CHROMOSOMES

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Chromosomes In a General term are rod or thread like bodies found in the nucleus of a cell.
Chromosome houses or contains the genes which are responsible for the transmission of characters from parents to offspring.
Chromosomes can be seen with a microscope only during cell division (mitosis or meiosis). They appear at the beginning of cell division as long slender threads. As cell division progresses, they shorten and thicken. After some time, each chromosome is observed to be made up of two threads called chromatids, held together at the centromere.

IMAGE SOURCE: http://biology4alevel.blogspot.com/2014/09/29-dna-structure.html

Number of Chromosomes
The number of Chromosomes in a body cell known as the diploid number is double the number of Chromosomes in a gamete known as the haploid number. Diploid number is represented by 2n while Haploid number is represented by n. Example of Chromosomes number in body cells are: Cat 38 (19 pairs), housefly 12 (6 pairs), domestic fowl 18 (9 pairs), dog 52 (26 pairs), Man 46 (23 pairs).
There are naturally 46 Chromosomes which occur as 23 pairs in Human Beings. Easy Chromosomes of a pair occupies the same position as and is similar in shape and size to the other while each of the pair is called homologous chromosomes and only separate during meiosis. Chromosomes are numbered in multiple of 23 which is represented as n I.e 23 = n.
Therefore, the 46 chromosomes are represented as 2n, I.e. 2 × n = 2 × 23 = 46. Since 46 chromosomes is twice n, it is called the diploid number of Chromosomes while n (23) is called the haploid number.

PROCESSES IN WHICH HEREDITARY CHARACTERISTICS ARE BEING TRANSMITTED BY CHROMOSOMES

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• The chromosomes carry the genes, pass into the gamete during meiosis.
• During the first stage of meiosis, the homologous chromosomes separate into two daughter cells.
• In the second stage of meiosis, the two chromatids in each chromosome separate. This process brings about the segregation of genes. Each gamete therefore can only contain one gene for one of a pair of contrasting characteristics.
• During fertilisation, the gametes fuse together. The zygote receives two genes for the same character- one from one chromosome in the egg from the female parent and the other from one chromosome in the sperm from the male parent.
• In cases where two genes are the same, the offspring is homozygous but when they are different, the offspring is a hybrid (heterozygous) with respect to that character.
• A gene in a chromosome dictates the formation of a protein, usually an enzyme which affects the formation of cell products that bring about the expression of a character.

REFERENCES

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http://projects.cbe.ab.ca/Diefenbaker/Biology/Bio%20Website%20Final/notes/molecular_genetics/5_structure_chromosomes.htm

https://ghr.nlm.nih.gov/primer/basics/chromosome

https://www.britannica.com/science/chromosome

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