9 public questions tagged with this topic.
The Law of Segregation explains that recessive traits can be masked in the F1 generation and reappear in the F2 generation.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles
A dihybrid cross with complete dominance results in a phenotypic ratio of 9:3:3:1 in the F2 generation.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Monohybrid Dihybrid and Test Cross
In a monohybrid cross, Mendel observed a phenotypic ratio of 3:1 in the F2 generation.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Monohybrid Dihybrid and Test Cross
The expected genotypic ratio in a monohybrid cross (F2 generation) is 1:2:1 (homozygous dominant: heterozygous: homozygous recessive).
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Monohybrid Dihybrid and Test Cross
The genotypic ratio of a monohybrid cross (F2 generation) is 1:2:1 (homozygous dominant: heterozygous: homozygous recessive).
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Monohybrid Dihybrid and Test Cross
Morgan's experiment crossed heterozygous F1 females carrying coupling configuration of recessive black body b and vestigial vg alleles to homozygous recessive tester males for phenotypic scoring. Unlinked expectation predicts fifty percent parental and fifty percent recombinant phenotypes yet observed parental classes dominated around ninety-eight point seven percent while recombinants rare around one point three percent indicating tight linkage preventing separation. Excess of parental types demonstrated genes reside on same chromosome with infrequent crossover events foundational evidence for chromosomal inheritance and quantitative basis for distance estimation via test cross.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 5: Morgan's Parental Excess 98.7% Demonstration
A dihybrid individual AaBb with unlinked genes can form four gamete types AB, Ab, aB, ab through independent assortment during meiosis. Selfing AaBb x AaBb produces 4x4=16 genotypic combinations collapsed by complete dominance at each locus. Phenotypically, genotype classes group into A-B- displaying both dominant traits, A-bb showing first dominant alone, aaB- second dominant alone, aabb both recessive. Thus four distinct phenotypic classes appear despite nine genotypic classes. Distinction highlights phenotype versus genotype numbers and forms basis for modified ratios when epistasis operates.
Ref: Pierce, Genetics: A Conceptual Approach, 7th ed., Chapter 3: Phenotypic Classes in Dihybrid F2
F2 generation of monohybrid cross Tt by Tt arises from fusion of two gamete types per parent. Four fertilization combinations produce TT once, Tt twice counting both reciprocal fusions, and tt once. Distinguishable genotypic proportions are therefore 1 TT to 2 Tt to 1 tt, genotypic ratio 1:2:1. Phenotypic ratio under dominant expression collapses to 3:1, 1:1 describes test cross, 9:3:3:1 dihybrid, accurate genotypic array reflects equal segregation of alleles and random union maintaining Mendelian expectations. This principle is routinely tested in NEET, CBSE 11-12, CUET, CSIR-NET, GATE and MSc Genetics examinations requiring clear conceptual distinction.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 2: Genotypic Ratio 1:2:1
Selfing heterozygous F1 Tt generates gametic pool with equal frequencies of T and t from each parent. Punnett square combining maternal and paternal gametes yields three genotypic classes TT 25 percent, Tt 50 percent and tt 25 percent. With complete dominance dominance masks heterozygote, tall phenotype encompasses TT plus Tt totaling 75 percent, dwarf tt 25 percent, giving phenotypic ratio 3 tall to 1 dwarf. Genotypic ratio 1:2:1 differs from phenotypic count, 1:1 and 9:3:3:1 correspond to test cross and dihybrid respectively. Cytological correlation with prophase pairing, metaphase alignment and anaphase separation provides visual anchor for memorising genetic laws.
Ref: Snustad & Simmons, Principles of Genetics, 7th ed., Chapter 3: F2 Phenotypic Ratio
