Notes, Exercises, Videos, Tests and Things to Remember on Chromosomes
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The thread-like structure which is located inside the nucleus of animal and plants cells are known as chromosomes. The word chromosome is derived from the Greek word 'chromo' which means color and 'soma' which means body. The size of the chromosome varies from one to another species which is visible during the cell division. All the plants and animals have a fixed number of chromosomes in their cells which is always present in pairs.
Structural Features of Chromosomes
The one-half of the chromosome is derived from the mother and the other half is derived from father. The part of the chromosome derived from mother is maternal chromosome and the part of the chromosome derived from father is called parental chromosome. Thus, the homologous chromosome is the chromosome which is formed combinedly from parental and maternal chromosome. Similarly, we can say that a homologous chromosome is those chromosome pairs which is obtained from each parent that have a similar structure, height, gene position, and centromere location. The replicas of a single chromosome held together by a common centromere after DNA replication are known as sister chromatids.
There are 23 pairs of chromosomes in a human body. The one set of a chromosome is obtained from the female parent through egg and the other set of a chromosome is obtained from male parent through sperm. During the process of fertilization, the cell obtained from the fusion of sperm cell and egg cell is known as the zygote, which contains two sets of homologous chromosomes.
Function of Chromosomes
The major role of a chromosome is during the cell division and inheritance of hereditary characters from parents to their offsprings. They help in the growth and metabolic activities.
Diploid and Haploid Cells
Diploid and haploid are two types of cells found in the body of plants and animals. The diploid cells contain two complete sets of a chromosome which is represented by 2n. For example: somatic cells like skin cell, muscle cell , plant cells such as parenchyma cell, reproductive cell, etc.
The haploid cells contain only one complete set of chromosomes which is half the number of chromosomes as comared to diploid cell that is represented by n. For example: spores, male gamete, egg, etc.
The number of chromosomes varies in the cells of diffeent living organisms. Some of them are listed as follows:
|Organisms||Number of Chromosomes|
|Total Number||Number in pairs|
|Mice/ Rat||40||20 pairs|
|Onion (Allium ceipa)||16||8 pairs|
|Pea (Pisum sativum)||14||7 pairs|
|Solanum nigrum||16||8 pairs|
Chromosomes are known as hereditary materials because they transfer the genetic characters from parents to the offsprings from a generation to other generations.
Chromosome: Chromosomes are the genetic substances that help in the inheritance of characters from parents to their offsprings.
Chromonema: The fine greatly coiled thread or filament contained by chromosome is said to be chromonema.
Chromosomes are of five types, on the basis of presence or absence and position of centromere:
Homologous chromosomes are the pair of chromosomes, one from each parent, which are similar in length, gene position and centromere location.
The major role of chromosomes during the cell division is to inheritance of hereditary characters from parents to their offsprings. They also help in growth and metabolism.