Genetics and Plant Breeding

It is a cross of F₁ hybrid with dominant parent.

Phenotypic ratio in a dihybrid cross is 9:3:3:1 this means 9 and 1 are parental, 3 and 3 are non-parental recombinant, so total parental is 10 and total recombinant is 6 thus ratio is 10/6 i.e 5:3.

It states that the two factors of a character segregate at the time of gamete formation and then reunite at the time of fertilisation. it is also known as law of purity of gamete.

More than two alternative forms of gene, present on same locus are called multiple alleles.

In all of the above, the gene of allelomorphic pair are neither regarded as dominant nor recessive, but both of them express themselves partially in hybrid. Genotypic and Phenotypic ratio is the same.

As per detailed investigation by S.Blixt on pea plant ,  7 selected characters were located on following chromosome -   stem height on chromosome number 4, flower colour on chromosome number 1, flower position on  chromosome number 4, pod shape on chromosome number 4, pod colour on chromosome number 5, seed shape on chromosome number 7 and seed colour on chromosome number 1.

It causes death of organism in homozygous recessive state.

It is the phenotypic ratio for dominant epistasis, for eg. fruit color in summer squash.

Heterozygosity is always inherited because of recessive gene.

In recessive epistasis phenotypic ratio is 9 : 3 : 4 and genotypic ratio is 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1. So if we count, the total is 12.

Emerson and East studied polygenic inheritance in case of cob length in maize.

A cross or shade (of any type) in the symbol signifies the carrier or recessive allel.

Number of phenotypes in polygenic inheritance is calculated by = ( 2 x n ) + 1, where n is number of pairs of polygene. As human skin color is controlled by 3 pairs of polygenes, thus number of phenotypes = ( 2 x 3 ) + 1 = 7. Also, phenotypic ratio for human skin color is 1 : 6 : 15 : 20 : 15 : 6 : 1. So, if counted, the answer is 7.

Contribution of each gene = (maximum wt - minimum wt ) / number of polygene: (260 - 200 ) / 6 = 10, weight of progeny = ( number of dominant gene x contribution of each gene ) + minimum value. Thus, number of dominant gene in progeny = 2 (AaBbcc), weight of progeny = ( 2 x 10) + 200 = 220.

According to hardy - weinberg equation, p refers to frequency of dominant allele and q refers to frequency of recessive allele. p = 0.6 and q = 0.4 Thus, frequency of heterozygous carrier = 2pq = 2 x 0.6 x 0.4 = 2 x 0.24 =0.48.