Question

1. complete the punnett square problems using \b\ for black and \b\ for white. give genotypes and phenotypes.

• a heterozygous individual is crossed with a homozygous recessive plant.
• a homozygous dominant plant is crossed with a hybrid.

Explanation:

First Sub - Problem: Heterozygous × Homozygous Recessive

Step1: Identify Genotypes

Heterozygous: \( Bb \) (since it has one dominant and one recessive allele). Homozygous recessive: \( bb \) (two recessive alleles).

Step2: Set Up Punnett Square

The gametes from \( Bb \) are \( B \) and \( b \). The gametes from \( bb \) are \( b \) and \( b \).

	\( B \)	\( b \)
\( b \)	\( Bb \)	\( bb \)

Step3: Determine Genotypes

From the Punnett Square, the genotypes are \( Bb \) (2 out of 4) and \( bb \) (2 out of 4). So the genotypic ratio is \( 1:1 \) (\( Bb:bb \)).

Step4: Determine Phenotypes

• \( Bb \): Since \( B \) is dominant (black), the phenotype is black.
• \( bb \): Since \( b \) is recessive (white), the phenotype is white.

The phenotypic ratio is \( 1:1 \) (black: white).

Second Sub - Problem: Homozygous Dominant × Hybrid

Step1: Identify Genotypes

Homozygous dominant: \( BB \) (two dominant alleles). Hybrid (heterozygous): \( Bb \) (one dominant and one recessive allele).

Step2: Set Up Punnett Square

The gametes from \( BB \) are \( B \) and \( B \). The gametes from \( Bb \) are \( B \) and \( b \).

	\( B \)	\( B \)
\( b \)	\( Bb \)	\( Bb \)

Step3: Determine Genotypes

From the Punnett Square, the genotypes are \( BB \) (2 out of 4) and \( Bb \) (2 out of 4). The genotypic ratio is \( 1:1 \) (\( BB:Bb \)).

Step4: Determine Phenotypes

• \( BB \): Phenotype is black (since \( B \) is dominant).
• \( Bb \): Phenotype is black (since \( B \) is dominant).

The phenotypic ratio is \( 4:0 \) (all black) or we can say the phenotype of all offspring is black.

Answer:

s:

First Cross (Heterozygous × Homozygous Recessive)

• Genotypes: \( Bb \) (50%), \( bb \) (50%) or ratio \( 1:1 \) (\( Bb:bb \))
• Phenotypes: Black (50%), White (50%) or ratio \( 1:1 \) (black: white)

Second Cross (Homozygous Dominant × Hybrid)

• Genotypes: \( BB \) (50%), \( Bb \) (50%) or ratio \( 1:1 \) (\( BB:Bb \))
• Phenotypes: All black (100% black)