Pedigree analysis for earlobe attachment (free dominant, attached recessive)

Steps:

• Identify phenotypes: attached earlobes indicate homozygous recessive (aa); free earlobes indicate AA or Aa.
• Examine parent-offspring pairs: parents with free earlobes producing attached offspring must carry recessive allele (Aa).
• Check individuals 1 and 7: both show free earlobes but have aa children, requiring Aa genotype.
• Rule out others: no aa offspring from 3,4,5,6,8,9 or no definitive heterozygote evidence.

Why A is correct:

• Individuals 1 and 7 have dominant phenotype but transmit recessive allele to offspring, per Mendel's law of segregation, confirming Aa.

Why the others are wrong:

• B: 3 and 4 could be AA, as their offspring lack aa.
• C: 5 and 8 show no aa offspring, allowing AA possibility.
• D: 6 and 9 lack evidence of recessive transmission.

Final answer: A