Question

The genotype that causes fair skin complexion in human is

• A. AABBCC
• B. AaBbCc
• C. aabbcc
• D. aaBBcc

Hint:

More dominant alleles (A, B, C) → More melanin → Darker skin; All recessive alleles (aabbcc) → Least melanin → Fair skin

Answer 1

The Correct Option is C

Skin complexion in humans is a polygenic trait controlled by multiple alleles at different loci (typically A/a, B/b, and C/c). The dominant alleles (A, B, C) contribute to higher melanin production, resulting in darker skin tones. Recessive alleles (a, b, c), on the other hand, contribute less or no melanin production.
The genotype aabbcc lacks all the dominant alleles responsible for increased melanin synthesis. Therefore, individuals with this genotype have the least melanin, resulting in fair skin.
- AABBCC = darkest skin
- AaBbCc = intermediate skin tone
- aabbcc = fair skin

Answer 2

Step 1: Understand the nature of skin complexion inheritance
Human skin complexion is a classic example of a polygenic trait, which means it is controlled by multiple genes rather than a single gene. These genes work together to determine the overall pigmentation of the skin.

Step 2: Role of multiple genes and alleles
Each gene involved in skin color typically has two or more alleles, where some alleles contribute to darker pigmentation and others contribute to lighter or fairer pigmentation. The combined effect of all these genes results in the wide variation of skin tones observed in humans.

Step 3: Explanation of the genotype "aabbcc"
The genotype "aabbcc" indicates that the individual is homozygous recessive at three different gene loci. This means the person has inherited the recessive allele from both parents for each of these genes.
- The recessive alleles (represented by lowercase letters) are associated with lighter pigmentation.
- When combined (aabbcc), these recessive alleles have a cumulative effect that leads to fair skin complexion.

Step 4: Why homozygous recessive leads to fair skin
- Dominant alleles (capital letters) typically produce more melanin, resulting in darker skin.
- Recessive alleles produce less melanin or reduce melanin production.
- The presence of all recessive alleles in homozygous form reduces melanin synthesis significantly, causing fair skin.

Step 5: Importance of polygenic inheritance in skin color
Because multiple genes influence skin color, the genotype "aabbcc" is just one possible combination that leads to fair skin. Other combinations with more recessive alleles at different loci can also produce similar effects.

Step 6: Final conclusion
Thus, the genotype "aabbcc" causes fair skin complexion due to the combined recessive alleles at multiple gene loci that reduce melanin production, illustrating the polygenic nature of human skin color.