (alleles \( p \) and \( R \)) and the male gamete (side) is "pr" (alleles \( p \) and \( r \)).

So for the first gene (P/p): female gives \( p \), male gives \( p \), so \( pp \).

For the second gene (R/r): female gives \( R \), male gives \( r \), so \( Rr \).

So the genotype of X is \( ppRr \)? Wait, no, the options have A: ppRr; thin and red lips, B: PPRR; puffy and red lips, C: pprr; thin and purple lips, D: pprr; puffy and purple lips. Wait, maybe I messed up the row and column. Let's re - evaluate.

Wait, the key is to look at the pattern of the other cells. Let's look at the row where the side header is "pr" (fourth row). The cells in this row are:

- Column PR: PPRr
- Column Pr: PPrr
- Column pR: X
- Column pr: Pprr

Wait, no, the fourth row (side pr) and third column (top pR). Let's take the alleles from the top (pR) and side (pr). Top (pR) has alleles \( p \) and \( R \), side (pr) has alleles \( p \) and \( r \).

Combining for the first gene (P/p): \( p \) (top) and \( p \) (side) → \( pp \).

Combining for the second gene (R/r): \( R \) (top) and \( r \) (side) → \( Rr \). So the genotype is \( ppRr \).

Step2: Determine the phenotype of X

Now, we use the given allele - phenotype relationships:

- \( P \) = puffy lips, \( p \) = thin lips. Since the genotype for the first gene is \( pp \), the phenotype for lip puffiness/thinness is thin lips (because \( p \) is recessive and we have two \( p \) alleles).

- \( R \) = red lips, \( r \) = purple lips. The genotype for the second gene is \( Rr \). Since \( R \) is dominant over \( r \), the phenotype for lip color is red lips (because we have at least one \( R \) allele).

Answer:

A. ppRr; thin and red lips