Dihybridism, interaction of non-allelic genes, polyhybridism

Dihybridism

 * Dihybridism = during the hybridization experiment, we simultaneously monitor the phenotype manifestations of 2 genes.
 * the term was introduced by de Vries (1900)
 * the rule of independent combination of traits applies = the probability that 2 random phenomena occur simultaneously is the product of the probability of occurrence of each of them for the crossing of organisms differing in 2 pairs of alternatives signs
 * applies to genes located on different chromosomes.
 * if they are genes located on 1 chromosome, they must be far enough apart, to not apply gene binding


 * genotype's cleavage ratios:
 * 1:2:1:2:4:2:1:2:1 (F2 generation)
 * 1 : 1 : 1 : 1 (Bc)
 * phenotype's cleavage ratios:
 * 9 : 3 : 3 : 1 (F2 generation)


 * P generation:
 * AABB x aabb nebo AAbb x aaBB
 * uniform offspring (F1 generation)
 * genotype AaBb


 * v F2 generaci
 * 9 /16 individuals with dominant phenotype in both traits (AaBB, AaBb, AABB, AABb)
 * 3 /16 individuals with dominant phenotype in one trait (Aabb, AAbb)
 * 3 /16 individuals with recessive phenotype in one trait and dominant in the 2nd trait
 * 1 /16 individuals with both recessive traits (aabb)


 * with incomplete dominance, 3 phenotypic manifestations appear in the F2 generation – dominant, intermediate and recessive

Interaction of non-allelic genes

 * if 1 phenotypic trait is conditioned by multiple genes, deviations in cleavage ratios will appear
 * for describing non-allelic gene interactions:

Epistasis

 * = superiority of a certain genotype of one gene over the genotype of another gene
 * one-sided interaction
 * 12 : 3 : 1 (F2 generation)
 * 2 : 1 : 1 (Bc)
 * 1) dominant = suppression of expression of the hypostatic gene by dominant alleles of the epistatic gene
 * 2) recessive = recessive allele of an epistatic gene suppresses in the homozygous state the phenotypic expression of the second gene regardless of its genotype (aa > B i b)

Hypostasis

 * = recessiveness
 * 9 : 3 : 4 (F2 generation)
 * 1 : 1 : 2 (Bc)

Complementation

 * = the emergence of a certain trait must be complemented by the effects of the dominant alleles of both genes
 * 9 : 7 (F2 generation)
 * 1 : 3 (Bc)

Duplicate genes

 * = we cannot distinguish the phenotypic expression of one gene from another
 * 1) non-cumulative = for duplicate genes to interact, one allele of either locus is sufficient for full expression of the dominant trait
 * 2) cumulative = cumulative effect of incompletely dominant alleles of both locus (loci)

Polyhybridism

 * tracking many signs
 * F1 consists of 2n gametic combinations (n = number of non-allelic genes) - types of gametes
 * the number of possible genotypic combinations is 3n (the offspring of a monohybrid form 3 different phenotypic classes)

related articles

 * Monohybridism
 * Parental, F1, F2 generation
 * Allelic interactions
 * Genotype
 * Phenotype
 * Backcrossing