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Sagot :
Certainly! Let's break down the problem to understand the inheritance of the two traits: earlobe attachment and the presence of a cleft chin.
### Genetic Notation
- Unattached earlobes (U) are dominant over attached earlobes (u).
- Cleft chin (C) is dominant over no cleft chin (c).
### Parental Genotypes
Both parents are heterozygous for both traits, meaning their genotypes are:
- Parent 1: UuCc
- Parent 2: UuCc
### Punnett Square Analysis
To determine the offspring genotypes, we need to create a Punnett square, where we consider all possible combinations of the alleles from each parent.
Here are the combinations of alleles each parent can contribute:
- Parent 1 can produce four possible gametes: UC, Uc, uC, and uc.
- Parent 2 can also produce the same four possibilities: UC, Uc, uC, and uc.
By using a Punnett square, we calculate each possible combination of these alleles:
| | UC | Uc | uC | uc |
|-------|-------|-------|-------|-------|
| UC| UUCC | UUCc | UuCC | UuCc |
| Uc| UUCc | UUcc | UuCc | Uucc |
| uC| UuCC | UuCc | uuCC | uuCc |
| uc| UuCc | Uucc | uuCc | uucc |
### Phenotype Ratios
From the Punnett square, we can determine how frequently each phenotype appears:
1. Unattached earlobes and cleft chin (U-C-):
This phenotype has any combination of at least one dominant allele for both traits:
- UUCC, UUCc, UuCC, UuCc
Counting these:
- 9 combinations out of 16 result in unattached earlobes and a cleft chin.
2. Unattached earlobes and no cleft chin (U-cc):
This phenotype requires at least one dominant allele for unattached earlobes and two recessive alleles for no cleft chin:
- UUcc, Uucc
Counting these:
- 3 combinations out of 16 result in unattached earlobes and no cleft chin.
3. Attached earlobes and cleft chin (uuC-):
This phenotype requires two recessive alleles for attached earlobes and at least one dominant allele for cleft chin:
- uuCC, uuCc
Counting these:
- 3 combinations out of 16 result in attached earlobes and a cleft chin.
4. Attached earlobes and no cleft chin (uucc):
This phenotype requires two recessive alleles for both traits:
- uucc
Counting these:
- 1 combination out of 16 results in attached earlobes and no cleft chin.
### Final Ratios
Summarizing the phenotype ratios:
- Unattached earlobes and cleft chin: 9 out of 16
- Unattached earlobes and no cleft chin: 3 out of 16
- Attached earlobes and cleft chin: 3 out of 16
- Attached earlobes and no cleft chin: 1 out of 16
So the final phenotype ratio is:
[tex]\[ 9 : 3 : 3 : 1 \][/tex]
### Genetic Notation
- Unattached earlobes (U) are dominant over attached earlobes (u).
- Cleft chin (C) is dominant over no cleft chin (c).
### Parental Genotypes
Both parents are heterozygous for both traits, meaning their genotypes are:
- Parent 1: UuCc
- Parent 2: UuCc
### Punnett Square Analysis
To determine the offspring genotypes, we need to create a Punnett square, where we consider all possible combinations of the alleles from each parent.
Here are the combinations of alleles each parent can contribute:
- Parent 1 can produce four possible gametes: UC, Uc, uC, and uc.
- Parent 2 can also produce the same four possibilities: UC, Uc, uC, and uc.
By using a Punnett square, we calculate each possible combination of these alleles:
| | UC | Uc | uC | uc |
|-------|-------|-------|-------|-------|
| UC| UUCC | UUCc | UuCC | UuCc |
| Uc| UUCc | UUcc | UuCc | Uucc |
| uC| UuCC | UuCc | uuCC | uuCc |
| uc| UuCc | Uucc | uuCc | uucc |
### Phenotype Ratios
From the Punnett square, we can determine how frequently each phenotype appears:
1. Unattached earlobes and cleft chin (U-C-):
This phenotype has any combination of at least one dominant allele for both traits:
- UUCC, UUCc, UuCC, UuCc
Counting these:
- 9 combinations out of 16 result in unattached earlobes and a cleft chin.
2. Unattached earlobes and no cleft chin (U-cc):
This phenotype requires at least one dominant allele for unattached earlobes and two recessive alleles for no cleft chin:
- UUcc, Uucc
Counting these:
- 3 combinations out of 16 result in unattached earlobes and no cleft chin.
3. Attached earlobes and cleft chin (uuC-):
This phenotype requires two recessive alleles for attached earlobes and at least one dominant allele for cleft chin:
- uuCC, uuCc
Counting these:
- 3 combinations out of 16 result in attached earlobes and a cleft chin.
4. Attached earlobes and no cleft chin (uucc):
This phenotype requires two recessive alleles for both traits:
- uucc
Counting these:
- 1 combination out of 16 results in attached earlobes and no cleft chin.
### Final Ratios
Summarizing the phenotype ratios:
- Unattached earlobes and cleft chin: 9 out of 16
- Unattached earlobes and no cleft chin: 3 out of 16
- Attached earlobes and cleft chin: 3 out of 16
- Attached earlobes and no cleft chin: 1 out of 16
So the final phenotype ratio is:
[tex]\[ 9 : 3 : 3 : 1 \][/tex]
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