Question

The alleles found in haploid organisms cannot be dominant or recessive. Why? a. Dominance and recessiveness describe which of two possible phenotypes are exhibited when two different alleles occur in the same individual. b. Because only one allele is present, alleles in haploid organisms are always dominant. c. Alleles in haploid individuals are transmitted like mitochondrial DNA or chloroplast DNA. d. Most haploid individuals are bacteria, and bacterial genetics is completely different from eukaryotic genetics.

Short answer

In haploid organisms, the concept of dominance and recessiveness is not applicable because they have only one set of chromosomes and one allele for each gene. Dominance and recessiveness describe which of two possible phenotypes are exhibited when two different alleles occur in the same individual. Since haploid organisms have just one allele for each gene, there are no pairs of alleles to determine dominance or recessiveness, and only one possible phenotype can be expressed for each gene.

Step-by-step solution

Haploid organisms have only one set of chromosomes. This means that they have only one allele for each gene. Examples of haploid organisms include bacteria and certain stages of the life cycle of some eukaryotes like fungi and algae. #Step 2: Explain the difference between dominant and recessive alleles#

In diploid organisms, which have two sets of chromosomes, each individual has two alleles for each gene. Dominant alleles are those that determine the phenotype (observable characteristics) of an individual even when there is only a single copy of that allele present. Recessive alleles, when present together with a dominant allele, do not have an impact on the phenotype, but when two copies of a recessive allele are present, they determine the phenotype. #Step 3: Identify the correct explanation#

The correct explanation for why the alleles found in haploid organisms cannot be dominant or recessive is option (a): Dominance and recessiveness describe which of two possible phenotypes are exhibited when two different alleles occur in the same individual. #Step 4: Explain the correct explanation in detail#

Since haploid organisms have only one allele for each gene, there are no pairs of alleles to determine the concept of dominance or recessiveness. The concept of dominant and recessive alleles only applies to diploid organisms because it describes how different alleles interact and influence the phenotype when present together. In haploid organisms, only one possible phenotype can be expressed for each gene because there is only one allele present, so there is no scenario in which dominance or recessiveness is relevant.

Key concepts

Dominance and Recessiveness

Understanding the concepts of dominance and recessiveness is crucial when studying genetics. In the realm of diploid organisms, which possess two sets of chromosomes, genes exist in pairs of alleles. Each organism inherits one allele from each parent. When two different alleles are present, their interaction determines the outcome of a trait. A dominant allele masks the effects of a recessive allele in heterozygous pairings, meaning if one dominant and one recessive allele are present, the trait associated with the dominant allele will be expressed.

In more simple terms, think of the dominant allele as a loud voice that drowns out the softer voice of the recessive allele. The presence of a dominant allele (A) alongside a recessive allele (a), often written as Aa, will result in the phenotype associated with the dominant allele. It's only when two recessive alleles (aa) pair together that the recessive trait can be expressed, given there's no 'louder voice' to suppress it.

Alleles in Haploid Organisms

The genetic makeup of haploid organisms presents an entirely different scenario. Haploid organisms, such as bacteria and certain fungi and algae in specific life stages, only have one set of chromosomes. This means there's just a single allele for each gene, eliminating the possibility of dominant or recessive interaction, as there's no pair for any allele to interact with.

Consider chromosomes like pages in a book. In haploid organisms, there's only one page per chapter, so there's no alternative narrative to consider. The single allele present dictates the phenotype directly without any contest. As a result, when exploring haploid genetics, we don't reference dominance or recessiveness because these terms hinge on the interaction of allele pairs, which in haploid organisms, simply does not exist.

Phenotype Expression

Phenotype expression is the observable manifestation of an organism's genetic makeup, including physical characteristics, behavior, and biochemical traits. In diploid organisms, this expression is the result of the interaction between two alleles for each gene. However, in haploid organisms, phenotype expression is straightforward: the only allele present automatically dictates the trait.

For educational clarity, imagine phenotype expression as a single performer on stage—no duets, no ensemble, just a solo act. What you see and get is the direct result of this performer’s act (the effect of the single allele present), with no hidden variation or genetic tug-of-war. This simplicity allows us to predict and understand the traits of haploid organisms without considering nuanced allele interactions as in diploid organisms.