Question

1. round seeds are dominant over wrinkled seeds in pea plants. fill in the punnett square and determine the expected genotypic and phenotypic ratios from crossing homozygous recessive and heterozygous parents.

genotypes: ________________________ genotypic ratio: ______
phenotypes: ______________________ phenotypic ratio: ______

Explanation:

Step1: Identify Parent Genotypes

Homozygous recessive parent: \( rr \) (since wrinkled is recessive, genotype is \( rr \)). Heterozygous parent: \( Rr \) (round is dominant, heterozygous has one dominant \( R \) and one recessive \( r \)). Wait, but the Punnett square in the image has one parent with \( R, R \) (maybe a typo, but let's use the given Punnett square. The top row is \( R, R \) (heterozygous? Wait, no—wait, the problem says homozygous recessive (\( rr \)) and heterozygous (\( Rr \)). But the Punnett square drawn has left column \( R, r \) and top row \( R, R \). Wait, maybe the parent genotypes are: one parent is \( Rr \) (heterozygous, so gametes \( R \) and \( r \)) and the other is \( rr \)? No, the Punnett square in the image: left column (gametes from one parent) are \( R \) and \( r \), top row (gametes from the other parent) are \( R \) and \( R \). Wait, maybe the parents are: one is \( RR \) (homozygous dominant) and the other is \( Rr \) (heterozygous)? No, the problem says homozygous recessive (\( rr \)) and heterozygous (\( Rr \)). There's a discrepancy, but let's go with the Punnett square given. The Punnett square cells: top-left \( RR \), top-right \( RR \), bottom-left \( Rr \), bottom-right \( Rr \). So gametes from one parent: \( R, R \) (so genotype \( RR \)? No, \( RR \) would produce only \( R \) gametes. Wait, maybe the parent with gametes \( R, r \) is \( Rr \) (heterozygous) and the other parent with gametes \( R, R \) is \( RR \) (homozygous dominant). But the problem says homozygous recessive (\( rr \)) and heterozygous (\( Rr \)). Maybe a typo in the problem or the Punnett square. Let's proceed with the given Punnett square.

Step2: Determine Genotypes from Punnett Square

The Punnett square has four cells: \( RR, RR, Rr, Rr \). So the genotypes present are \( RR \) and \( Rr \). Count the number of each: \( RR \) appears 2 times, \( Rr \) appears 2 times. So genotypic ratio: \( RR : Rr = 2:2 = 1:1 \) (simplified).

Step3: Determine Phenotypes

Since \( R \) (round) is dominant over \( r \) (wrinkled), both \( RR \) and \( Rr \) genotypes will have the round seed phenotype (because even one \( R \) is enough for round). So all four offspring (from the Punnett square) have round seeds. Wait, but the Punnett square has four cells, all with \( RR \) or \( Rr \), so phenotypes are all round. Wait, but the problem says homozygous recessive (\( rr \)) and heterozygous (\( Rr \))—if that's the case, the Punnett square should be:

Parent 1 (homozygous recessive, \( rr \)): gametes \( r, r \)

Parent 2 (heterozygous, \( Rr \)): gametes \( R, r \)

Punnett square:

| | R | r |
|---|---|---|
| r | Rr | rr |
| r | Rr | rr |

Then genotypes: \( Rr, rr, Rr, rr \) (ratio \( Rr:rr = 2:2 = 1:1 \)), phenotypes: round (\( Rr \)) and wrinkled (\( rr \)), ratio \( 1:1 \). But the given Punnett square in the image is different (top row \( R, R \), left column \( R, r \)), so maybe the problem's parent description is wrong, or the Punnett square is for a different cross. Let's use the given Punnett square:

Cells: \( RR, RR, Rr, Rr \)

Genotypes: \( RR \) and \( Rr \). Number of \( RR \): 2, \( Rr \): 2. So genotypic ratio \( RR:Rr = 2:2 = 1:1 \).

Phenotypes: Both \( RR \) and \( Rr \) are round (since \( R \) is dominant), so all four are round. Wait, but 2 \( RR \) and 2 \( Rr \), all round. So phenotypic ratio: round : wrinkled = 4:0? No, wait, the Punnett square has four cells, all with \( RR \) or \( Rr \), so all are round. But that would be if one parent is \( RR \) (homozygous dominant) and the other is \( Rr \) (heterozygous). Let's check:

Parent 1: \( RR \) (gametes \( R, R \))

Parent 2: \( Rr \) (gametes \( R, r \))

Punnett square:

| | R | R |
|---|---|---|
| R | RR | RR |
| r | Rr | Rr |

Yes, that's the given Punnett square. So the problem's description might have a typo (saying homozygous recessive instead of homozygous dominant). Let's proceed with the given Punnett square.

Step4: Genotypic Ratio

Count the genotypes: \( RR \) (2 cells), \( Rr \) (2 cells). So ratio \( RR : Rr = 2:2 = 1:1 \).

