The two DNA and polypeptide sequences shown are for alleles at a hypothetical locus that produce different polypeptides, both five amino acids long. In each case, the lower DNA strand is the template strand: allele A₁ 5′. . . ATGCATGTAAGTGCATGA. . . 3′ 3′. . . TACGTACATTCACGTACT. . . 5′ A₁ polypeptide N–Met–His–Val–Ser–Ala–C allele A₂ 5′. . . ATGCAAGTAAGTGCATGA . . . 3′ 3′. . . TACGTTCATTCACGTACT . . . 5′ A₂ polypeptide. N–Met–Gln–Val–Ser–Ala–C Based on DNA and polypeptide sequences alone, is there any way to determine which allele is dominant and which is recessive? Why or why not?

Verified step by step guidance

1. Step 1: Understand the concept of dominance and recessiveness in alleles. Dominance refers to an allele that expresses its phenotype even in the presence of a different allele, while recessiveness refers to an allele whose phenotype is masked by a dominant allele.
2. Step 2: Analyze the DNA sequences provided for both alleles A₁ and A₂. Note that the sequences differ at a specific point, which leads to a change in the amino acid sequence of the polypeptides they encode.
3. Step 3: Compare the polypeptide sequences resulting from each allele. Allele A₁ produces a polypeptide with the sequence Met–His–Val–Ser–Ala, while allele A₂ produces Met–Gln–Val–Ser–Ala. The difference is in the second amino acid: His in A₁ and Gln in A₂.
4. Step 4: Consider the information provided. The problem does not give any phenotypic information or context about the functional consequences of these polypeptides, which is crucial for determining dominance.
5. Step 5: Conclude that without additional phenotypic data or functional analysis, it is not possible to determine which allele is dominant or recessive based solely on the DNA and polypeptide sequences. Dominance is a phenotypic concept, not a genotypic one.

Key Concepts

Alleles and Dominance

Alleles are different versions of a gene that arise by mutation and are found at the same place on a chromosome. Dominance refers to the relationship between alleles, where one allele can mask the expression of another. In genetics, a dominant allele will express its trait even in the presence of a recessive allele, while a recessive allele only expresses its trait when paired with another recessive allele.

Transcription and Translation

Transcription is the process by which the DNA sequence of a gene is copied into messenger RNA (mRNA), which then undergoes translation to synthesize polypeptides (proteins). The sequence of nucleotides in DNA determines the sequence of amino acids in a polypeptide, which ultimately influences the protein's function. Understanding these processes is crucial for analyzing how genetic information is expressed.

Phenotypic Expression

Phenotypic expression refers to the observable traits or characteristics of an organism, which result from the interaction of its genotype (the genetic makeup) with the environment. In the context of alleles, the phenotype can be influenced by whether an allele is dominant or recessive. However, without additional information about the functional effects of the polypeptides produced by the alleles, it is not possible to determine dominance solely from the sequences provided.