Dihybridism, interaction of non-allelic genes, polyhybridism

Dihybridism[edit | edit source]

For more information see 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

For more information see Non-allelic gene interactions.

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

= 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)

dominant = suppression of expression of the hypostatic gene by dominant alleles of the epistatic gene
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)

= 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)

non-cumulative = for duplicate genes to interact, one allele of either locus is sufficient for full expression of the dominant trait
cumulative = cumulative effect of incompletely dominant alleles of both locus (loci)

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)

ŠTEFÁNEK, Jiří. Medicine, diseases, studies at the 1st Faculty of Medicine, UK [online]. [cit. 2009]. <http://www.stefajir.cz>.