Inheritance from parents to the offsprings has certain patterns. Several Inheritance pattems that will be studied are non-Mendelian inheritance, Linkage , crossing over, non-disjunction, Iethal gene, blood type, and sex determination.
According to Mendel's law, phenotypic ratio of F, generations in dihybrid cross is 9 : 3 : 3 : 1. However, in several cases the phenotypic ratio of F, generation does not match Mendel's law. Nevertheless, the ratio that appears still ranges in 9 : 3 : 3 : 1. For example, 15 : 1 or (9 + 3) : I and 12 : 3: 1 or (9 + 3) : 3 : 1. This condition is called non-Mendeli'an inheritatnce. Several cases of non-Mendelian inheritance are gene interaction between loci- epistasis-hypostasis, polygenic, and cryptomeri.
Gene Interaction between locus
Gene interaction between loci may produce different phenotypic Ratio of F2, generation with Mendel's law. It occurs when one trait is Determined by non-homologous genes lied in different locus. For example, the genes that determine comb shape. The shape of chicken comb is determined by two pairs of alleles located in different locus, R, r, and P, p. Allele -R determines the structure of rose comb and is Dominant to recessive allele r. Allele r determines the structure of single comb. Allele P determines the structure of pea comb and is dominant to recessive allele p. Allele p determines the structure of single comb.
in an organism, when the allele R appears at the same time with allele P, interaction between the two alleles occurs and produces new trait, walnut. If the allele r and allele p appear at the same time without the presence of either allele dominant.R or P, the interaction that occurs produces new trait, single comb. Rose comb will appear if the presence of allele .R is not at the samd time with that of allele P. Pea comb is created if the appearance of allele P is not at the same time with that of allele R.
Phenotypic ratio in Picture
|Interaction between genes causes the appearance of new phenotype|
is similar to the one in regular dihybrid cross. However, the interaction between genes has produced phenotypic disorder in F, and F, generations so that the appearing phenotype is different from the parents. The prove is the appearance ofnew phenotypes wich are walnut comb and single comb.
|The genotype for chicken comb types|
|Type of chicken comb a walnut comb b rose comb c pea comb d single comb|
Type of chicken comb a walnut comb b rose comb c pea comb d single comb
source: Biology, The unity and Diversity of life, 2004