4.1: DNA, Genes, and Chromosomes
Each DNA nucleotide is composed of a 5 carbon sugar (deoxyribose), a phosphate group,
and one of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine
(T).
The nitrogenous bases project out from the sugar phosphate backbone of DNA. Double
ringed nitrogenous bases (adenine and guanine) are called purines. Single ringed
nitrogenous bases (thymine and cytosine) are called pyrimidines.
Homologous chromosomes: carry the same genes. They have in common; their length,
centromere location, and banding pattern.
Although homologous chromosomes appear identical, they carry different forms, or
alleles, of the same genes at the same location, or locus (plural loci). On these
chromosomes, the upper-case and the lower-case letters denote different alleles of the
same gene.
Label the diagram.
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