The human species $(Homo\,sapiens)$ have genetic roots in $......$

$A$ trait may be inherited, but may not be expressed. Justify this statement with the help of a suitable example.

$A$ very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.

The number of pair$(s)$ of sex chromosomes in the zygote of humans is

In snails, individuals can change sex, indicating that sex is not genetically determined in them.

$(a)$ How many gene sets should a germ cell have?
$(b)$ Mention two factors causing evolution.