Jumat, 14 Maret 2014

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Color Blindness, Hemophilia, Brown Teeth, Drosophila Melanogaster - Linkage

Linkage sex linkage is the genes that are set in sex chromosome. consequently, there are two types of sex linkage, X linkage and Y linkage. X linkage are the genes that are only found in X sex chromosome. The examples are the genes causing color blindness, hemophilia, and brown teeth. Y linkage are the genes that are only found in Y sex chromosome. The example are the genes causing webbed fingers, hypertricosis, and hystrix gravior.

Next, we will discuss several cases of sex linkage, such as color blindness, hemophilia, brown teeth, and red eye in fruit fly.

Color Blindness

Color blindness. A person that does not have color blindness can easity notice the number in the above color  combination

A detail report on color blindness case was first written by a British Chemist that had color blindness, John Dalton. There are two types of color blindness, total color blindness and partial color blindness. Total color blindness (achromatopsia monochromatism) is caused by recessive genes reside in X and Y chromosome; therefore, the percentage of total color blindness patient between male and that of female is the same. A person suffering from total color blindness is unable to differentiate all light colors. The color that can be seen is only grey.

The example of marriage result possibilities between a color blindness carrier woman and a normal man

Partial color blindness (dischromatism) is an eye disorder by which The patient is unable to differentiate between red and green or blue and yellow. The disorder is caused by X linkage recessive gene. The color blindness case often occurs on approximately 7% male and 1% female.




Hemophilia started to be investigated and studied profoundly since the death of Prince Alfonso (Spain) due to an accident. In the accident, the prince run out of blood even though the wound was not severe. Nowadays, it is known that there are two types of hemophilia, which are as follows.

  1. Hemophilia A is caused by the disability of the body in forming VIII factor or AHF ( antihemophilia factor).
  2. Hemophilia B or Christmas disease is caused by the disability of the body in forming IX factor or tromboplastin plasma component (TPC).
The exampte of marriage result possibitities between a hemophilia carrier woman and a hemophitia man

Similar to color blindness case, hemophilia is also caused by X linkage recessive gene (h). The heredity pattern is also similar to color blindness case.

Brown Teeth

The exampte of result possibitities from a marriage between a brown tooth woman and a normal tooth man

Brown teeth case is a genetic disorder caused by a defect in the formation of email layer on teeth. Since the email is not formed, teeth become brown and easily damaged. The disorder is caused by X linkage dominant B gene.

Drosophila Melanogaster

The gene that determines the formation of eye color in fruit fly (Drosophila melanogaster) is X linkage gene. The gene that determines Red color eye is dominant to the one determining white color eye. Look at The following Figure
The exampte of result possibitities in the cross between a homozygous red eye female fruit fly and a white eye mate fruit fly and the cross between F1

Source: Source: Essential Biology, 2006.

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