Before we talk about mitosis, let’s review the framework of DNA. Chromosomes are packaged by histone proteins right into a condensed structure called chromatin. The very first level of packaging is stood for as the “beads-on-a-string” structure. The condensed dyed is folded and tightly coiled, favor a coiled phone call cord, permitting the cell’s DNA to it is in packed right into the nucleus.

Before a cell have the right to divide, that must very first replicate the DNA so that each the the two daughter cell will get a complete copy of the DNA. The two identical chromosomes that result from DNA replication are described as sister chromatids. Sister chromatids are hosted together by protein at a an ar of the chromosome referred to as the centromere.

Chromosomes undergo added compaction in ~ the start of mitosis. When fully condensed, replicated chromosomes show up as special X-shaped frameworks that are readily observed under the microscopic lense (see figure below). Chromosomes can have 1 or 2 chromatids, depending upon whether they have replicated.

CHROMOSOMAL STRUCTURE

A chromatid is a condensed DNA subunit that a chromosome. The 2 chromatids the a copied chromosome are organized together at a region of DNA dubbed the centromere (see number below). Centromeres room the attachments points for microtubules, which space responsible for the guiding the movement of chromosomes throughout mitosis and also meiosis.

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many eukaryotic cell contain two sets that chromosomes, through one collection originating indigenous the father and the other from the mother. For example, every human being cell has actually 23 pairs of chromosomes: one chromosome from each pair is inherited from the dad (via the sperm), and the various other is inherited indigenous the mother (via the egg).

The figure listed below shows a cell that includes four chromosomes (found as two pairs); the pink chromosomes to be inherited indigenous the mother and also the blue chromosomes were inherited indigenous the father. Each chromosome contributed by the father has actually a equivalent chromosome that was contributed by the mother. These corresponding chromosomes, which are alike in structure and size, constitute a homologous pair (also referred to as bivalents). The DNA order of homologous chromosomes room usually not specifically identical.

The nuclei that most human cells save on computer 46 chromosomes. These 46 chromosomes consists 23 bag of homologous chromosomes, or homologs, meaning each of these pairs room alike, however not have to identical. The 23rd pair that chromosomes in human beings determines sex; these two chromosomes might be an extremely different from every other, relying on gender (XX to produce females, XY produces males).


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The convention is to describe the chromosome number in human beings as 2n = 46 due to the fact that the cells room diploid, meaning they have actually two complete sets the chromosomes.