For the preparation of genetic maps,the recombination frequencies between genes are additive over short distances but not over long distances due to

$A$ cross is made between two homozygous individuals, one with the wild type $(+, +)$ and the other with the mutant type $(a, b)$. In the $F_2$ generation (or test cross progeny), out of $1000$ individuals, $700$ are parental types. Calculate the distance between genes $a$ and $b$.

Mendel observed that some traits do not assort independently. Later research showed that this is due to .....

Genetic variation is observed in sexually reproducing species.

Select the incorrect statement$(s)$ from the options given below with respect to dihybrid cross.
$I.$ Tightly linked genes on the same chromosome show higher recombinations.
$II.$ Genes far apart on the same chromosome show very few recombinations.
$III.$ Genes loosely linked on the same chromosome show similar recombinations.

Crossing over in a diploid organism is responsible for