Are long ears in mice inherited as a dominant trait? - briefly
Yes, the long‑ear phenotype in mice is typically caused by a single dominant allele, so heterozygous individuals express the trait. This inheritance pattern has been confirmed in several laboratory strains carrying the long‑ear mutation.
Are long ears in mice inherited as a dominant trait? - in detail
Elongated ears in laboratory mice are often examined through controlled breeding to determine the mode of inheritance. Classical Mendelian crosses between a normal‑eared strain and a long‑eared strain reveal a 3:1 ratio of offspring with the trait present when the long‑eared parent is homozygous, indicating a single‑gene dominant effect. When heterozygous carriers are crossed with normal individuals, approximately half of the progeny display the phenotype, further supporting dominance.
Molecular studies have identified mutations in the Fgf9 and Shh signaling pathways that increase cartilage growth in the auricular region. These mutations are typically gain‑of‑function alleles; a single copy is sufficient to produce the extended ear structure, while loss‑of‑function alleles result in normal ear size. Knock‑out experiments confirm that removing the mutant allele restores the standard ear length, reinforcing the dominant nature of the mutation.
Key observations from breeding experiments:
- Cross of homozygous long‑eared mice (LL) with normal‑eared mice (ll) yields 100 % long‑eared offspring (Ll).
- Cross of heterozygous long‑eared mice (Ll) with normal‑eared mice (ll) yields roughly 50 % long‑eared and 50 % normal‑eared offspring.
- Cross of two heterozygotes (Ll × Ll) produces a phenotypic ratio close to 3 long‑eared : 1 normal‑eared.
These ratios match expectations for a trait governed by a single dominant allele. Environmental factors, such as diet or housing conditions, do not significantly alter ear length, indicating that the genetic component is the primary determinant.
In summary, experimental breeding data and molecular analyses converge on the conclusion that the elongated ear phenotype in mice is inherited as a dominant trait, driven by specific gain‑of‑function mutations that affect auricular cartilage development.