Mutations in Germ-Line Cells

Mutation and Genetic Variation

• Mutations can occur in primordial germ-line cells, which can result in multiple gametes receiving the mutant gene, increasing its chances of perpetuation.
• The likelihood of a mutant allele being manifested in an organism depends on the dominance of the allele and the stage in the reproductive cycle at which the mutation occurs.
• Mutations in DNA can be passed on to future generations if they occur in cells that will populate the germline.

Human Genetic Diversity

• Genetic diversity and individuality have been maintained throughout evolution due to the steady influx of new nucleotide variation.
• A variant is considered a genetic polymorphism if it is found in more than 1% of chromosomes in the general population.
• Alleles with frequencies of less than 1% are considered rare variants.

Types of Polymorphism

• There are many types of polymorphisms, including those resulting from deletions, duplications, triplications, and other variations of hundreds to millions of base pairs of DNA.
• Some polymorphisms are not associated with a known disease phenotype, while others are rare variants that cause serious illness.

Single Nucleotide Polymorphisms (SNPs)

• SNPs usually have only two alleles, corresponding to different bases occupying a particular location in the genome.
• SNPs are common, occurring on average once every 1000 base pairs, resulting in around 3,000,000 differences between any two human genomes.

Insertion-Deletion Polymorphisms

• Indels are caused by the insertion or deletion of between 2 and 100 nucleotides.
• There are hundreds of thousands of indels in the genome, which can be simple (having only two alleles) or multiallelic.

Microsatellites

• Microsatellites are stretches of DNA consisting of units of two, three, or four nucleotides.
• They are a type of multiallelic indel that can be further subdivided into microsatellite and minisatellite polymorphisms.

Mutation

• Mutations are inherited changes in the genetic material that provide new genetic variation, allowing organisms to evolve.
• Genetic information is accurately duplicated during DNA replication, but heritable changes can occur due to mutations.
• Mutations can be classified into three categories: genome mutations, chromosome mutations, and gene mutations.

Types of Mutations

• Genome mutations affect the number of chromosomes in the cell.
• Chromosome mutations alter the structure of individual chromosomes.
• Gene mutations alter individual genes, including point mutations (nucleotide substitutions, insertions, or deletions).
• RNA processing mutations affect the splicing of introns and exons.
• Nucleotide substitutions can result in missense mutations, chain termination mutations, or RNA processing mutations.

Consequences of Mutations

• Mutations can result in the creation of new alleles, leading to genetic diversity.
• Without mutation, genes would exist in only one form, and populations would not be able to evolve or adapt to environmental changes.
• Mutations can also disrupt the faithful transfer of genetic information from generation to generation.