In maize,the chromosome number is $2n = 20$. The number of linkage groups in it shall be:

Which of the following is true about linkage?
$I.$ It is a phenomenon in which more recombinants are produced in $F_{2}$-generation.
$II.$ More parental combinations are produced in $F_{2}$-generation.
$III.$ Genotypes which are present in $F_{1}$ hybrid reappear in high frequency in $F_{2}$-generation.
$IV.$ It is a phenomenon in which two chromosomes are linked.

In a somatic cell,if the arrangement of genes is such that dominant alleles are present on one chromosome and recessive alleles are present on the other chromosome of a homologous pair,what is this arrangement called?

$A$ test cross of an $F_1$ fly $+a/+b$ produces the following offspring:
$++/ab = 9$
$ab/ab = 9$
$+b/ab = 41$
$a+/ab = 41$
What is the distance between the linked genes?

The first mutant gene reported by $T.H. Morgan$ in $Drosophila$ was the . . . . . . .

Which traits did Morgan choose for the male and female $Drosophila$ respectively to explain linkage and recombination?