Human karyotype , Chromosomes and Genetic information

Scientists discovered that Genetic information which lead to the appearance of traits in all living organisms are carried on the chromosomes & Chromosomes are found inside the nucleus of each cell in all living organisms , At the beginning of the 20 th century .

Genetically , there are two types of cells in all living organisms :

  1. Somatic ( body ) cells : They are produced by mitosis of body cells , which contain homologous pairs of chromosomes , such as cells of skin , muscles , blood , …..and so on .
  2. Sex cells ( gametes ) : They are produced by meiosis of gonads cells ( tests in male and ovary in female ) , They include : Male gametes ( pollens in the plants , sperms in the animals and the humans ) and the female gametes ( ovules in the plants and ova in the animals and the humans ) .


It is the arranging of chromosomes descendingly according to their size , then numerating them , To facilitate the arranging and numerating of chromosomes , they can be coloured with different colours .

We can classify chromosomes when they are in the clearest form , Chromosomes are classified into homologous pairs ( in somatic cells and gonads ) and arranged descendingly according to their size , then they are numerated , This is called the karyotype .

Human karyotype

Human karyotype

The human karyotype :

There are 46 ( 23 pairs ) chromosomes in the human somatic cells , These chromosomes are descendingly arranged in homologous pairs according to their size from number ( 1 ) to number ( 23 ) , where :

The pairs from number ( 1 ) to ( 22 ) are called autosomes or somatic chromosomes , The pair number ( 23 ) represents the sex chromosomes , because it carries the genetic information of sex determination .

The pair of sex chromosomes is characterized by the following :

It does not subject to the arrangement of chromosomes in size because it comes after 7 th pair in size , but it is arranged at the end of chromosomes and given the number ( 23 ) .

It is heterozygous ( asymmetric ) in male ( XY ) and homozygous ( symmetric ) in female ( XX ) , So , the Karyotype of male differs from the karyotype of female .

Numbers of chromosomes

The number of chromosomes in living organisms differs from a species to another , but it is constant in individuals of the same species .

The constancy of chromosomes number in individuals of the same species indicates that chromosomes carry the genetic information that determine the characters of the living organism .

The number of chromosomes in the cells of the living organism does not express its advancement or its size .

Number of chromosomes in somatic and sex cells of living organisms :

Somatic cells

They contain two sets of homologous chromosomes ( one of them is inherited from father and the other from mother ) , They are diploid cells ( 2n ) .

They are produced from mitotic division of cells body , Such as the nucleus of the human somatic cell contain 46 ( 23 pairs ) chromosomes .

Sex cells ( gametes )

They contain half of the chromosomes number that found in the somatic cells , because they are produced by meiosis of gonads cells , they are haploid cells ( n ) .

Such as the nucleus of the human male gamete ( sperm ) and female gamete ( ovum ) contain 23 chromosomes .

Chromosomes and genes :

You are already know that :

Chromosomes are made up of nucleic acid DNA and protein .

DNA is consisted of building units called nucleotides .

DNA molecules carry the genes responsible for the traits of the living organism .

Gene is a sequence of nucleotides on DNA molecule represents a code of a certain protein that is responsible for appearance of a certain trait .

Scientists found that there are 60-80 thousand genes carried on 23 pairs of chromosomes in human , The complex set of genes in the cell is known as the human genome .

Chromosomal theory

You can read this article about Principles of Chromosomal theory & Interpretation of Mendel’s Laws according to chromosomes theory

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