The haploid number of chromosomes for dogs is 39 How many TO

The haploid number of chromosomes for dogs is 39. How many TOTAL chromatids would be found in a normal somatic cell from a dog?

Solution

Ans. A chromosome and its duplicated copy (formed during S-phase of cell division) are called sister chromatid of each other; and form a chromatid-pair when together. A sister- chromatid pair separates into two independent chromosomes during anaphase.

A chromatid is equivalent to one chromosome. Or, both the terms represent the condensed form of a single linear DNA but named differently depending on the stage of cell cycle..

Now,

Total number of chromosomes in normal somatic cell = 2 n            ; [n = haploid number]

                                    = 2 x (39) = 78

It is noteworthy that the term “chromatid” is restricted for “the condensed form of DNA during M-phase of cell division - as long as two sister chromatids are connected to each other”. In all placed except this, the term chromosome is used to represent the condensed form of DNA. That is, technically, a normal somatic cell does not have its DNA in form of chromatid, it’s in form of chromosome only.

For the time being, it’s assumed that “chromatid” represents a “chromosome”.

So, number of chromatids in normal somatic cell = 78