What does this diagram indicate?

In a monohybrid cross,if you get a $3:1$ ratio,it denotes that:

In garden pea,round shape of seeds is dominant over wrinkled shape. $A$ pea plant heterozygous for round shape of seed is selfed and $1600$ seeds produced during the cross are subsequently germinated. How many seedlings would have the parental phenotype?

$A$ man homozygous for brown eye colour marries a lady heterozygous for brown eye colour. Brown eye colour is dominant over blue. What will be the phenotype of their children?

In Mendel's monohybrid cross experiment,what was the percentage of heterozygous genotypes in the $F_2$ generation?

When the $F_1$ hybrid $Tt$ is crossed with the recessive parent $tt$,it is a case of....