D2.1.9 Meiosis as a reduction division

Apuntes

• Subtopic: Chromosomes and Genes The nucleus of a cell contains the chromosomes. Each chromosome is a very long DNA molecule with some associated proteins. Along a chromosome is a sequence of genes. An average human chromosome has about a thousand genes in a linear sequence. When the DNA in a chromosome is replicated, the gene sequence does not change. This means the sequence of genes shows continuity through the generations in a species, potentially over millions of years. There are major disadvantages to changes in gene sequence, and such changes are only common during the evolution of new species. Chromosomes with the same sequence of genes as each other are homologous. Although the sequence of genes on a chromosome is resistant to change, the base sequence of individual genes on a chromosome can change by mutation, resulting in new alleles. These alleles can be reshuffled during meiosis to produce new combinations. This process is called recombination, and together with gene mutation, it explains how chromosomes can be homologous but not identical. • Subtopic: Haploid and Diploid Numbers A species has a characteristic number of types of homologous chromosomes. This is kn...