Dihybrid Cross and 9:3:3:1 Ratio — NEET Biology
✅ Asked in NEET 2023In the dihybrid cross, the phenotypes round,yellow; wrinkled, yellow; round, green and wrinkled, green appeared in the ratio 9:3:3:1. Such a ratio was observed for several pairs of characters that Mendel studied.
A dihybrid cross involves two traits controlled by different genes. When both parents are heterozygous (AaBb), the offspring show four phenotypes in a 9:3:3:1 ratio: 9 dominant-dominant, 3 dominant-recessive, 3 recessive-dominant, and 1 recessive-recessive. Students often confuse this with monohybrid ratios (3:1) or forget that this ratio only appears when genes assort independently (on different chromosomes). To get it right: always draw a Punnett square for dihybrids, recognize that 9:3:3:1 indicates independent assortment, and remember the 16 possible combinations from gamete combinations. This fundamental concept is tested repeatedly as it proves Mendel's law of independent assortment.
Match List – I with List – II. (NEET 2023) List – I (A) Monohybrid Cross (B) Dihybrid Cross (C) Incomplete dominance (D) Test Cross List – II (I) 1 : 1 (II) 1 : 2 : 1 (III) 3 : 1 (IV) 9 : 3 : 3 : 1
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