Which of the following describes the genotype and phenotype of parents whose child will definitely have a recessive trait?
A. Both parents are homozygous for the recessive allele and have the trait.
B. Both parents are homozygous for the recessive allele but do not have the trait.
C. Both parents are heterozygous for the recessive allele and have the trait.
D. Both parents are heterozygous for the recessive allele but do not have the trait.
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To determine the genotype and phenotype of parents whose child will definitely have a recessive trait, we need to understand the inheritance pattern of traits.
In general, traits are determined by genes, which come in pairs called alleles. Each parent contributes one allele to their offspring, and the combination of these alleles determines the genotype and phenotype of the child.
In this case, a recessive trait means that the trait is expressed when an individual has two copies of the recessive allele. On the other hand, a dominant trait is expressed when an individual has at least one copy of the dominant allele.
Based on this information, we can analyze each option:
A. Both parents are homozygous for the recessive allele and have the trait.
If both parents have the trait, they must have at least one copy of the recessive allele. If they are homozygous for the recessive allele, they will only pass on the recessive allele to their child. Thus, the child will have the recessive trait. This option is a possibility.
B. Both parents are homozygous for the recessive allele but do not have the trait.
If both parents do not have the trait, it means they do not have any copies of the dominant allele. If they are homozygous for the recessive allele, they will only pass on the recessive allele to their child. Therefore, the child will also not have the trait. This option is not a possibility.
C. Both parents are heterozygous for the recessive allele and have the trait.
If both parents have the trait and are heterozygous (having one copy of the recessive allele and one copy of the dominant allele), they can pass on either the dominant or the recessive allele to their child. Since having at least one copy of the dominant allele prevents the expression of the recessive trait, it is not guaranteed that the child will have the recessive trait. This option is not a possibility.
D. Both parents are heterozygous for the recessive allele but do not have the trait.
If both parents do not have the trait, it means they do not have any copies of the dominant allele. Being heterozygous for the recessive allele means they have one copy of the recessive allele. Therefore, they will pass on the recessive allele to their child, making it certain that the child will have the recessive trait. This option is a possibility.
Thus, the correct option is D. Both parents are heterozygous for the recessive allele but do not have the trait.
1. B
2. A
3. B
4. D
5.C