Are long ears in mice inherited as a dominant trait and short ears as a recessive trait? - briefly
The allele for elongated ears is dominant, so heterozygous mice exhibit the long‑ear phenotype, while the allele for reduced ear length is recessive and expresses only in homozygotes. Crosses between long‑ear and short‑ear strains consistently produce progeny with long ears, confirming this inheritance pattern.
Are long ears in mice inherited as a dominant trait and short ears as a recessive trait? - in detail
The ear‑length phenotype in laboratory mice follows a classic Mendelian pattern in many strains. A single gene, often designated El (for elongated ear), carries two alleles: a dominant allele that produces long ears and a recessive allele that results in short ears. When a mouse possesses at least one copy of the dominant allele (genotype El/El or El/el), the long‑ear phenotype is expressed. Mice homozygous for the recessive allele (el/el) display short ears.
Breeding experiments illustrate the expected ratios. Crossing two heterozygous individuals (El/el × El/el) yields offspring in the proportion 3 long‑ear : 1 short‑ear. The genotype distribution is 1 El/El, 2 El/el, and 1 el/el. A cross between a homozygous dominant (El/El) and a homozygous recessive (el/el) produces 100 % long‑ear progeny, confirming the dominance of the elongated‑ear allele.
Phenotypic expression can be modified by incomplete penetrance or variable expressivity, but in the majority of inbred lines the trait remains fully penetrant. Molecular analyses have identified the El locus on chromosome X, with the dominant allele encoding a gain‑of‑function mutation in a regulatory gene that enhances cartilage growth in the auricular region. The recessive allele represents the wild‑type sequence lacking this activation.
Environmental factors, such as nutrition or temperature, affect overall ear development but do not alter the underlying inheritance pattern. Studies involving cross‑species hybrids show that the dominant allele retains its effect, indicating a conserved mechanism across murine species.
In summary:
- A single gene determines ear length, with a dominant allele for long ears and a recessive allele for short ears.
- Heterozygous carriers exhibit the long‑ear phenotype.
- Expected offspring ratios from Mendelian crosses match observed data in controlled breeding programs.
- Molecular identification of the El locus confirms the genetic basis of the trait.
- Minor phenotypic variation may arise from penetrance, expressivity, or environmental influences, without changing the fundamental dominance relationship.