What would be the result if mice have a dominant trait of long ears and a recessive trait of short ears, and a male is crossed? - briefly
If the male contributes a dominant allele for ear length, every offspring will exhibit long ears; short‑eared progeny arise only when both parents are homozygous recessive.
What would be the result if mice have a dominant trait of long ears and a recessive trait of short ears, and a male is crossed? - in detail
Mice possess two alleles for ear length: L (dominant, long ears) and l (recessive, short ears). When a male is mated, the genetic composition of the sire determines the distribution of offspring phenotypes.
Male homozygous dominant (LL) × female recessive (ll)
Male heterozygous (Ll) × female recessive (ll)
- Gametes: male L or l (½ each), female l.
- Offspring genotypes: ½ Ll, ½ ll.
- Phenotype ratio: 1 long‑eared : 1 short‑eared (50 % each).
Male homozygous dominant (LL) × female heterozygous (Ll)
- Gametes: male L, female L or l (½ each).
- Offspring genotypes: ½ LL, ½ Ll.
- Phenotype: 100 % long‑eared, but ¼ of the population is homozygous dominant.
Male heterozygous (Ll) × female heterozygous (Ll)
- Gametes: each parent produces L and l equally.
- Punnett square yields: ¼ LL, ½ Ll, ¼ ll.
- Phenotype ratio: 3 long‑eared : 1 short‑eared (75 % vs. 25 %).
If the female genotype is unknown, the expected phenotype distribution depends on the male’s genotype and the population frequency of the recessive allele. Assuming random mating with a low frequency of l, most crosses will produce predominantly long‑eared offspring, with short‑eared individuals appearing only when both parents contribute the recessive allele.