Freckles
Freckles have dominant predisposition (F). A dad who has F/F (he has freckles) and a mom who has f/f will have kids with freckles. Making a cross scheme, we see 4 pieces of F/F.Examples: if both mom and dad have f/F, 3 out of 4 kids will get freckles while fourth child will not get freckles. In a cross scheme, we see that there is a 75% chance that their child will get freckles.
Propensity
A predisposition can be due to several genes and then there can be many variations of colors, not just black or white. Environment also plays a role. In the skin there are many colors and the sun, for example, gives some people more melanin and the skin becomes darker.
Gender-linked inheritance
Damage in the X sex chromosome causes hemophilia. Girls have two X chromosomes, which means there will always be a healthy chromosome. But guys have XY chromosomes and if X is damaged then the boy gets hemophilia. Therefore, almost never girls are the ones affected.
Color blindness
Color blindness sits in the Y chromosome, therefore girls never become color blind.Genes are influenced by both inheritance and environment. Allergy and type 1 diabetes are examples of environmental influences.
