Before we discuss mitosis, let’s testimonial the structure of DNA. Chromosomes room packaged by histone proteins into a condensed structure called chromatin. The an initial level of packaging is represented as the “beads-on-a-string” structure. The condensed dyed is folded and tightly coiled, prefer a coiled call cord, permitting the cell’s DNA to be packed right into the nucleus.

Before a cell can divide, the must very first replicate the DNA so that each the the 2 daughter cell will obtain a complete copy the the DNA. The two identical chromosomes that result from DNA replication are described as sister chromatids. Sisters chromatids are held together by proteins at a an ar of the chromosome called the centromere.

Chromosomes undergo additional compaction in ~ the start of mitosis. When fully condensed, replicated chromosomes show up as special X-shaped structures that are conveniently observed under the microscope (see number below). Chromosomes can have 1 or 2 chromatids, relying on whether they have replicated.

CHROMOSOMAL STRUCTURE

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

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many eukaryotic cell contain 2 sets of chromosomes, with one set originating from the father and also the other from the mother. For example, every person cell has 23 pairs of chromosomes: one chromosome from every pair is inherited from the father (via the sperm), and also the other is inherited native the mother (via the egg).

The figure listed below shows a cell that includes four chromosomes (found as 2 pairs); the pink chromosomes were inherited native the mother and the blue chromosomes were inherited native the father. Each chromosome contributed by the father has actually a matching chromosome the was added by the mother. These equivalent chromosomes, which are alike in structure and also size, constitute a homologous pair (also described as bivalents). The DNA order of homologous chromosomes are usually not specifically identical.

The nuclei the most human cells contain 46 chromosomes. This 46 chromosomes consists 23 pairs of homologous chromosomes, or homologs, an interpretation each of these pairs room alike, yet not have to identical. The 23rd pair that chromosomes in humans determines sex; these two chromosomes might be an extremely different from every other, depending upon gender (XX produce females, XY produce males).


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The convention is to explain the chromosome number in humans as 2n = 46 due to the fact that the cells space diploid, definition they have two finish sets the chromosomes.