The frequency of certain genes in a population changes over generations. This is the essence of the idea of evolution.

$A$ child who inherits an $X-$chromosome from her father will be a boy.

$A$ pea plant with blue colour flower denoted by $BB$ is cross-bred with a pea plant with white flower denoted by $ww$.
$(a)$ What is the expected colour of the flowers in their $F_{1}$ progeny?
$(b)$ What will be the percentage of plants bearing white flower in $F_{2}$ generation,when the flowers of $F_{1}$ plants were selfed?
$(c)$ State the expected ratio of the genotypes $BB$ and $Bw$ in the $F_{2}$ progeny.

New species may be formed if
$(i)$ $DNA$ undergoes significant changes in germ cells
$(ii)$ chromosome number changes in the gamete
$(iii)$ there is no change in the genetic material
$(iv)$ mating does not take place

Give the pair of contrasting traits for the following characters in a pea plant and mention which is dominant and which is recessive:
$(i)$ Yellow seed
$(ii)$ Round seed

$(a)$ Why traits such as intelligence and knowledge cannot be passed on to the next generation?
$(b)$ How can we say that birds are closely related to reptiles and have evolved from them?