New SAT Reading Practice Test 38: Colorblindness Passage

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Colorblindness Passage

About eight percent of men of European descent
are colorblind, but only about half a percent of
women are affected by the same condition. Most of
these people are "red-green" colorblind, meaning
05they cannot see colors related to green or red. Not
only are they unable to tell red and green apart,
but yellows and oranges do not appear different,
nor do blues and purples. Colorblindness is not
"blindness" but is instead an inability to perceive
10certain wavelengths of light. A red-green colorblind
man looking at a red object can see the object and
can see that it is not white; however, he is unable to
tell whether the object is red or green, as they both
appear similar to him.
15People with normal color vision see color
because they have an array of three types of
photosensitive cells, called cones, on the back of
their retinas. Each type of cone has a different
pigment that is sensitive to a certain part of the
20visible light spectrum. The visible light spectrum
runs from smaller wavelengths at the blue end,
through medium wavelengths in the green to
yellow range, to long wavelengths at the red end.
The cones are often referred to as blue, green,
25and red cones, based on the wavelength of light
they absorb most. The blue cones absorb the blue
wavelengths of light most, although they also
absorb a small amount of the green wavelengths.
The green cones have their maximum absorption in
30the green wavelengths, but also absorb a bit down
into the blue and up into the yellow wavelengths.
The range that the red cones absorb overlaps the
range of the green cones quite a bit; the red cone
maximum absorption is in the yellow wavelengths,
35but red cones also absorb a bit down into the
green, through the yellow, and up into the red
Even though the green and red cones absorb
much of the same part of the visible spectrum, a
40person who lacks the sensitive pigment in either
red or green cones will have difficulty perceiving
either color, because the brain compares the signals
from both to determine exactly which region of
light is being absorbed. With only one set of cones
45sending signals, the brain will perceive light from
the green, yellow, and red wavelengths to be about
the same.
A person will lack the pigment for either green
or red cones if he or she lacks the gene necessary
50to make that pigment. Because genes are inherited
randomly from our parents, half from each parent,
we would expect men and women to have an equal
chance of being colorblind. The actual ratio is
about sixteen colorblind men for each colorblind
55woman. The reason for this inequality becomes
clear once we know that the genes for making the
cone pigments are on the X chromosome.
Women have two X chromosomes, one from
each parent. Men only have one X chromosome,
60which they get from their mother. A woman can
receive a colorblind gene on an X chromosome
from one parent, but if the other X chromosome
has a normal cone pigment gene, she will still make
normal pigments and have normal color vision.
65The woman would need to receive the colorblind
gene from each parent to be colorblind. Since a
man only has the one X chromosome, receiving the
colorblind gene from his mother will always cause
colorblindness in a man.
70Women who have only one copy of the
colorblind gene are referred to as carriers because
they carry the gene but are not affected by it. By
tracking the affected people in a family, we can
create a chart, called a pedigree, to determine
75which women in the family are carriers. A
colorblind daughter must have had a colorblind
father and either a colorblind or carrier mother,
as she must have received a copy of the colorblind
gene from each parent. A colorblind son also must
80have had either a colorblind or carrier mother, but
whether or not the father was colorblind will not
affect the son.

1. The central idea of the passage is primarily concerned with

  • A. how to determine if a person is colorblind.
  • B. research being conducted about colorblindness.
  • C. how people who are colorblind perceive color.
  • D. the genetic and physiological causes of colorblindness.

2. Which choice provides the best support for the answer to the previous question?

  • A. Lines 1-3 ("About eight … condition")
  • B. Lines 15-18 ("People with … retinas")
  • C. Lines 24-26 ("The cones … absorb most")
  • D. Lines 48-50 ("A person … pigment")

3. In paragraph 6, the author includes details about X chromosomes in order to

  • A. give examples of other traits inherited from mothers.
  • B. explain why more men than women are colorblind.
  • C. illustrate how genes affect vision and colorblindness.
  • D. contrast colorblindness with other genetic disorders.

4. Based on the passage, which choice best describes what causes red and green to be the two colors that a colorblind person often cannot perceive?

  • A. A colorblind person is missing both red and green cones on the back of the retinas.
  • B. Because blue wavelengths are brighter, they overpower both red and green wavelengths.
  • C. Because red and green absorption ranges overlap greatly, the colorblind person's brain has trouble interpreting the difference between those two colors.
  • D. Red and green are on opposite sides of the color wheel, so their absorption ranges are at the farthest, opposite ends of the visible light spectrum.

5. Which choice would provide the most support for the author's line of reasoning in paragraph 1?

  • A. Details about other types of colorblindness
  • B. A more detailed explanation of the light spectrum
  • C. A list of other genetic disorders that affect men
  • D. Information about how colorblindness is diagnosed

6. As used in line 19, "sensitive" most nearly means

  • A. delicate.
  • B. responsive.
  • C. sympathetic.
  • D. vulnerable.

7. Based on the information in the passage, it can be reasonably inferred that which of the following statements is true?

  • A. Colorblindness can be corrected with treatments designed to encourage the growth of the missing genes that make pigments.
  • B. A person with normal color vision can become colorblind as he or she ages and the photosensitive cells degenerate.
  • C. A person who is colorblind will experience the visual world in a way that is much different from a person with normal color vision.
  • D. Colorblindness cannot be diagnosed without invasive and expensive genetic testing of both a person and his or her parents.

8. Which choice provides the best evidence for the answer to the previous question?

  • A. Lines 10-14 ("A red-green … him")
  • B. Lines 26-27 ("The blue cones … wavelengths")
  • C. Lines 42-44 ("the brain … absorbed")
  • D. Lines 72-75 ("By tracking … carriers")

9. As used in line 73, "affected" most nearly means

  • A. changed.
  • B. concerned.
  • C. exaggerated.
  • D. involved.

10. Based on the information in the passage and the graphic, which of the following statements is true?

  • A. A male with a colorblind mother and a father who is not colorblind has a 100% chance of being a carrier for the colorblind gene.
  • B. A male with a colorblind father and a mother who is a carrier has a 100% chance of being colorblind.
  • C. A female with a colorblind father and a mother who is not a carrier has a 100% chance of being a carrier for the colorblind gene.
  • D. A female with a mother who is a carrier but not colorblind and a colorblind father has a 100% chance of being colorblind.