What does the given symbol represent in a pedigree chart?

If a colour blind lady marries a normal man,their children will be:

Which of the following is a sex-linked disease?

$A$ woman with normal vision marries a man with normal vision and gives birth to a color-blind son. Her husband dies,and she remarries a color-blind man. What is the probability of color blindness in her children from the second marriage?

In a cross between a male and female, both heterozygous for sickle cell anaemia gene, what percentage of the progeny will be diseased? (In $ \%$ )

Which one of the following is a dominant trait?