Question
In a cross between two plants, one parent is heterozygous for two traits (AaBb) and the other parent is homozygous recessive for both traits (aabb). Trait A exhibits incomplete dominance, while trait B exhibits complete dominance.
What is the expected phenotypic ratio of the offspring?
A.
1:1:1:1
B.
1:2:1:2
C.
3:1
D.
9:3:3:1
What is the expected phenotypic ratio of the offspring?
A.
1:1:1:1
B.
1:2:1:2
C.
3:1
D.
9:3:3:1
Answers
GPT-4o mini
To determine the expected phenotypic ratio of the offspring from the cross between the two plants, we can follow these steps:
1. **Identify the genotypes of the parents:**
- Parent 1 (heterozygous for two traits): AaBb
- Parent 2 (homozygous recessive for both traits): aabb
2. **Determine the gametes produced by each parent:**
- Parent 1 (AaBb) can produce the following gametes: AB, Ab, aB, ab
- Parent 2 (aabb) can only produce the following gamete: ab
3. **Set up the Punnett square:**
- The cross would be between the gametes of both parents:
```
ab
----------------
AB | AaBb (trait A: incomplete dominance; trait B: dominant)
Ab | Aabb (trait A: incomplete dominance; trait B: recessive)
aB | aaBb (trait A: recessive; trait B: dominant)
ab | aabb (trait A: recessive; trait B: recessive)
```
4. **Determine the phenotypes:**
- **AaBb**: Trait A (incomplete dominance): expression depends on genotype; dominant phenotype if AA or Aa, but a blended phenotype if heterozygous (A and a lead to an intermediate trait). For B, Bb is dominant, so shows dominant phenotype.
- **Aabb**: Dominant for A and recessive for B (one of the phenotypes from trait A and recessive from trait B).
- **aaBb**: Recessive for A and dominant for B (shows dominant phenotype B and recessive phenotype A).
- **aabb**: Recessive for both traits (shows recessive phenotype for both traits A and B).
5. **Count the phenotypes:**
- We have one of each phenotypic combination:
- 1 AaBb
- 1 Aabb
- 1 aaBb
- 1 aabb
The phenotypic outcomes based on the dominant and recessive traits:
- Trait A: **1 (one with dominant A, two with recessive a), 2 mixed pheno (Aa will have intermediate mix)**
- Trait B: **2 dominant (Bb) and 2 recessive (bb)**
So overall, the phenotypic ratio turns out to be:
- 1 AaBb : 1 Aabb : 1 aaBb : 1 aabb
This leads us to a resulting ratio of **1:1:1:1**.
Thus, the expected phenotypic ratio of the offspring is **A. 1:1:1:1**.
1. **Identify the genotypes of the parents:**
- Parent 1 (heterozygous for two traits): AaBb
- Parent 2 (homozygous recessive for both traits): aabb
2. **Determine the gametes produced by each parent:**
- Parent 1 (AaBb) can produce the following gametes: AB, Ab, aB, ab
- Parent 2 (aabb) can only produce the following gamete: ab
3. **Set up the Punnett square:**
- The cross would be between the gametes of both parents:
```
ab
----------------
AB | AaBb (trait A: incomplete dominance; trait B: dominant)
Ab | Aabb (trait A: incomplete dominance; trait B: recessive)
aB | aaBb (trait A: recessive; trait B: dominant)
ab | aabb (trait A: recessive; trait B: recessive)
```
4. **Determine the phenotypes:**
- **AaBb**: Trait A (incomplete dominance): expression depends on genotype; dominant phenotype if AA or Aa, but a blended phenotype if heterozygous (A and a lead to an intermediate trait). For B, Bb is dominant, so shows dominant phenotype.
- **Aabb**: Dominant for A and recessive for B (one of the phenotypes from trait A and recessive from trait B).
- **aaBb**: Recessive for A and dominant for B (shows dominant phenotype B and recessive phenotype A).
- **aabb**: Recessive for both traits (shows recessive phenotype for both traits A and B).
5. **Count the phenotypes:**
- We have one of each phenotypic combination:
- 1 AaBb
- 1 Aabb
- 1 aaBb
- 1 aabb
The phenotypic outcomes based on the dominant and recessive traits:
- Trait A: **1 (one with dominant A, two with recessive a), 2 mixed pheno (Aa will have intermediate mix)**
- Trait B: **2 dominant (Bb) and 2 recessive (bb)**
So overall, the phenotypic ratio turns out to be:
- 1 AaBb : 1 Aabb : 1 aaBb : 1 aabb
This leads us to a resulting ratio of **1:1:1:1**.
Thus, the expected phenotypic ratio of the offspring is **A. 1:1:1:1**.