Problem 7 - Biology: The Unity and Diversity of Life

Question

Color blindness is a case of __________ inheritance. a. autosomal dominant c. \(X\) -linked dominant b. autosomal recessive d. X-linked recessive

Step-by-Step Solution

Answer

Color blindness is usually X-linked recessive inheritance.

Step 1: Understand the Question

The question is asking us to identify the type of genetic inheritance responsible for color blindness from the given options.

Step 2: Review Genetic Inheritance Types

Autosomal dominant and recessive inheritance affects genes on the non-sex chromosomes, whereas X-linked dominant and recessive inheritance affects genes on the X chromosome.

Step 3: Identify the Pattern of Color Blindness

Color blindness is commonly known to be inherited in a pattern linked to the X chromosome, making it a sex-linked trait.

Step 4: Analyze the X-linked Options

We know color blindness is X-linked, so it must be either X-linked dominant or X-linked recessive. Most forms of color blindness, particularly red-green color blindness, are X-linked recessive.

Step 5: Final Step: Select the Correct Option

Based on our analysis, color blindness is most commonly inherited as X-linked recessive. Therefore, the correct answer is option (d).

Key Concepts

color blindness

Color blindness is a condition where a person cannot see colors in the usual way. This usually affects their ability to distinguish between certain colors—most commonly, reds and greens. This happens because of issues with the light-sensitive cells in the eye. These are called cones, and they are found in the retina.

People with color blindness see fewer colors than others do or mix up certain colors. For example, red might look like brown or more similar to green.

Color blindness differs in severity and can be mild or severe depending on how much the cones are affected. It is important to note that this is not a type of blindness but a different way of seeing colors.

genetic inheritance

Genetic inheritance refers to how genetic traits are passed from parents to their offspring. Every individual has

• 46 chromosomes, arranged in 23 pairs.
• Two of these chromosomes come from each parent.

The genes located on these chromosomes determine various traits such as eye color, hair color, and the potential to inherit certain conditions, like color blindness.

Genes come in different versions called alleles, and they determine traits through their interactions. Traits can be "dominant" or "recessive." A dominant trait is one where only one allele is needed for it to be expressed, whereas a recessive trait requires both alleles to be present.

This foundation helps explain how conditions like color blindness can pass from one generation to the next.

X chromosome

The X chromosome is one of two sex chromosomes, the other being the Y chromosome. Together, these determine a person's biological sex. Women typically have two X chromosomes (XX), while men have one X and one Y chromosome (XY).

The X chromosome carries many genes crucial for development and functioning. Problems or mutations in any of these genes can lead to various genetic conditions, including color blindness. Because women have two X chromosomes, they are less likely to have X-linked recessive conditions. If one X chromosome carries the mutation, the other X can often compensate. However, men, with only one X chromosome, will express the condition if their single X has the mutation.

This means that X-linked conditions, like color blindness, often affect men more frequently than women.

sex-linked trait

A sex-linked trait is a characteristic determined by genes located on the sex chromosomes. These traits can be linked to either the X or Y chromosome but are more commonly associated with the X because it is larger and contains more genes.

Some characteristics of X-linked traits include:

• They often follow a specific pattern of inheritance, where conditions are more commonly seen in males.
• Females can be carriers, meaning they have the gene for the trait but do not necessarily express it.
• In the case of females, one out of two X chromosomes can carry the gene, whereas in males, their single X chromosome shows the effect if it has the gene.

Color blindness is a classic example of an X-linked recessive trait, meaning those without a second normal X chromosome to "mask" the effect of the genetic change—often males—will express the trait.