In testing qualitative traits with complete dominance, one option is to mate the sire with a dam that is known to be a carrier. Is this statement listed as a testing approach?

In testing qualitative traits with complete dominance, one option is to mate the sire with a dam that is known to be a carrier. Is this statement listed as a testing approach?

• A. Mate sire with dams that are known carriers
• B. Mate sire to a dam that is homozygous recessive
• C. Mate sire to his daughter
• D. Mate to a random population

Answer: (A)

Testing matings with a known carrier dam is a classic way to reveal whether a sire carries the recessive allele when the trait shows complete dominance. In a dominant phenotype, you can’t tell if an individual is AA or Aa just by appearance. By crossing the sire with a dam that is known to be Aa, you create a situation where the recessive allele from the dam can be paired with the sire’s alleles. If the sire is AA, all offspring will show the dominant phenotype (AA or Aa). If the sire is Aa, there will be some offspring with the recessive phenotype (aa) because the dam can supply a recessive allele and the sire can contribute either an A or a carry of a, leading to aa in the next generation. Observing any recessive offspring confirms the sire carries the recessive allele; not observing recessive offspring (in a large enough sample) suggests the sire is homozygous dominant. This makes it a practical, informative testing approach for genotype determination in qualitative traits with complete dominance.

Testing matings with a known carrier dam is a classic way to reveal whether a sire carries the recessive allele when the trait shows complete dominance. In a dominant phenotype, you can’t tell if an individual is AA or Aa just by appearance. By crossing the sire with a dam that is known to be Aa, you create a situation where the recessive allele from the dam can be paired with the sire’s alleles. If the sire is AA, all offspring will show the dominant phenotype (AA or Aa). If the sire is Aa, there will be some offspring with the recessive phenotype (aa) because the dam can supply a recessive allele and the sire can contribute either an A or a carry of a, leading to aa in the next generation. Observing any recessive offspring confirms the sire carries the recessive allele; not observing recessive offspring (in a large enough sample) suggests the sire is homozygous dominant. This makes it a practical, informative testing approach for genotype determination in qualitative traits with complete dominance.