Step5: Phenotypic Ratio

Both \( RR \) and \( Rr \) show the dominant phenotype (round seeds), so all 4 offspring are round. Wait, 2 \( RR \) and 2 \( Rr \), so total round: 4, wrinkled: 0? But that seems odd. Wait, no—wait, the Punnett square has four cells: top-left \( RR \), top-right \( RR \), bottom-left \( Rr \), bottom-right \( Rr \). So four offspring: two \( RR \), two \( Rr \). All have round seeds (since \( R \) is dominant). So phenotypic ratio: round : wrinkled = 4:0? But that's not typical. Alternatively, maybe the parent with left column \( R, r \) is \( Rr \) (heterozygous) and the top row \( R, R \) is \( RR \) (homozygous dominant). Then the cross is \( RR \times Rr \).

Genotypes: \( RR \) (from \( R \times R \)) and \( Rr \) (from \( R \times r \)). Number of \( RR \): 2 (top row: \( R \times R \) twice), number of \( Rr \): 2 (bottom row: \( R \times r \) twice). So genotypic ratio \( RR:Rr = 2:2 = 1:1 \).

Phenotypes: All \( RR \) and \( Rr \) are round, so phenotypic ratio: round : wrinkled = 4:0? But that's not a typical ratio. Wait, maybe the problem meant homozygous dominant (\( RR \)) and heterozygous (\( Rr \)) instead of homozygous recessive. Let's go with the given Punnett square.

So:

Genotypes: \( RR \) and \( Rr \)

Genotypic Ratio: \( RR : Rr = 2:2 = 1:1 \) (or simplified \( 1:1 \))

Phenotypes: Round (since both \( RR \) and \( Rr \) have the dominant allele \( R \))

Phenotypic Ratio: Round : Wrinkled = 4:0? No, wait, 2 \( RR \) and 2 \( Rr \), all round, so 4 round, 0 wrinkled. But that's unusual. Alternatively, maybe the Punnett square was drawn incorrectly. Let's re-express:

If the parents are \( Rr \) (heterozygous, gametes \( R, r \)) and \( rr \) (homozygous recessive, gametes \( r, r \)):

Punnett square:

| | R | r |
|---|---|---|
| r | Rr | rr |
| r | Rr | rr |

Then genotypes: \( Rr \) (2), \( rr \) (2) → ratio \( 1:1 \)

Phenotypes: Round (\( Rr \)) and Wrinkled (\( rr \)) → ratio \( 1:1 \)

But the given Punnett square doesn't match this. The given Punnett square has top row \( R, R \) and left column \( R, r \), so let's stick to that.

So:

Genotypes: \( RR \), \( Rr \)

Genotypic Ratio: \( RR : Rr = 2:2 = 1:1 \)

Phenotypes: Round (all, since \( R \) is dominant)

Phenotypic Ratio: Round : Wrinkled = 4:0 (or 1:0, but that's not useful). Wait, maybe the problem's Punnett square has a typo, and the left column is \( r, r \) (homozygous recessive) and top row \( R, r \) (heterozygous). Let's assume that correction.

Parent 1: \( rr \) (gametes \( r, r \))

Parent 2: \( Rr \) (gametes \( R, r \))

Punnett square:

| | R | r |
|---|---|---|
| r | Rr | rr |
| r | Rr | rr |

Then:

Genotypes: \( Rr \) (2), \( rr \) (2) → Genotypic Ratio: \( Rr : rr = 2:2 = 1:1 \)

Phenotypes: Round (\( Rr \)) and Wrinkled (\( rr \)) → Phenotypic Ratio: \( 2:2 = 1:1 \)

This makes more sense with the problem statement (homozygous recessive \( rr \) and heterozygous \( Rr \)). So likely the Punnett square in the image has a typo (left column \( R, r \) should be \( r, r \)). Let's proceed with this correct cross.

Step1 (Correct Cross): Identify Parent Genotypes

Homozygous recessive: \( rr \) (gametes: \( r, r \))

Heterozygous: \( Rr \) (gametes: \( R, r \))

Step2: Fill Punnett Square

| | \( R \) | \( r \) |
|-------|---------|---------|
| \( r \) | \( Rr \) | \( rr \) |
| \( r \) | \( Rr \) | \( rr \) |

Step3: Determine Genotypes

Genotypes present: \( Rr \) (2 cells) and \( rr \) (2 cells)

Step4: Genotypic Ratio

Count: \( Rr \): 2, \( rr \): 2 → Ratio: \( Rr : rr = 2:2 = 1:1 \)

Step5: Determine Phenotypes

- \( Rr \): Round (dominant allele \( R \) present)
- \( rr \): Wrinkled (recessive allele only)

Step6: Phenotypic Ratio

Round (\( Rr \)): 2, Wrinkled (\( rr \)): 2 → Ratio: \( 2:2 = 1:1 \)

Answer:

Genotypes: \( Rr, rr \)
Genotypic Ratio: \( Rr : rr = 1:1 \)
Phenotypes: Round, Wrinkled
Phenotypic Ratio: \( \text{Round} : \text{Wrinkled} = 1:1 \)

(Note: The given Punnett square in the image likely has a typo; the correct cross for homozygous recessive (\( rr \)) and heterozygous (\( Rr \)) produces this result.)