Match each human phenotypic feature listed on the left with its characteristic variation p… — JAMB UTME

Match each human phenotypic feature listed on the left with its characteristic variation pattern and underlying genetic mechanism on the right.

Human skin pigmentation spectrumContinuous variation governed by polygenic inheritance with environmental modification
ABO blood group classificationDiscontinuous variation controlled by multiple alleles at a single locus
Presence or absence of a widow's peak hairlineDiscontinuous variation governed by simple single-gene (monogenic) Mendelian inheritance
Total dermal ridge count in fingerprintsContinuous variation determined predominantly by additive polygenes with minimal environmental influence

Answer

Human skin pigmentation matches continuous variation governed by polygenic inheritance with environmental modification. ABO blood group classification matches discontinuous variation controlled by multiple alleles at a single locus. Widow's peak hairline matches discontinuous variation governed by simple monogenic Mendelian inheritance. Total dermal ridge count matches continuous variation determined predominantly by additive polygenes with minimal environmental influence.

Continuous traits (such as skin pigmentation and fingerprint ridge counts) form a continuous spectrum of phenotypic values controlled by polygenes, differing in their environmental sensitivity. Discontinuous traits (such as ABO blood groups and widow's peak) form distinct qualitative classes without intermediate phenotypes, controlled by single loci with either multiple alleles or simple Mendelian dominance.

Step-by-Step Solution

Analyze the phenotypic distribution pattern for each feature to classify it as either continuous (quantitative spectrum) or discontinuous (discrete qualitative categories).

Skin pigmentation and dermal ridge count are continuous traits; ABO blood groups and widow's peak are discontinuous traits.

Continuous traits show intermediate gradation across a population, whereas discontinuous traits exhibit distinct non-overlapping phenotypes.

Examine the underlying genetic architecture (monogenic vs. polygenic vs. multiple alleles) for each trait.

Skin pigmentation and ridge count involve polygenes; ABO blood group involves multiple alleles at one locus (

I^A, I^B, i

); widow's peak involves a single monogenic locus.

Polygenic inheritance produces continuous variation through additive effects of multiple genes, whereas single loci yield distinct phenotypic classes.

Evaluate the impact of environmental factors on the expression of each continuous trait.

Skin tone varies significantly with solar radiation exposure (high environmental effect), while finger ridge counts are genetically fixed early in development with minimal environmental susceptibility.

Environmental modification alters phenotypic expression of certain polygenic traits without altering underlying genotype.

Key Concept

Polygenic vs. Monogenic Inheritance and Environmental Influence on Continuous and Discontinuous Variation

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