Quantitative Traits in Genetics

Quantitative Traits

• Phenotypic Variation: Derived from genetic variation, environmental influences, and gene-environment interactions.
• Coefficient of Determination (r²): Measures the proportion of variation in a dependent variable explained by an independent variable.
• Contributing Alleles: Alleles that contribute to the quantitative expression of a trait.
• Correlation Coefficient (r): Measures the strength and direction of the relationship between two variables.
• Covariance: Shows how two traits vary together.
• Expressivity: The degree to which a trait is expressed (constant or variable).
• Genetic Modifiers: Genes that alter the effect of other genes.
• Histogram: A graphical tool to represent trait distributions.
• Mean, Median, Mode: Measures of central tendency (average, middle value, most frequent value).
• Multifactorial Traits: Traits influenced by multiple genes and environmental factors.
• Noncontributing Alleles: Alleles without an effect on the quantitative trait.
• Normal Distribution: A bell-shaped curve depicting trait distributions in populations.
• Penetrance: Proportion of individuals with a specific genotype showing the expected phenotype (complete or incomplete).
• Polygenic Inheritance: Traits controlled by multiple genes.
• Qualitative Traits: Discrete traits, easily categorized (e.g., flower color).
• Quantitative Traits: Traits exhibiting continuous variation (e.g., height, weight).
• Reasons for Phenotypic Variation: Genetic differences, environmental impact, and interactions between genes and environment.
• Scatter Plot: A graph showing relationships between two quantitative traits.
• Trend Line: A line illustrating the general pattern in a scatter plot.
• Variance (s²) / Standard Deviation (s): Measures of variation or spread in data.
• Wild-type Allele: The most common allele in a population.

DNA Replication

• 3' - 5' Exonuclease Activity: Removes mismatched nucleotides for proofreading.
• 5' - 3' Exonuclease Activity: Removes RNA primers during replication.
• ATP: Provides energy for replication processes.
• Bidirectional Replication: Replication proceeds in both directions from the origin.
• Continuous vs. Discontinuous Synthesis: Leading strand synthesized continuously; lagging strand in Okazaki fragments.
• DNA Helicase: Unwinds the DNA double helix.
• DNA Ligase: Joins Okazaki fragments on the lagging strand.
• DNA Polymerase I: Removes primers and fills gaps.
• Klenow Fragment: A portion of DNA Polymerase I with polymerase activity.
• DNA Polymerase III: Main enzyme synthesizing DNA.
• DNA Primase: Synthesizes RNA primers.
• dNTP: Nucleotides used during DNA synthesis.
• Lagging Strand: Synthesized discontinuously.
• Leading Strand: Synthesized continuously.
• Okazaki Fragments: Short DNA segments on the lagging strand.
• Origin of Replication (Ori): Starting point of replication.
• Polymerase Chain Reaction (PCR): A method to exponentially amplify DNA segments.
• Proofreading: Ensures accuracy during DNA replication.
• Replication Bubble: Structure formed at the origin as DNA unwinds.
• Replication Fork: Y-shaped region where DNA replication occurs.
• RNA Primer: Short RNA sequence for DNA polymerase to initiate DNA synthesis.
• Semi-Conservative Model: Each new DNA molecule has one old and one new strand.
• Single-Stranded DNA Binding Proteins: Stabilize single-stranded DNA during replication.
• Template Strand: A DNA strand used as a template for synthesis.

Transcription

• 3' UTR/5' UTR: Non-coding regions affecting mRNA stability and translation.
• 5' Capping: Adds a modified guanine for mRNA stability and ribosome binding.
• Activators/Repressors: Proteins increasing/decreasing transcription.
• Alternative Splicing: Creates different mRNAs from one pre-mRNA.
• Antisense Strand: The DNA strand transcribed into RNA.
• Cis Elements: DNA sequences regulating transcription (e.g., promoters, enhancers).
• Core Promoter: Where RNA polymerase binds for transcription initiation.
• Epigenetic Modifications: Chemical changes to DNA/histones affecting gene expression.
• Exons/Introns: Exons are coding regions; introns are non-coding and removed.
• Mature mRNA: Fully processed mRNA for translation.
• Poly(A) Tail Addition: Protects mRNA, aids in export, and promotes translation.
• Pre-initiation Complex (PIC): Includes RNA polymerase and transcription factors.
• Prokaryotic vs. Eukaryotic Transcription: Prokaryotes lack introns/splicing.
• TATA Box: DNA sequence in promoters for RNA polymerase binding.
• Termination: Ends transcription (Rho-dependent or independent).

Translation

• Amino Acids: Building blocks of proteins with unique side chains.
• Aminoacyl-tRNA: A tRNA molecule carrying an amino acid.
• Codon/Anticodon: mRNA codons pair with tRNA anticodons to specify amino acids.
• Elongation Factors: Help add amino acids to the polypeptide chain.
• Peptide Bond: Links amino acids during protein synthesis.
• Polyribosome: Multiple ribosomes translating the same mRNA.
• Ribosome Structure: Small and large subunits bind mRNA and tRNA for protein synthesis.
• Start Codon/Stop Codon: Start (AUG) initiates, stop codons terminate translation.
• Translation Steps:
• Initiation: Ribosome assembles on mRNA.
• Elongation: Amino acids added to polypeptide chain.
• Termination: Release factors free the completed protein.