Recessive allele

Definition

A recessive allele is a variant of a gene that must be present in two copies (homozygous) for its trait to be expressed in an organism. In cases where a dominant allele is also present, the dominant allele will mask the expression of the recessive one, demonstrating how certain traits can be inherited without being visibly expressed. This concept is crucial for understanding genetic inheritance patterns and how traits are passed down through generations.

5 Must Know Facts For Your Next Test

1. Recessive alleles can only influence an organism's phenotype when an individual inherits two copies of that allele, one from each parent.
2. In incomplete dominance, the presence of a recessive allele can result in a blended phenotype, as seen in certain flower colors where neither allele completely dominates.
3. In codominance, both alleles are expressed equally in the phenotype, but a recessive allele will still not show its trait if paired with a dominant allele.
4. Mendel's experiments with pea plants revealed the principles of segregation and independent assortment, which help explain how recessive alleles are inherited across generations.
5. Punnett squares are often used to predict the genotypic and phenotypic ratios of offspring based on the combination of dominant and recessive alleles in parental genotypes.

Review Questions

• How does the presence of a recessive allele impact the phenotypic expression of traits in offspring?
  • The presence of a recessive allele impacts phenotypic expression by requiring two copies for the trait to be visible. If an organism has one dominant and one recessive allele, only the dominant trait will be expressed in its phenotype. This means that traits governed by recessive alleles can remain hidden in heterozygous individuals but can reappear in subsequent generations if two carriers mate.
• Discuss the role of Mendel's laws in understanding how recessive alleles are inherited during monohybrid and dihybrid crosses.
  • Mendel's laws, particularly the law of segregation, explain how recessive alleles are inherited. During a monohybrid cross, each parent contributes one allele to the offspring, resulting in a 3:1 phenotypic ratio for dominant to recessive traits when both parents are heterozygous. In dihybrid crosses, Mendel’s law of independent assortment shows that alleles for different genes segregate independently, allowing for various combinations of dominant and recessive alleles, demonstrating more complex inheritance patterns.
• Evaluate how understanding recessive alleles contributes to advancements in genetics and potential applications in medicine and agriculture.
  • Understanding recessive alleles significantly contributes to genetics by aiding in predicting inheritance patterns and diagnosing genetic disorders. In medicine, identifying carriers of diseases linked to recessive alleles allows for better family planning and screening strategies. In agriculture, selective breeding can harness desirable traits linked to recessive alleles, leading to improved crop varieties. This knowledge ultimately enhances our ability to manipulate genetic outcomes for health and food security.

Related terms

dominant allele: A dominant allele is a variant of a gene that expresses its trait even in the presence of a different allele. It can mask the expression of a recessive allele in a heterozygous condition.

homozygous: Homozygous refers to having two identical alleles for a particular gene, which can be either both dominant or both recessive.

phenotype: Phenotype is the observable physical and physiological traits of an organism, which result from the interaction of its genotype with the environment.