A hammer is a lever, one of the six types of simple machines.
Ans.
Sex-linked genes are those genes that found on sex-chromosomes (X and Y chromosomes) and their phenotypic expression for a trait depends on the gender of the offspring.
Most of the sex-linked genes are present on X chromosomes as X chromosomes have more number of genes as they are made up of more DNA as compared to Y chromosome.
However, male individuals are more likely to exhibit the sex-linked traits. It is because most of the sex-linked traits are recessive and males have only one copy of X chromosome, while females have two copies of X chromosome. One mutated copy in male can exhibit the trait, while in females, both of the mutated copies are required to exhibit that trait.
The people represented by the ends of the bell-curve are the most rare.
This could mean that if it's an iq curve the people at the ends have either a really high or really low iq etc.