17.1 Chromosomes, genes and proteins

Chromosomes are DNA molecules. A gene is a length of DNA that codes for a protein. An allele is an alternative form of a gene. Inheritance of sex via X and Y chromosomes (XX female, XY male). HL extension: base sequence in a gene determines amino acid sequence in the protein, which determines shape and therefore function. Protein synthesis flow — gene stays in nucleus, mRNA copies the gene, exits to cytoplasm, ribosome assembles amino acids into the protein. Selective gene expression. Haploid vs diploid nuclei — humans are diploid (46 = 23 pairs) in body cells; gametes are haploid (23).