On which of the following plant species has Mendel worked?

What are fossils? How are they formed? Describe in brief two methods of determining the age of fossils. State any one role of fossils in the study of the process of evolution.

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

$(a)$ "Chromosomes are heredity carriers." Why do we say so?
$(b)$ Which vital function is not controlled by autosomes?

"The chromosome number of the sexually reproducing parents and their offspring is the same." Justify this statement.

$(a)$ Which type of organs are shown in the figure below?
$(b)$ What is the origin and structure of these organs?