How are long ears inherited in mice? - briefly
Long ear length in mice is usually governed by an autosomal recessive allele, requiring homozygosity for the phenotype to appear. Breeding two heterozygous carriers produces a 25 % probability of offspring displaying the trait.
How are long ears inherited in mice? - in detail
The elongated pinna trait in laboratory mice results from a mutation at a single autosomal locus, commonly designated le. The allele behaves as a semi‑dominant factor: heterozygous individuals display markedly longer ears than wild‑type, while homozygous carriers often exhibit severe craniofacial abnormalities and reduced viability.
Mendelian segregation in a cross between a normal mouse (le⁺/le⁺) and a heterozygote (le⁺/le) yields a 1 : 1 ratio of normal to long‑ear offspring in the F₁ generation. Interbreeding F₁ heterozygotes produces an F₂ distribution of approximately 1 : 2 : 1 (normal : heterozygous long‑ear : homozygous affected), confirming autosomal inheritance with incomplete dominance.
Genetic mapping places the le mutation on chromosome 1, near the locus that controls cartilage growth. Molecular analyses have identified a missense change in the Fgfr2 gene that alters receptor signaling, leading to prolonged chondrocyte proliferation in the auricular cartilage.
Environmental modifiers influence phenotypic expression. Nutritional status and temperature affect cartilage development, producing variability in ear length among genetically identical individuals.
Key characteristics of the inheritance pattern:
- Autosomal location, not linked to sex chromosomes.
- Semi‑dominant expression: heterozygotes show the phenotype; homozygotes experience additional defects.
- Approximate phenotypic ratios in controlled crosses: 1 : 2 : 1 (normal : heterozygous : homozygous).
- Molecular basis: point mutation in a growth‑factor receptor gene affecting cartilage growth.
- Modifier factors: diet, ambient temperature, and epistatic interactions with other loci.
Understanding this mechanism informs breeding strategies for experimental colonies and provides a model for studying cartilage development and related genetic disorders.