How do alleles differ from each other at the molecular level?
How do alleles differ from each other at the molecular level?
Answer
Alleles are variant forms of a gene that differ in their nucleotide sequences at a specific locus on a chromosome. This molecular variation is crucial for genetic diversity and can influence phenotypic traits, such as eye color or disease susceptibility.
Molecular Differences Between Alleles
Nucleotide Sequence Variation
At the molecular level, alleles differ primarily in their nucleotide sequences. For instance, a gene may have multiple alleles that vary by one or more bases. This can occur through mutations such as substitutions, deletions, or insertions of nucleotides. These variations can lead to different amino acid sequences in proteins, which may affect the protein’s function and, consequently, the organism’s phenotype.
Types of Mutations
- Point Mutations: A change in a single nucleotide base (e.g., adenine to guanine) can create an allele that produces a different protein product or alters gene expression.
- Insertions and Deletions: Adding or removing nucleotides can shift the reading frame of the gene, potentially leading to significant functional changes in the resultant protein.
- Structural Variations: Larger-scale mutations can involve duplications or deletions of entire gene segments, affecting multiple alleles simultaneously.
Functional Implications
The differences in nucleotide sequences among alleles can result in varying levels of gene expression or different protein functionalities. For example:
- Dominant vs. Recessive Alleles: Some alleles may be dominant, meaning their effects are expressed in the phenotype even when only one copy is present (e.g., brown eyes dominate over blue). Recessive alleles require two copies to manifest their traits.
- Codominance: In some cases, both alleles can be expressed equally, as seen in the ABO blood group system where individuals can express both A and B antigens if they inherit one allele for each.
Genetic Diversity and Evolution
Allelic variation is fundamental to genetic diversity within populations. It provides raw material for natural selection and evolution, enabling species to adapt to changing environments. The accumulation of these variations over generations contributes to the evolutionary process
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