Ch 9 Evolution of Genes & Genomes -revised

Chapter 9: How Genes and Genomes Evolve

Germ-Line and Somatic Cells

  • Functions:

    • Germ-line cells propagate genetic information to the next generation.

    • Somatic cells do not pass genetic information to progeny.

Mutations in Germ-Line and Somatic Cells

  • Consequences of Mutations:

    • Germ-line mutations are inherited by offspring.

    • Somatic mutations affect only the individual (not passed on).

Mechanisms of Genome Alteration

  • Genome Alterations:

    1. Caused by failures in DNA replication or maintenance.

    2. Genetic changes that contribute to evolution include:

      • Point mutations

      • Insertions/Deletions

      • Gene duplications

      • Chromosomal rearrangements

      • Horizontal gene transfer

      • Transposable elements.

Point Mutations and Regulatory Changes

  • Impact of Point Mutations:

    • Mutations in coding regions are noticeable.

    • Mutations in regulatory regions can be subtle but have significant effects, such as affecting disease resistance.

    • Example: A mutation in a receptor prevents malaria infection.

Lactase Persistence and Gene Mutation

  • Lactase and Domestication:

    • Evolution of lactase expression in humans correlates with cattle domestication about 10,000 years ago.

    • Two independent mutations allow adult lactose digestion; prevalent in Northern Europe and Central Africa.

Changes in Regulatory DNA

  • Evolution of Regulatory Sequences:

    • Changes in regulatory DNA can influence gene expression and organismal development across embryonic stages.

Gene Duplication and Functional Divergence

  • Mechanisms of Gene Duplication:

    • Gene duplication allows one copy to mutate and develop new functions.

    • Occurs through unequal crossing-over during meiosis, creating gene families.

Evolution of the Globin Gene Family

  • Globin Gene-Mutation Dynamics:

    • The globin family originated from a single-chain globin molecule leading to the current four-chain hemoglobin.

    • Not all duplications yield new functional genes; many are pseudogenes.

Whole Genomic Duplications

  • Occurrence of Genome Duplications:

    • Whole genome duplications are rare but significant in evolution, like those observed in Xenopus species.

Exon Duplications and Shuffling

  • Exon Duplication:

    • Exons can be duplicated, and their combinations can lead to novel proteins.

  • Exon Shuffling:

    • Transposable elements facilitate varied exon arrangements which enhance protein diversity.

Horizontal Gene Transfer in Bacteria

  • Conjugation in Bacteria:

    • Bacterial cells can exchange genetic material through conjugation, affecting traits like antibiotic resistance.

Phylogenetics and Evolutionary Relationships

  • Phylogenetic Trees:

    • Show evolutionary relationships based on nucleotide sequences; humans are closer to chimpanzees than gorillas.

Ancestral Gene Reconstruction

  • Gene Sequence Comparison:

    • Analyzing closely related species allows the reconstruction of ancestral genes, exemplified by the leptin gene sequences in humans and chimpanzees.

Insights from Genome Comparisons

  • Chromosome Comparisons:

    • Human chromosomes share significant organization similarities with those of chimpanzees and gorillas.

Evidence of Divergence through Transposons

  • Transposons in Genomes:

    • Comparing the positions of transposons in human and mouse genomes illustrates evolutionary divergence.

Pufferfish Genome Characteristics

  • Fugu (Pufferfish) Genome:

    • Compact genome yet similar gene numbers to larger species like zebrafish; exhibits reduced junk DNA.

Conservation of Gene Positions

  • Introns in Compact Genomes:

    • Introns of certain genes, like Huntington's, show remarkable conservation between distinct species.

Tree of Life and Genetic Diversity

  • Three Major Divisions of Life:

    • The tree of life summarizes genetic relationships and evolutionary distances based on rRNA sequences.

Complexity of the Human Genome

  • Human Genome Size:

    • The haploid human genome contains approximately 3.2 billion nucleotide pairs; extensive in both size and gene diversity.

Chromosome 22 and Gene Sequencing

  • Chromosome 22 Details:

    • First human chromosome sequenced with significant data on its structure, including genes and regulatory sequences.

Statistics of the Human Genome

  • Vital Genome Statistics:

    • ~19,000 protein-coding genes, about 5,000 non-coding genes, and a chromosome structure rich in regulatory and repetitive sequences.

Repetitive DNA Sequences

  • Human Genome Composition:

    • A large portion of the genome comprises repetitive non-coding sequences and introns.

Gene Prediction Algorithms

  • Gene Detection Techniques:

    • Computer programs analyze DNA sequences to predict gene locations, utilizing reading frames and stop/start codons.

Single Nucleotide Polymorphisms (SNPs)

  • SNP Characteristics:

    • SNPs arise from single nucleotide variations and are valuable in genetic studies, including fingerprinting.

Alternative RNA Splicing

  • Complex Protein Production:

    • Alternative splicing of mRNA allows multiple protein variants to be produced from a single gene, contributing to diversity in gene expression.