Skip to content
Login Register

#phenotypic classes

3 public questions tagged with this topic.

Gene intraction

Which interaction produces 3 phenotypic classes?

Dominant epistasis emerges when dominant allele at one locus inhibits expression of second locus irrespective of its genotype, acting as dominant suppressor or inhibitor. In summer squash white fruit gene W masks yellow gene Y, producing twelve white fruits carrying W, three yellow with ww Y_, and one green with ww yy, giving 12:3:1 distribution. This three-class pattern distinguishes dominant epistasis from duplicates giving two classes or recessive epistasis giving 9:3:4. Recognising twelve as largest class signals dominant inhibitor acting upstream in pigment biosynthetic pathway blocking downstream colour manifestation.

Ref: Strickberger, Genetics, 3rd ed., Chapter 6: Dominant Epistasis 12:3:1 Ratio Three Classes

View Details
Gene intraction

In gene interaction, total phenotypic classes are usually

Gene interaction merges phenotypic classes rather than creating novel ones because underlying genotypic segregation from independent assortment remains 9:3:3:1 while phenotypic translation changes due to pathway convergence. When two loci affect same developmental process, some genotypic combinations become phenotypically indistinguishable through masking or requirement for both dominant alleles. Complementary interaction collapses three genotypic groups containing recessive homozygotes into single white class yielding two phenotypes 9:7, duplicate dominant collapses all but double recessive yielding 15:1. Thus total distinct phenotypes never exceeds four Mendelian classes and usually appears same or fewer.

Ref: Snustad & Simmons, Principles of Genetics, 7th ed., Chapter 4: Gene Interaction Reduces Phenotypic Classes

View Details
Genetic Crosses

A dihybrid cross AaBb × AaBb produces how many phenotypic classes in F2?

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

View Details