Genetic Variation in Offspring — NEET Biology

Correct answer: B — S2 and S3 only

The core concept is the basis of variation in polygenic traits, specifically why siblings can have different skin tones. Let's evaluate each statement: S1: Skin tone is a polygenic trait, meaning it's controlled by multiple genes, not primarily by single gene Mendelian dominance. Mendelian traits typically show discrete expression, unlike the continuous variation of skin tones. So, S1 is incorrect. S2: Polygenic inheritance, involving multiple genes with additive effects, is fundamental to the continuous variation observed in traits like skin colour. Different combinations of these multiple genes passed from parents to offspring result in varying phenotypes. So, S2 is correct. S3: During meiosis, independent assortment of chromosomes and recombination (crossing over) shuffle alleles from multiple genes, creating a vast diversity of gametes. When these diverse gametes combine during fertilization, it leads to unique combinations of alleles in offspring, thus generating a continuous range of phenotypes for polygenic traits. So, S3 is correct. S4: While environmental factors (like sun exposure) do influence skin tone, genetic variation due to polygenic inheritance is the primary underlying reason for the *spectrum* of skin tones observed among siblings. Environmental factors modify the genetically determined potential, they don't solely cause the wide spectrum in a family without genetic differences. So, S4 is incorrect. S5: Crossing over (recombination) is a process that increases genetic variation, including for polygenic traits. The absence of crossing over at the centromere is a specific detail and not the *main* or sole reason for phenotypic differences in polygenic traits; rather, it is the overall genetic recombination and independent assortment of multiple genes that contribute to diversity. So, S5 is incorrect. Therefore, statements S2 and S3 are correct. Option A is incorrect because S1 and S4 are false. Option C is incorrect because S1 and S5 are false. Option D is incorrect because S4 and S5 are false. The correct option is B because only S2 and S3 are correct.