Color Blind Chart

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Color Blindness & Baldness In People

Color Blindness In Humans: An X-Linked Trait

Pattern Baldness In Humans: Sex Influenced

1. Color Blindness In Humans: An X-Linked Trait

Note: This Is Sometimes Called A Sex-linked Trait

Most nonprimate mammals exhibit dichromacy, with color vision based on just two kinds of visual pigments. These animals do not have full color vision. Although the mechanism of gene inactivation is slightly different in Old and New World primates, the evolution of trichromacy enabled these mammals to see a technicolor world of flowers, fruits and insects. This is somewhat analogous to the evolution of high resolution color monitors from the drab monochrome green and amber progenitors. One obvious advantage of trichromacy is being able to clearly distinguish the subtle shades of ripening fruit from surrounding vegetation. Color vision in higher primates is similar to the the mixing of red, green and blue pixels to generate a full spectrum of color in computer monitors. The following table shows 216 color combinations produced from three colors using a six character hexadecimal HTML code. People with color blindness would have difficulties in distinguishing all of these shades of color.

Different Colors Produced By 6 Character HTML Hexadecimal Code
216 Color Combinations From 000000 (black) to ffffff (white)

000000

000033

000066

000099

0000cc

0000ff

006600

006633

006666

006699

0066cc

0066ff

00cc00

00cc33

00cc66

00cc99

00cccc

00ccff

003300

003333

003366

003399

0033cc

0033ff

009900

009933

009966

009999

0099cc

0099ff

00ff00

00ff33

00ff66

00ff99

00ffcc

00ffff

330000

330033

330066

330099

3300cc

3300ff

336600

336633

336666

336699

3366cc

3366ff

33cc00

33cc33

33cc66

33cc99

33cccc

33ccff

333300

333333

333366

333399

3333cc

3333ff

339900

339933

339966

339999

3399cc

3399ff

33ff00

33ff33

33ff66

33ff99

33ffcc

33ffff

660000

660033

660066

660099

6600cc

6600ff

666600

666633

666666

666699

6666cc

6666ff

66cc00

66cc33

66cc66

66cc99

66cccc

66ccff

663300

663333

663366

663399

6633cc

6633ff

669900

669933

669966

669999

6699cc

6699ff

66ff00

66ff33

66ff66

66ff99

66ffcc

66ffff

990000

990033

990066

990099

9900cc

9900ff

996600

996633

996666

996699

9966cc

9966ff

99cc00

99cc33

99cc66

99cc99

99cccc

99ccff

993300

993333

993366

993399

9933cc

9933ff

999900

999933

999966

999999

9999cc

9999ff

99ff00

99ff33

99ff66

99ff99

99ffcc

99ffff

cc0000

cc0033

cc0066

cc0099

cc00cc

cc00ff

cc6600

cc6633

cc6666

cc6699

cc66cc

cc66ff

cccc00

cccc33

cccc66

cccc99

cccccc

ccccff

cc3300

cc3333

cc3366

cc3399

cc33cc

cc33ff

cc9900

cc9933

cc9966

cc9999

cc99cc

cc99ff

ccff00

ccff33

ccff66

ccff99

ccffcc

ccffff

ff0000

ff0033

ff0066

ff0099

ff00cc

ff00ff

ff6600

ff6633

ff6666

ff6699

ff66cc

ff66ff

ffcc00

ffcc33

ffcc66

ffcc99

ffcccc

ffccff

ff3300

ff3333

ff3366

ff3399

ff33cc

ff33ff

ff9900

ff9933

ff9966

ff9999

ff99cc

ff99ff

ffff00

ffff33

ffff66

ffff99

ffffcc

ffffff

Color blindness or the inability to differentiate between certain color variations is more common in men because they have only one X chromosome. If defective M and L pigment genes reside on their single X chromosome, men will exhibit this trait. Women have two X chromosomes and therefore can be homozygous or heterozygous for the color blind trait. The phenomenon of X inactivation complicates the expression of color blindness in heterozygous females since only one X is functional and the other remains inactive as a Barr body. The inactivation of X chromosomes appears to be a random event.

Test Yourself With The Table Below

Numbers That You Should See If You Are In One Of The Following
Four Categories: [Some Letter Choices Show No Visible Numbers]

	4 Sex-Linked Traits:
	1. Normal Color Vision: A: 29, B: 45, C: --, D: 26
	2. Red-Green Color-Blind: A: 70, B: --, C: 5, D: --
	3. Red Color-blind: A: 70, B: --, C: 5, D: 6
	4. Green Color-Blind: A: 70, B: --, C: 5, D: 2

See Chart of 216 Colors In HTML Code

Note: These Colors May Appear Slightly Different If You Are Red-Green Color Blind

Inheritance Of Color Blindness In Men & Women

Sex-Linked Genes Located On X Chromosome:

+ = Normal Vision (Dominant)
o = Color Blindness (Recessive)

Sex	Color-blind	Normal Vision
Male	X^oY	X⁺Y
Female	X^oX^o	X⁺X⁺ X⁺X^o

Cross Between A Color-blind Man (X^oY) and
Heterozygous Normal Vision Woman (X⁺X^o)

Gametes	X^o	Y^o
X⁺	X⁺X^o	X⁺Y
X^o	X^oX^o	X^oY

In the above cross, four different possible offspring are produced:

X^oY: Color-blind Boy (1/4 or 25%)

X⁺Y Normal Vision Boy (1/4 or 25%)

X^oX^o Color-blind Girl (1/4 or 25%)

X⁺X^o Heterozygous Normal Vision Girl (1/4 or 25%)

Note: The heterozygous normal vision girl carries the recessive gene for
color blindness. On the average, she will pass this gene on to half of her
sons and half of her daughters.

