Final answer:
To find the probability of a recessive phenotype with a 2/3 probability of being heterozygous, you multiply the chance of receiving a recessive allele from each parent (1/3). The outcome is 1/9, which means the correct answer is D) By 1/3, 1/9.
Step-by-step explanation:
To determine the probability of having a recessive phenotype when the probability of being heterozygous is 2/3, we must first know the potential genotypes of the organism. Since a heterozygous organism (Aa) does not display the recessive phenotype, we are interested in the probability of an organism being homozygous recessive (aa). Assuming a simple Mendelian trait, the only way to have a recessive phenotype is for an organism to receive two recessive alleles.
Let's use the provided information about second order genetics and probabilities. If an organism has a 2/3 chance of being heterozygous (Aa), it means there is a 1/3 chance of it being homozygous dominant (AA) or homozygous recessive (aa). The probability of the organism being homozygous recessive (and thus expressing a recessive phenotype) is calculated by multiplying the probability of receiving a recessive allele from one parent (1/3) with the probability of receiving a recessive allele from the other parent (1/3), which equals (1/3) × (1/3) = 1/9. Therefore, the correct answer is D) By 1/3, 1/9.