The human body is made up of billions of cell of different sorts that form the building blocks for all the tissues and organs. Each cell is given specific instructions on how to grow, function and develop by a specific code called DNA (deoxyribonucleic acid) which is our genetic material.
These instructions come in discrete units called genes. Chromosomes are the material in which the genetic material is packaged.
Most cells in the human body have 46 chromosomes which come in 23 matching pairs. One chromosome in each cell is inherited from each of our parents. Of the 23 pairs, 22 are autosomes and 1 pair of sex chromosomes. It is the sex chromosome that determines the gender of any human. A female has 2 X chromosomes and a male 1 each of X and Y. The entire X chromosome in a human male is active but this is not the case in a female where one of her X chromosomes is by and large inactive.
All traits in human beings are determined by the genes on their chromosomes. Sex-linked chromosomes can be distinguished by their manner of transmission through successive generations of a family.
Recessive diseases occur when a person has a duplicate copy of a bad gene. Hence X-linked recessive disorders are more likely to occur with women than men as women have two copies of the X chromosome.
Women who are carriers of a recessive disease pass the recessive gene down through generations. Generally, as in the case of color blindness, a disease transmitted through a mutant gene of the X chromosome, about half her male offspring are affected whereas half her daughters become carriers but themselves remain unaffected. Other well known diseases which behave similarly are hemophilia and Duchenne muscular dystrophy.
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