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                                            nucleus             Pairs of chromosomes are found

                                                                 in the nucleus of a cell. One
                                                                  chromosome from each pair is
                                                                    inherited from each parent.



                                 chromosome                            gene
                                                                        gene

                                                                                  Cytosine
                                                                                   cytosine
                                                                                               Adenine
                                                                                                adenine
        Chromosomes are made up
        of DNA (deoxyribonucleic acid),
                                                                                         C
        the hereditary material in humans                DNA
        and most other organisms.                       DNA                           G      A
                                                                                           T
        The hereditary information in DNA is
                                                                   Guanine
        stored as a code of four nitrogen bases:                  guanine
        Adenine, Guanine, Cytosine, and Thymine.
                                                                                 Thymine
                                                                                thymine
        What is a Gene?                                                        Human Karyotype                           100,000 genes


        Specific sections of the DNA are called genes. Each
        gene provides the cell with different information.


        Each chromosome is made up of many genes.                        1     2      3                  4     5
        There are about 100,000 genes found on human
        chromosomes.
                                                                         6     7      8     9     10     11    12
                               chromosome

                                                                        13     14     15          16     17    18
                           gene                                                                           or

                                                                        19     20       21    22
                                         gene                                                      XX (female)  XY (male)

                                                                       In each human body cell, there are 46
                                                                       chromosomes, existing in 23 pairs.

                 DNA
                strand







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