7th Grade Science Student ebook

18.2 VISION

CHAPTER 18: VISION AND HEARING

Color blindness

Not everyone

sees color the

same way

You may be surprised to learn that all people do not see color the

same way. A condition called color blindness affects about 8 percent

of males and 0.4 percent of females. This means that about one out

of every 13 men has color blindness and about one out of every 250

women has color blindness.

Color blindness

is inherited

Although color blindness can be caused by eye disease, it is most

often an inherited condition. More males than females have color

blindness because of how the genes that determine our sex are

inherited. Males have a X and a Y chromosome; females have two X

chromosomes. The color blindness alleles are on the X chromosome

which males receive only from their mothers; they receive the Y

chromosome from their fathers. Because females receive two X

chromosomes, they have two chances to inherit the alleles for

normal color vision.

What is color

blindness?

People who are color blind have trouble seeing certain colors. The

most common condition is red-green color blindness (Figure 18.11).

People with this type of color blindness have trouble seeing reds

and greens. Less common is blue-green color blindness. Complete

color blindness means that the person can only see shades of gray.

Fortunately, this condition is rare.

Living with color

blindness

It is easy to lead a normal life with color blindness. Having color

blindness just means that an individual must look for ways to

adapt to situations where color is involved. For example, color is

extremely important when driving because traffic lights and street

signs are color-coded. Fortunately, in most states, the traffic lights

are vertical and the colors are in the same position—red on top,

yellow in the center, and green on the bottom.

Figure 18.11: This graphic

illustrates how red-green color

blindness affects seeing a traffic light.

The top of the graphic shows what the

traffic light looks like with normal color

vision. The middle and bottom graphic

show what a traffic light looks like with

two of the common forms of color

blindness.