Principles of Inheritance and Variation Test - 1

After hybridization of RRYY and rryy genotypes, where two genes R and Y are located very close, the chance of recombination are reduced therefore, they will be linked together and thus there will be higher number of parental types.

Gregor Mendel, conducted hybridisation experiments on garden peas for seven years (1856 – 1863) and proposed the laws of inheritance in living organisms. He proposed 3 laws of inheritance: 

(i) Law of dominance 
(ii) Law of segregation 
(iii) Law of independent assortment

The off springs show 27 : 9 : 9 : 9 : 3 : 3 : 3 : 1 ratio is found in trihybrid cross.

The term “chromosome” was first suggested in 1888 by the German anatomist Heinrich Wilhelm Gottfried von Waldeyer-Hartz. He used the term to describe certain structures that from during the process of cell division (reproduction).

This is the duplicate gene interaction which exhibits 15 : 1 ratio.

• Cytoplasmic inheritance is due to extranuclear genes present in mitochondria and chloroplasts.
• These genes do not follow Mendelian inheritance.
• The cytoplasm is nearly absent in male sperms but is abundantly present in the female egg.
• So cytoplasmic inheritance is of maternal effect.

According to this law genes of two characters not interfere with the transmission of each other. In other words the inheritance of genes of two or more characters occur independent of each other. But this is not for the gene located on the same chromosomes showing linkage. Hence linkage disproves the law of independent assortment.

Epistasis takes place when the effects of one gene are modified by one or several other genes, which are sometimes called modifier genes. The gene whose phenotype is expressed is said to be epistatic, while the phenotype altered or suppressed is said to be hypostatic. Epistasis can be contrasted with dominance, which is an interaction between alleles at the same gene locus.