Marriages between close relatives and cousins is not advisable because

Select incorrect statement

$(A)$ Linked genes cause absolute lethality
$(B)$ Persons affected by $PKU$ do not show mental disorder
$(C)$ $F_{2}$ ratio in codominance and incomplete dominance are same
$(D)$ Sex of male Drosophila is dependent on $Y-$chromosome

How many sentence are correct ?

$(i)$ Every gene contains the information to express a particular trait.

$(ii)$ Gene responsible for $\beta$ - thalassemia is present on $21^{st}$ pair of autosomal chromosome.

$(iii)$ Mendel's approach of using mathematics to explain biological phenomena was totally new and unacceptable to many of the biologists of his time.

What is the correct sequence of the following events

$1.$Formation of the chromosome theory of heredity

$2.$Experiments which proved that $DNA$ is the hereditary material

$3.$Mendel's laws of inheritance-discovery

Code :

Which of the following is true about linkage

$I.$ It is phenomenon in which more recombinants are produced in $F_{2}$-generation

$II.$ More parental combination are produced in $F_{2}$-generation

$III.$ Genotype which are present in $F_{1}$ hybrid. Reappear in high frequency in $F_{2}$-generation

$IV.$ It is a phenomenon in which two chromosome are linked

Select the correct statement: