If heterozygous cacti are crossed, 25% of offspring are expected to have short arms (aa).
- According to this question, a gene coding for arm length in cacti is involved. The long arm (A) is said to be dominant over short arm (a).
- If two heterozygous cacti are crossed i.e. Aa × Aa, the following gametes will be formed by each heterozygous parent: A and a.
- The fertilization of these two gametes (A and a) will give rise to the following genotype of offsprings: AA, Aa, Aa, and aa (see attached image).
- Genotypes AA, Aa have long arms while genotype aa have short arms. Since 1/4 of offsprings have genotype 'aa', hence, 1/4 × 100 = 25% are expected to have short arms (aa).
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