Among heritable diseases, which genotype can be present in an individual without causing a disease phenotype in that individual? a. heterozygous for a dominant disease; b. homozygous for a dominant disease; c. heterozygous for recessive disease; d. homozygous for a recessive disease e. all of the above

Verified step by step guidance

1. Understand the concept of dominant and recessive genes. A dominant gene is one where only one copy (allele) is needed for the trait or disease to be expressed. A recessive gene requires two copies (one from each parent) for the trait or disease to be expressed.
2. Analyze option a: heterozygous for a dominant disease. This means the individual has one dominant allele and one recessive allele. Since the disease is dominant, the presence of one dominant allele is enough to express the disease phenotype.
3. Analyze option b: homozygous for a dominant disease. This means the individual has two copies of the dominant allele. Since the disease is dominant, having two copies will definitely express the disease phenotype.
4. Analyze option c: heterozygous for a recessive disease. This means the individual has one recessive allele and one dominant normal allele. The disease phenotype is not expressed unless there are two recessive alleles.
5. Analyze option d: homozygous for a recessive disease. This means the individual has two recessive alleles. Since the disease is recessive, having two copies will express the disease phenotype.

Key Concepts

Dominant and Recessive Alleles

In genetics, alleles can be classified as dominant or recessive. A dominant allele expresses its trait even when only one copy is present (heterozygous), while a recessive allele requires two copies (homozygous) to express its trait. Understanding this distinction is crucial for determining how genotypes relate to phenotypes in heritable diseases.

Genotype vs. Phenotype

Genotype refers to the genetic makeup of an individual, while phenotype is the observable expression of that genotype. An individual can carry a genotype that does not manifest as a disease phenotype due to the nature of the alleles involved, particularly in the case of recessive diseases where a single dominant allele can mask the effect of a recessive one.

Heterozygous and Homozygous Conditions

Heterozygous individuals have two different alleles for a particular gene, while homozygous individuals have two identical alleles. In the context of heritable diseases, being heterozygous for a recessive disease means the individual carries one normal allele and one disease allele, which typically does not result in the disease phenotype, unlike homozygous conditions that often do.