IB/AP Biology Study Guide: DNA, Genetics, and Techniques

DNA

A double helix composed of nucleotides (sugar, phosphate, nitrogenous base).

Helicase

Unzips DNA strands.

Primase

Lays down RNA primer.

DNA Polymerase III

Adds nucleotides in the 5' to 3' direction.

Leading Strand

Continuous replication.

Lagging Strand

Okazaki fragments joined by Ligase.

DNA Polymerase I

Replaces RNA primers with DNA.

Topoisomerase

Prevents supercoiling of DNA ahead of replication fork.

Single-Stranded Binding Proteins (SSBs)

Prevents reannealing of DNA strands.

Telomerase

Enzyme that extends telomeres to prevent chromosome shortening.

DNA Proofreading & Repair Mechanisms

DNA polymerases have exonuclease activity for error correction.

Okazaki Fragment Processing

DNA polymerase I and RNase H remove RNA primers.

Law of Segregation

Each allele separates during gamete formation.

Law of Independent Assortment

Genes for different traits assort independently.

Monohybrid Cross

Involves one gene (3:1 phenotype ratio).

Dihybrid Cross

Involves two genes (9:3:3:1 ratio).

Punnett Squares

Used to predict offspring genotype and phenotype.

Incomplete Dominance

Blending of traits (e.g., red + white = pink flowers).

Codominance

Both alleles expressed (e.g., blood type AB).

Polygenic Inheritance

Multiple genes influence a trait (e.g., skin color).

Pleiotropy

One gene affects multiple traits.

Epistasis

One gene affects the expression of another gene.

Chi-Square Analysis

Used to determine statistical significance of inheritance patterns.

Lethal Alleles

Some alleles cause death when homozygous.

Linked Genes

Inherited together on the same chromosome.

Crossing Over

Can separate linked genes (recombination frequency correlates with gene distance).

Nondisjunction

Failure of chromosomes to separate properly.

Deletion

Loss of a segment.

Duplication

Repetition of a segment.

Inversion

Reversed segment.

Translocation

Segment moves to another chromosome.

Gene Mapping

Based on recombination frequency.

Aneuploidy

Chromosome number variations in plants and animals.

Polyploidy

Chromosome number variations in plants and animals.

Mutagenic Factors

UV radiation, chemicals, and viruses affecting DNA.

Transcription

RNA polymerase synthesizes mRNA from DNA template.

Translation

Ribosomes read mRNA codons.

tRNA

Brings amino acids during translation.

Post-Transcriptional Modifications

mRNA splicing, addition of 5' cap and poly-A tail.

Alternative Splicing

Allows multiple proteins from one gene.

Operon Models

Regulation of gene expression in prokaryotes (lac and trp operon).

Gel Electrophoresis

Separates DNA by size using an electric field.

PCR (Polymerase Chain Reaction)

Amplifies small DNA samples.

CRISPR

Gene-editing tool that modifies DNA sequences.

Sanger Sequencing

Determines DNA sequence using chain termination.

Next-Generation Sequencing (NGS)

Faster, high-throughput DNA sequencing.

Gene Therapy

Corrects genetic disorders through DNA modification.

Telomerase

Function in DNA replication.