Chromosomes
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Chromosomes are found in the nucleus of all cells in the body. They contain the genetic material that determines an organism’s characteristics.
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Each chromosome is composed of a long strand of DNA wrapped around proteins.
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Human cells have 23 pairs of chromosomes, totalling 46.
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During cell division, chromosomes duplicate, resulting in two identical sets which are separated into the two new cells.
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Chromatin, a substance found in the nucleus, condenses to form chromosomes when cells divide.
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Chromosomes are visible under a microscope during cell division.
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Each chromosome carries genes, and different genes have different locations on the chromosome. These locations are known as loci (singular: locus).
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The two chromosomes in a pair (homologous chromosomes) carry the same kinds of genes in the same locations, but the specific versions (or alleles) of those genes might be different.
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Sex determination in humans is linked to a specific pair of chromosomes, named the X and Y chromosomes.
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Cells in our bodies (somatic cells) have two sets of chromosomes and are termed diploid, while sex cells or gametes (sperm and eggs) have one set of chromosomes and are termed haploid.
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Errors in the distribution of chromosomes during cell division can result in genetic disorders. For example, Down Syndrome is caused by an extra copy of chromosome 21.
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The study of chromosomes, their structure, functions, and their role in heredity is called cytogenetics.