Mutations in Genetics

Mutations

• Insertion/deletion mutations alter the sequence of nucleotides after the insertion/deletion point, causing a frameshift.
• Point mutations/substitutions replace one base pair with another.
• Nonsense mutations introduce a stop codon, prematurely ending translation and producing a truncated polypeptide.
• Missense mutations change a codon, resulting in a different amino acid and altered protein tertiary structure.
• Silent mutations change a codon but don't affect the amino acid sequence produced. This is possible due to the degenerate nature of the genetic code.
• Mutations can have neutral effects if they occur in non-coding regions, are silent mutations, or don't affect the organism's function.
• Beneficial mutations can lead to advantageous traits, like trichromatic vision in humans.
• Harmful mutations can cause diseases like cystic fibrosis due to a mutation in the CFTR protein. The effect of a mutation depends on the environment.

Gene Expression Control

• Gene expression is controlled at transcriptional, post-transcriptional, and post-translational levels.
• The lac operon in E. coli is an example of transcriptional control. It's a DNA segment with structural genes and control sites regulating the expression of beta-galactosidase, which breaks down lactose.
• The operon includes a promoter region for RNA polymerase binding, an operator region for inhibitor binding, and structural genes for three products: beta-galactosidase, lactose permease, and another enzyme.
• The inhibitor protein is coded by a regulator gene located outside the operon.

Cellular Processes

• Apoptosis is programmed cell death that involves:
  • Breakdown of the cell's cytoskeleton, DNA, and proteins.
  • Cell shrinkage and fragmentation.
  • Engulfment and destruction of cell fragments by phagocytes.

Patterns of Inheritance

• Phenotypic variation can be:
  • Discontinuous: Categorical, like shoe size or blood type.
  • Continuous: Quantitative, like height or weight.
• Variation is influenced by both environmental factors (diet, etiolation, chlorosis) and genetic factors.

Sexual Reproduction and Genetic Variation

• Meiosis produces haploid gametes, resulting in genetic variation.
• Crossing over of chromatids during meiosis exchanges genetic material between homologous chromosomes.
• Independent assortment of chromosomes during meiosis creates various combinations of chromosome arrangement.

Key Terms

• Allele: Alternative form of a gene.
• Locus: Specific position of a gene on a chromosome.
• Phenotype: Observable characteristics of an organism, determined by both genotype and environment.
• Genotype: Alleles present within an organism's cells for a specific trait.
• Dominant: Only one allele is needed for the characteristic to be expressed.
• Recessive: The characteristic is expressed only if no dominant allele is present.
• Homozygous: Having two identical alleles.
• Heterozygous: Having two different alleles.
• Codominance: Both alleles contribute to the phenotype.

Linkage

• Linkage occurs when genes for different characteristics are located on the same chromosome and are inherited together.

Evolution

• Natural selection drives evolution through:
  • Phenotypic variation within a population.
  • Environmental change altering selection pressures.
  • Advantageous alleles providing a selective advantage, enabling survival and reproduction.
  • Passing of advantageous alleles to offspring.
  • Changing allele frequency over time and generations.

Factors Affecting Evolution

• Genetic drift: Random changes in allele frequency due to limited reproduction within a population.
• Genetic bottleneck: Rapid population reduction, impacting future population size and genetic variation.
• Founder effect: Reduced genetic diversity when a population is derived from a small number of ancestors.

Speciation

• Speciation is the process of forming new species through reproductive isolation.
• Allopatric speciation: Physical barriers separate populations, leading to different selection pressures and eventual reproductive isolation.
• Sympatric speciation: New species evolve within the same geographic area, often due to chromosomal errors during cell division.

Artificial Selection

• Artificial selection involves humans creating selection pressures to breed desired characteristics.
• Examples include:
  • Dairy cows: Breeding for high milk yield through selective breeding, hormone treatment, and in vitro fertilization.
  • Bread wheat: Developing hexaploid bread wheat through hybridization of wild wheat species.

DNA Sequencing

• DNA sequencing involves determining the order of nucleotides in a DNA molecule.
• Mapping uses existing genomic information to locate specific genes.
• Genomic DNA library: Fragments of DNA are inserted into bacterial artificial chromosomes, creating a collection of cloned DNA segments.
• Sanger sequencing: Uses chain-termination nucleotides to create DNA fragments of varying lengths, which are then separated by electrophoresis and visualized under UV light.
• High-throughput sequencing: Advanced techniques enable rapid and complete genome sequencing.
• Genome-wide comparisons between individuals and species can reveal evolutionary relationships and identify genetic variations associated with diseases.

DNA Profiling

• DNA profiling uses unique DNA characteristics to identify individuals or establish genetic relationships.
• Polymerase chain reaction (PCR): Amplifies DNA by creating millions of copies. Steps:
  • Mixing DNA sample, primers, nucleotides, and DNA polymerase.
  • Heating to separate DNA strands.
  • Cooling to allow primers to bind.
  • Heating to optimal temperature for DNA polymerase activity.
  • Repeating cycle for 30 repetitions.
• Gel electrophoresis: Separates DNA fragments based on size using an electric current.

Genetic Engineering

• Restriction enzymes: Used to cut DNA at specific base sequences.
• Vectors: Used to carry DNA into host cells.
  • Plasmids: Circular DNA molecules found in bacteria.
  • Viruses: Can deliver genes into host cells.

This quiz covers various types of mutations in genetics, including insertion/deletion mutations, point mutations, and their effects on protein synthesis. Explore concepts such as nonsense, missense, silent, and their implications for organisms. Test your understanding of how mutations can be neutral, beneficial, or harmful.