Question

Write a one-sentence definition of the term "genotype." Do the same for "phenotype." Does the phenotype of an organism automatically change when a change in genotype occurs? Why or why not? Can phenotype change without a change in genotype? In both cases, give examples to support your answer. (Section 10.1)

Short answer

Genotype is an organism's genetic makeup; phenotype is its observable traits. Phenotype does not automatically change with genotype, and it can change solely due to environmental factors.

Step-by-step solution

Define Genotype

A genotype is the genetic makeup of an organism, consisting of the specific set of alleles it possesses.

Define Phenotype

A phenotype is the observable traits or characteristics of an organism, which result from the interaction of its genotype with the environment.

Consider whether phenotype changes with genotype

No, the phenotype of an organism does not automatically change when a change in genotype occurs. While genotype is a factor, the environment also plays a crucial role in determining phenotype. For example, identical twins (with the same genotype) can have different phenotypes if they are raised in different environments.

Can phenotype change without a change in genotype?

Yes, the phenotype can change without a change in genotype due to environmental influences. For instance, a person's skin may tan from sun exposure even though their genotype remains the same.

Key concepts

Genetic Makeup

Genetic makeup refers to the unique set of genes that an organism carries. These genes are made up of DNA sequences and determine the hereditary traits passed from parents to offspring.
Each individual has two sets of genes, one from each parent, and these combine to form the organism's genotype.
For example, if you inherit a gene for blue eyes from one parent and a gene for brown eyes from the other, this combination is part of your genetic makeup.
The exact combination of these genes influences various characteristics, from hair color to susceptibility to certain diseases.

Observable Traits

Observable traits, also known as phenotype, are the physical expressions of an organism's genes. These traits are visible characteristics like eye color, height, and skin tone.
However, not all observable traits are purely genetic; many are also influenced by environmental factors.
For example, while two people may have genes for a tall height, their actual height can be influenced by nutrition and health during their growth periods.
Therefore, observable traits are often a mix of genetic predisposition and environmental influences.

Environmental Influence

The environment plays a significant role in shaping an organism's phenotype. Environmental factors include everything from the climate and food availability to social conditions and chemical exposures.
For instance, identical twins may have the same genetic makeup but can become quite different if one receives better nutrition or lives in a different climate.
Another classic example is the tanning of the skin due to sun exposure. Even if two people have the same genotype for skin color, varying degrees of sun exposure will result in different levels of tanning, thus different phenotypes.

Alleles

Alleles are different versions of a gene that determine specific traits. For instance, the gene responsible for eye color has different alleles that result in blue, green, or brown eyes.
Every individual inherits two alleles for each gene—one from each parent. The combination of these alleles determines the trait expressed.
Some alleles are dominant, meaning they will express the trait even if only one copy is present. Others are recessive and require two copies to affect the phenotype.
For example, the allele for brown eyes is dominant, while the allele for blue eyes is recessive. Therefore, a person with one allele for brown eyes and one for blue eyes will typically have brown eyes.

Genotype-Phenotype Interaction

The interaction between genotype and phenotype is complex and influenced by both genetic and environmental factors. The genotype provides the blueprint, but the environment can modify, enhance, or suppress these genetic instructions.
For example, a person may have a genetic predisposition to be tall, but if they suffer from malnutrition, they may not reach their potential height.
Likewise, certain genetic conditions, such as phenylketonuria (PKU), can be managed and minimized through dietary adjustments, showing that while the genotype sets the potential, the environment can alter the outcome.
Therefore, understanding both genetic makeup and environmental influences is crucial for comprehending how traits and characteristics develop.