Q. Color Blindness and Haemophilia are more common in men than in women..

ANS: Color blindness and Haemophilia are genetic diseases related to "Sex Chromosomes". For understanding the cause, first one must know the Basic of genetics. The following discussion will also contain some notes regarding basic information and finally the answer for the scientific reasons.


CHROMOSOMES:

In humans there are 46 chromosomes in the nucleas of the Cell. Each chromosomes out of 46 has a pair; therefore, there are 23 pair of chromosomes.

SEX CHROMOSOMES:

Out of 23 pair there is one pair of chromosome that is called "Sex Chromosome" pair. Male have "XY" chromosomes as a pair and females have "XX" chromosomes in a pair. The "Y" chromsome in "XY" Chromosome pair in male dummy and only "X" chromosome is functional in the "XY" pair. While in females, one of the "X" is fully functional just like in male, but the other "X" is partially functional.

AUTOSOMES:

Chromosomes other than sex chromosomes are called "AUTOSOMES". Therefore, there are 22 pair of "AUTOSOMES" and 1 pair of "SEX CHROMOSOMES": 22 Autusomes pair + 1 pair of sex chromosomes = total 23 pair of chromosomes

TRAIT:

Any characteristic in human body that is expressed by a single or a group of genes is called trait; for example, eye color, skin color, hair color, etc

GENES:

Each chromosome has several genes located on it. A single Gene is the unit of trait that our body have, for example, the eye color, blood group, etc. It is not necessary that one gene control a single "trait"; for example, there are different genes that control a single trait as Height, Skin color, etc.

Just as a chromosome has a pair, in the say way, every gene has a pair in the other pairing chromosome.


Recessive trait and Dominant Trait

Take an example of eye color; there are various colors of eyes in human, some have black, some have blue, some have hazel, etc. The most common is black. Now consider the situation on genetic level; if in a pair of chromosome, one chromosome has a black eye color gene and the other has blue; then black will be prevalent and expressed in a human body. Therefore, the blue color is recessive and the black is dominant. Blue color of eyes will express itself when there will be both "blue" trait gene in both of pair of chromosomes.


Now, come to the point of HAEMOPHILIA AND COLOR BLINDNESS:

If there happens to be a gene for "Color blindness" (that is "Recessive" in its nature like my above example for blue eyes color) in X choromosome in male as well as in female. Due to lack of one "X" chromosome in male "XY" sex chromosome, the recessive trait of "Color blindness" will express itself. However, in case of females, there are two "XX" chromsomes and one is partially functional, therefore, if a female have a "Color Blindness" trait on one "X" and absent in the other "X", then the female will not suffer from "Colorblindness "; to be "color-blind" the female needed to have "color-blind" gene on both of the pair of sex chromosomes.

Therefore, due to lack of one "X" chromosome in male it is more prevalent or common in male, while in female both "XX" chromosomes decrease the prevalance of the "Color blindness".


What is a color blind carrier?

ANS: When a female has has one colorblind gene in one chromosomes in a pair of gene while the other chromosome is normal; then the female is said to be "Carrier" however, she is not diseased with "Colorblindness".



Diagramatic Expression:
======================

C = chromosome containing color blind Gene
X = Normal Chromosome

(A) WHEN A COLOR BLIND FEMALE MARRIES WITH A COLOR BLIND MALE
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Color Blind Male (CY) Color Blind Female (CX)



. .
. .
. .
. .
. .

CC , CX , CY , XY


CC = Color blind Female

CX = Carrier Female

YC = Color Blind Male

XY = Normal Male


(B) WHEN A COLOR BLIND MAN MARRIES WITH A NORMAL FEMALE
----------------------------------------------------------


Color Blind Male (CY) Normal Female (XX)

. .

. .

. .

. .

CX, CX, XY, XY

CX = Color blind female

CX = Color Blind female

XY= Normal male

XY = Normal male

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