Molecular Biology Tutorials

Karyotype and Idiogram: Definition and Importance of Karyotype Test (Karyotyping) in Human


what is karyotyping

(image source: wikipedia)

Karyotype, Karyotyping and Preparation of Idiogram

What is a Karyotype?

All species are characterized by a set of chromosomes to carry their genetic information. The chromosomal composition of each species has a number of characteristics. The Karyotype is a set of characteristics that identifies and describes a particular set of chromosome. These characteristics which are described by a karyotype are:-

(1).  The chromosome number

(2).  Relative size of different chromosomes

(3).  Position of centromere and length of chromosomal arms

(4).  Presence of secondary constrictions and satellites

(5).  Banding pattern of the chromosome

(6).  Features of sex chromosomes

What is Karyotyping? How to Prepare the Karyotype of Human?

Ø  The process of preparation of the karyotype of a species is called Karyotyping.

Ø  Karyotyping is now most commonly used in clinical diagnosis and clinical genetics.

Ø  Karyotype is prepared from the microphotographs of metaphase chromosomes.

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Molecular Biology Tutorials

Classification of Chromosomes based on Position of Centromere and Length of Chromosomal Arms


how chromosomes are classified

Classification of Chromosomes Based on Position of Centromere and Length of Arms

Ø  The size and shape of the chromosomes are variable in the different phases of cell cycle.

Ø  Chromosomes in the interphase of cell appear as thin, coiled, elastic and thread-like structures.

Ø  This thread-like stainable interphase chromosome is called chromatin.

Ø  During the mitotic or meiotic cell division, the chromatin materials become thicker in their width and shorter in their length.

Ø  Chromosomes in the metaphase stage of cell division show maximum condensation.

Ø  Each metaphase chromosome contains a centromere (primary constriction).

Ø  The centromere divides the chromosome into two parts called chromosomal arms.

Ø  The small arm of the chromosome is denoted as ‘p’ – arm, whereas the large arm is denoted as the ‘q’ – arm.

Ø  When chromosomes are represented as a karyotype or ideogram, each chromosome is arranged in such a way that the ‘p’ arm is positioned above the centromere and the q arm is represented below the centromere.

Ø  The position of centromere and the relative size of chromosomal arms are used as a criterion for a morphological classification of chromosomes.

Ø  This morphological classification is an important karyotypic feature of an organism.

Classification of chromosome

Ø  Based on the position of centromere and length of chromosomal arms, the chromosomes are classified into 4 groups:

(1).      Telocentric chromosomes

(2).      Acrocentric chromosomes

(3).      Sub-metacentric chromosomes

(4).      Metacentric chromosomes

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Molecular Biology Tutorials

Cell Cycle Checkpoints in Regulation of Cell Division and Cancer


Cell Cycle Checkpoints and Cancer

Cell Cycle Checkpoints and Regulation of Cell Cycle

What is cell cycle checkpoint?

Every cell in our body pass through a series of different stages in a cyclic manner called cell cycle.  Cell cycle is a sequential step that taking place in a cell leading to the accurate duplication of genetic materials (DNA), precise separation of replicated genetic materials and passing them in to two daughter cells.  The process of cell cycle is very critical in each cell, thus it operate strictly under strong surveillance to prevent any mistakes. This strong surveillance system in the cell to monitor the cell cycle progression itself is called cell cycle checkpoints.

Checkpoints are surveillance mechanisms that halt the progress of cell cycle if (1) any of the chromosomal DNA is damaged, or (2) critical cellular processes, such as DNA replication during S phase or chromosome alignment during M phase, have not been properly completed. Thus cell cycle checkpoints ensure that the various events in the cell cycle progression occur accurately and in correct order. In this post we will discuss the three types of cell cycle checkpoints that operate in eukaryotic cells during cell cycle progression.

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