Which statement about a heterozygous individual is correct?
A) is pure-breeding
B) has two identical alleles
C) has a dominant allele and a recessive allele
D) expresses the recessive allele in its phenotype
▶️ Answer/Explanation
Ans: C
A heterozygous individual has two different alleles for a gene (e.g., Rr), where R is dominant and r is recessive. The dominant allele masks the recessive one in the phenotype, so only the dominant trait is expressed.
Option A is incorrect (pure-breeding requires homozygous alleles). Option B describes a homozygous individual, and Option D is false (recessive alleles are hidden in heterozygotes). Thus, C is correct.
The seed shape of peas can be smooth or wrinkled. The allele for smooth is dominant and the allele for wrinkled is recessive. Two heterozygous plants are crossed. What is the expected percentage of offspring with a smooth shape?
A) 0%
B) 50%
C) 75%
D) 100%
▶️ Answer/Explanation
Ans: C
To solve this monohybrid cross:
- Let S = smooth (dominant) and s = wrinkled (recessive).
- Heterozygous parents both have genotype Ss.
- A Punnett square shows possible offspring:
- SS (25%) – smooth
- Ss (50%) – smooth
- ss (25%) – wrinkled
Total smooth offspring = 25% (SS) + 50% (Ss) = 75%.
