Where are genes located?

$........$ is the unit of heredity.

$A$ palaeontologist (a scientist who studies fossils) finds the fossil of an organism in a deeper layer of the Earth. What method will they use to estimate its age?

When a sperm carrying an $X$ chromosome fertilizes an ovum,what will be the sex of the embryo that develops from the zygote?

Study the following cross showing self-pollination in $F_1$ generation,fill in the blank,and answer the question that follows:
Parents: $RRYY \times rryy$
(Round,yellow) (Wrinkled,green)
$F_1$: $RrYy \times$ ?
(Round,yellow)

$A$ child who inherits an $Y$-chromosome from her father will be a girl.