Allele

Definition

An allele is a variant form of a gene that is located at a specific position on a chromosome. Different alleles can result in variations in traits, such as eye color or blood type, and contribute to the genetic diversity within a population. Alleles can be dominant or recessive, influencing how traits are expressed in an organism.

5 Must Know Facts For Your Next Test

1. Alleles can exist in multiple forms, leading to variations in traits among individuals within a species.
2. Dominant alleles mask the effects of recessive alleles when both are present in a genotype.
3. Homozygous individuals have two identical alleles for a trait, while heterozygous individuals have two different alleles.
4. Alleles can arise through mutations in DNA, contributing to genetic diversity and evolution.
5. In diploid organisms, each individual inherits one allele from each parent for every gene.

Review Questions

• How do dominant and recessive alleles affect the expression of traits in an organism?
  • Dominant alleles can mask the effects of recessive alleles when both are present in the genotype. This means that if an individual has at least one dominant allele for a trait, that trait will be expressed phenotypically. For example, if 'A' is a dominant allele for brown eyes and 'a' is a recessive allele for blue eyes, individuals with genotypes 'AA' and 'Aa' will have brown eyes, while only individuals with the genotype 'aa' will exhibit blue eyes.
• In what ways do alleles contribute to genetic diversity within populations?
  • Alleles contribute to genetic diversity through variations in traits that arise from different allele combinations among individuals. These variations can result from mutations that create new alleles or through sexual reproduction that shuffles existing alleles. As populations adapt to changing environments or face selective pressures, diverse alleles play a critical role in natural selection, allowing for variations that enhance survival and reproduction rates among individuals.
• Evaluate the importance of understanding alleles in the context of genetic diseases and inheritance patterns.
  • Understanding alleles is crucial for studying genetic diseases and inheritance patterns because many conditions are linked to specific alleles. For instance, knowing whether a disease-causing allele is dominant or recessive helps predict how it may be inherited within families. By analyzing genotypes and identifying carrier statuses, genetic counseling can inform individuals about their risks of passing on certain traits or diseases to their offspring. This knowledge plays a vital role in making informed reproductive choices and developing targeted treatments.

Related terms

gene: A segment of DNA that contains the instructions for producing a specific protein or functional RNA molecule.

genotype: The genetic makeup of an individual, including the alleles present at specific loci on their chromosomes.

phenotype: The observable physical or biochemical characteristics of an organism, determined by both its genotype and environmental factors.