Certainly! Let's determine the ratio of offspring with each described trait to the total number of offspring when parents heterozygous for both traits are crossed.
### Genetic Background:
1. Unattached earlobes (E) are dominant to attached earlobes (e).
2. Cleft chin (A) is dominant to no cleft chin (a).
3. Both parents are heterozygous for both traits (genotype EeAa).
### Determining Genotypes:
When we cross two heterozygous parents (EeAa), we need to set up a Punnett square to consider all possible combinations of alleles for the offspring.
### Punnett Square:
Below is the 4x4 Punnett square for the cross of EeAa x EeAa:
| | EA | Ea | eA | ea |
|----------|----------|---------|---------|---------|
| EA | EEAA | EEAa | EeAA | EeAa |
| Ea | EEAa | EEaa | EeAa | Eeaa |
| eA | EeAA | EeAa | eeAA | eeAa |
| ea | EeAa | Eeaa | eeAa | eeaa |
### Phenotypes and Corresponding Genotypes:
1. Unattached earlobes and cleft chin (E_A_):
- Genotypes: EEAA, EEAa, EeAA, EeAa
2. Unattached earlobes and no cleft chin (E_aa):
- Genotypes: EEaa, Eeaa
3. Attached earlobes and cleft chin (eeA_):
- Genotypes: eeAA, eeAa
4. Attached earlobes and no cleft chin (eeaa):
- Genotype: eeaa
### Counting the Genotypes:
From the Punnett square, we can count the number of occurrences of each genotype that corresponds to the phenotypes mentioned:
1. Unattached earlobes and cleft chin (EEAA, EEAa, EeAA, EeAa)
- Count: 9
2. Unattached earlobes and no cleft chin (EEaa, Eeaa)
- Count: 3
3. Attached earlobes and cleft chin (eeAA, eeAa)
- Count: 3
4. Attached earlobes and no cleft chin (eeaa)
- Count: 1
### Ratios:
Thus, the ratio of offspring with each described phenotype to the total number of offspring is:
1. Unattached earlobes and cleft chin: 9
2. Unattached earlobes and no cleft chin: 3
3. Attached earlobes and cleft chin: 3
4. Attached earlobes and no cleft chin: 1
This can also be written in the form 9:3:3:1.
