Tag: genetics

Mirabilis jalapa is a plant showing incomplete dominance which means that when in F$ _1$ generation intermediate phenotype appears instead of the two parent phenotypes. 

A.Heterozygotes – Organisms with a pairs of contrasting characters are called Heterozygotes.

B.Alleles - An alternative form of a character in a pair, controlled by a single gene is called Allele. It is dominant either in homozygous or heterozygous state.

C.Complementary gene – Two genes present on separate loci that interact together to produce a dominant phenotype is called Complementary gene. In the F₂ generation 9:7 ratio.

D.Supplementary gene – genes which include two pairs of non-allelic genes. Both of them are involved in affecting the same character. Out of the non-allelic genes, one gene is dominant and can express by itself. Second gene is also dominant but expresses only when it is supported by the presence of the first gene. In the F₂ geneartion 9:3:4 ratio.

So, the correct option is ‘Alleles’. 

class=A cross is made between pure yellow flowered  and round fruit(YYRR) with white flowered elongated fruit(yyrr). In the F1 generation 20 progeny with yellow flowered and round fruits(YyRr) are formed. When they are subjected to self pollination followed by self fertilization, in the F2 generation, 960 progeny are formed. In these 540 plants are yellow flowered round fruits, plants are yellow flowered elongated fruits, 180 fruits are white flowered round fruits and 60 plants are white flowered elongated fruits the correct option is 20, 540

A.Supplementary genes – A pair of non allelic genes, one of which produces its effect independently in the dominant state while the dominant allele of the second gene is without any independent effect but is able to modify the effect of the former to produce to a new trait are called Supplemetary genes. Due to these genes in the F₂ generation, 9:3:4 ratio of progeny are obtained. It is a modified Mendel dihybrid ratio.

B.Complementary genes – Two genes present on separate loci that interact

together to produce dominant phenotypic character; neither of them if present alone can express itself are called complementary genes. Due to these genes in the F₂ generation, 9:7 ratio of progeny are obtained. It is a modified Mendel dihybrid ratio.

C.Lethal genes – A pair of genes present in the homozygous conditions, causes the death of the individual are called Lethal genes. Due to the genes, in F₂ generation 2:1 ratio of progeny are obtained.

D.Epistatic genes – A gene which masks the action of another gene is termed as epistatic gene and process is called epistasis. Due to these genes in the F2 generation, either 9:3:4  or 12.3.1 ratio of progeny are obtained. It is a modified Mendel dihybrid ratio.

So, the correct option is ‘supplementary genes’.     

Pleiotropy occurs when one gene will code and control the phenotype or expression of several different and unrelated traits. Phenylketonuria is an autosomal recessive disorder controlled by a mutant gene present on the 12th chromosome. This mutant gene fails to code for the enzyme phenylalanine hydroxylase required for normal metabolism of amino acid phenylalanine to tyrosine. Due to this, there is an accumulation of phenylalanine in body fluids such as blood, sweat, CSF. An abnormal breakdown product phenyl ketone is found in urine A higher level of phenylalanine and pheylketone cause severe brain damage leading to mental retardation. Thus phenylketonuria is the best example to explain pleiotropy.

E.Nilsson – Ehle crossed red kernelled variety with white kernelled variety of wheat. The grains of F₁ were self crossed among themselves, five different phenotypic classes appeared in F₂ showing the ratio of 1:6:15:20:15:6:1.

These scientist found that the kernel colour in wheat is determined by two pairs of genes A and B. It is called polygenic inheritance.

So, the correct option is ‘polygenic inheritance’.

Mutations in the human gene for fibrillin-1 (FBN1) in the Marfan syndrome and related disorders. Mutations in FBN1 produce Marfan syndrome, a pleiotropic autosomal dominant connective tissue disorder with prominent manifestations in the skeleton, eye and cardiovascular system.

When there are three or more alternative forms of a gene, it is called multiple allelism. Polygeny suggests that humans evolved from several different ancestors. When a single gene has more than one effects, it is called pleiotropy.