DNA, Gene Structure, and DNA Replication - Insect Molecular Genetics - page 16

Table 1.1: The 20 Amino Acids that Occur in Proteins and their Codons.

Amino acid Abbreviation Codons

Alanine ala GCU GCC GCA GCG

Arginine arg AGA AGG

Asparagine asn AAU AAC

Aspartic acid asp GAU GAC

Cysteine cys UGU UGC

Glutamic acid glu GAA GAG

Glutamine gln CAA CAG

Glycine gly GGU GGC GGA GGG

Histidine his CAU CAC

Isoleucine ile AUU AUC AUA

Leucine leu UUA UUG CUU CUC CUA CUG

Lysine lys AAA AAG

Methionine a met AUG

Phenylalanine phe UUU UUC

Proline pro CCU CCC CCA CCG

Serine ser AGU AGC

Threonine thr ACU ACC ACA ACG

Tryptophan a

trp UGG

Tyrosine try UAU UAC

Valine val GUU GUC GUA GUG

a Methionine and tryptophan are underlined because they are specified by only one codon.

eubacterial (operational genes) lineages, indicating that eukaryotic genomes are
chimeric ( Lang et al. 1999, Nesbo et al. 2001 ).

1.12 Gene Organization
All genes are located on chromosomes. Each chromosome contains a single DNA
molecule. These DNA molecules contain hundreds or thousands of genes in
insects. For example, the fruit fly Drosophila melanogaster is estimated to have
≈ 13,600 genes distributed on four chromosomes ( Adams et al. 2000 ). Genes may
be spaced out along the length of a DNA molecule, with DNA sequences inter-
vening that do not code for proteins, or the genes may be grouped into clus-
ters. Genes in a cluster may be related or unrelated to each other in structure
and function. There are segments of DNA in eukaryotes in which the nucleo-
tide sequences apparently do not code for anything; this DNA has been called
“spacer” or intergenic DNA if it occurs between genes. Studies indicate that
these noncoding sequences often are transcribed into RNAs that have gene reg-
ulatory functions.

Multigene families are clusters of related genes with similar nucleotide
sequences. Multigene families may have originated from a single ancestral