Frequency Of Normal & Color-blind Genes In A Population

The men's sperm carry one of the following three combinations: An X chromosome with the gene for normal vision (X⁺), an X chromosome with the gene for color-blindness (X^o), or a Y chromosome (Y). The women's eggs carry one of the following two combinations: an X chromosome with the gene for normal vision (X⁺), or an X chromosome with the gene for color blindness (X^o). She does not carry the Y chromosome (Y) in her eggs.

Gametes of
the Men &
Women in
Population

Decimal
Value
of the
Gametes

Sperm

X⁺
0.450

X^o
0.050

  Y^o
0.500

Eggs

X⁺
0.900

X⁺X⁺
0.405

X⁺X^o
0.045

X⁺Y
0.450

X^o
0.100

X⁺X^o
0.045

X^oX^o
0.005

X^oY
0.050

Assuming that the X and Y-bearing sperm are produced in an equal ratio, then 50% (0.5) of the sperm carry the Y chromosome and 50% (0.5) of the sperm carry the X chromosome. Since a small percentage of the X-bearing sperm carry the recessive color-blind gene, their numerical value is 5% (0.05). The majority of X-bearing sperm carry the dominant allele for normal vision and their numerical value is 45% (0.45). 90% (0.9) of the X-bearing eggs carry the dominant allele for normal vision, and 10% (0.1) of the eggs carry the recessive allele for color blindness. It is necessary to include these small proportions of sperm and eggs that carry color-blind alleles in order to account for the percentages of color-blind males and females in the population.
Based upon the gene frequencies of the parents in the population, all of the genotype percentages can easily be calculated by multiplying the decimal values of different sperm and eggs together. For example, 0.5% (0.005) of the population are colorblind females X^oX^o (0.05 x 0.10 = 0.005). Five percent (0.05) of the population are color-blind males X^oY (0.5 x 0.1 = 0.05). This is roughly equivalent to the percentages of color-blind females and males in the U.S. population.

For More Information, See Exercise 4 in Biology 100 Lab Manual:

Armstrong, W.P. 1988. Biology Laboratory Manual & Workbook
     Burgess International Group, Inc., Edina, Minnesota.

2. Pattern Baldness In Humans: A Sex Influenced Trait

Pattern baldness in men is a sex-influenced trait. It is not an X-linked trait like color blindness and hemophilia. Baldness is an autosomal trait and is apparently influenced by sex hormones after people reach 30 years of age or older. This condition is inherited as a simple Mendelian trait, although the biochemical mechanism is complex. There are other causes for baldness not related to simple Mendelian genetics, such as illness, severe stress, and pulling one's hair out by the roots. In men the gene is dominant, while in women it is recessive. A man needs only one allele (B) for the baldness trait to be expressed, while a bald woman must be homozygous for the trait (BB). Since a bald woman must inherit the baldness trait from her mother and father, it is less common in females. In addition, the trait typically results in women with thinning hair rather than completely bald. The gene is readily passed from mother to son because he will inherit one set of her chromosomes.
If B is the allele for baldness and b is the allele for normal hair, a bald man can be heterozygous (Bb) or homozygous bald (BB). A man with normal hair must be homozygous normal (bb). A normal woman can be homozygous normal (bb) or heterozygous (Bb). A woman who has thinning hair and a receeding hair line in later life must be homozygous bald (BB).

Sex

      Baldness

    Normal Hair

Male

BB, Bb

bb

   Female

BB

Bb, bb

If you are a man with a bald father, you are doomed to lose your hair if your father is homozygous bald (BB). If he is heterozygous (Bb), you have a 50-50 chance of inheriting his gene for normal hair (b). If you also inherit the gene for normal hair from your mother, then your genotype will be bb and your phenotype will be normal hair:

   Gametes

Sperm
B                          b

              b
  Eggs
              b
          Bb

          bb

Bb

bb

If your grandfather on the mother's side of your family is bald, then you have a 50-50 chance of inheriting this gene from your mother:

   Gametes

Sperm
b                          b

              B
  Eggs
              b
          Bb

          Bb

bb

bb

If your grandfather on the mother's side of your family is bald and your father is heterozygous bald, then you have a 75% chance of losing your hair:

   Gametes

Sperm
B                          b

              B
  Eggs
              b
          Bb

          Bb

Bb

bb

If your grandfather on the mother's side of your family is bald and your father is homozygous bald, then you have a 100% chance of losing your hair:

   Gametes

Sperm
B                          B

              B
  Eggs
              b
          BB

          BB

Bb

Bb

Baldness Thinking Question
A photo album clearly shows that both of your grandfathers were bald, but there is no other evidence of baldness in your family. What is the fractional probability that you will lose your hair? Note: This question involves that probability that your mother carries the baldness gene, and the chance that you will also inherit the gene for baldness.

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