What will be the probability of non-parental offsprings in the F2, generation of a
quantitative character regulated by two genes
Answers
Answer:
Explanation:
Mendel believed that a factor or gene is responsible for the expression of one character. This factor or gene has two alternate forms or alleles.
The flower colour in his peas were either red or white, the seeds either yellow or green, either smooth or wrinkled etc.
These qualitative characters permitted Mendel to make accurate counts of individuals showing one or the other of these alternative traits. For instance, if tall and dwarf plants were crossed, in F1
only tall plants and in F2
, only tall and dwarf plants were obtained. No plants of intermediate types were ever obtained. Such type of inheritance based on Mendelian ratio is known as qualitative inheritance.
On the other hand, when two or more genes at different loci are responsible for the expression of one character, such genes are known as polygenes or multiple genes and the character or trait they produce is called a polygenic trait.
The inheritance pattern involving multiple genes is known as polygenic or quantitative inheritance. The quantitative traits in man include its height, weight, intelligence and colour and those of plants include their size, shape, number of seeds and fruits etc.
The quantitative traits are also called metric traits. In quantitative inheritance, the offspring’s do not show clear cut differences among them, rather show intermediate character of two parents. The gradations in characters are determined by a number of genes and all the genes have additive effect or are cumulative. It means that each gene has a certain amount of effect, and more is the number of dominant genes, the more is the degree of expression of the character.
Nilsson-Ehle (1908) made a very interesting study on the colour of grain in wheat. He crossed red kerneled variety with white kerneled strain and obtained F1
plants whose grains were uniformly red but intermediate between red and white parental generations. When the members of F1
were self-crossed five different phenotypic classes appeared in F2
in the ratio of 1: 4: 6: 4: 1.
(i) Red (extreme) – 1/16
(ii) Dark red – 4/16
(iii) Medium red – 6/16
(iv) Light red – 4/16
(v) White – 1/16
Later it was found that the kernel colour in wheat is determined by two pairs of genes Aa and Bb. Genes A and B are dominant genes which determine the red colour whereas a and b are recessive alleles. Results of this polygenic inheritance is depicted in Fig. 5.8.
r
Answer:14/16
Explanation:because in Mendelian cross parental characters resembles more in F1 generation and non parental n F2 only two character will match to parental