A3.1.9 Diversity of eukaryote genomes Notes

Variation in Eukaryotic Genome Size and Sequence

1. All eukaryotes share the universal genetic code, but their genomes vary greatly in total size and base sequence composition.
2. Variation between species is far greater than variation within a species.

Variation in Eukaryotic Genomes

1. The genome of an organism is its complete set of DNA, including all coding (genes) and non-coding sequences.
2. In eukaryotes, this includes:
   1. Nuclear DNA
   2. Mitochondrial DNA
   3. Chloroplast DNA (in plants)

Why Genomes Differ

1. Differences in eukaryotic genomes arise from two main factors:
   1. Variation in total DNA content (genome size)
      1. Larger genomes contain more non-coding DNA, such as introns and repetitive sequences.
      2. These regions contribute to genome size but not necessarily to gene number.
   2. Variation in base sequence composition
      1. Differences in nucleotide order accumulate through mutation, gene duplication, and deletion over evolutionary time.
      2. These sequence differences explain genetic diversity both within and between species.

Variation in Genome Size

1. Genome size is measured in base pairs (bp).
2. Among eukaryotes, genome size varies by hundreds of thousands of times, mostly due to non-coding regions rather than differences in gene count.

Variation in Base Sequence

1. Within a species
   1. Most individuals share nearly identical base sequences.
   2. Minor differences, such as single nucleotide polymorphisms (SNPs), create genetic variation between individuals.
2. Between species
   1. Base sequence differences are far greater, reflecting long-term evolutionary divergence and independent ancestry.