/>
Homeβ€ΊBiologyβ€ΊGenetics
🧬 Biology · Genetics

Memory tricks for DNA, heredity & mutations

From Punnett squares to protein synthesis β€” genetics is all about patterns. These memory tricks lock in the rules of inheritance, DNA structure, and gene expression so you can tackle any genetics problem your exam throws at you.

Study with others
πŸ“‹
Genetics Forum
Ask questions Β· Share techniques
 πŸ’¬
Live Study Room
Study together now
🧬 Genetics

Memory Tricks

Proven mnemonics — fast to learn, hard to forget.

πŸŽ₯ How Flashcards Work
A quick walkthrough of tap-to-flip, rating, and how card colors track what you're struggling with.
← Back Next →
Genetics deck1 of 9
Tap to flip
← →
How well do YOU think you know this?
Easy Medium Hard Harder
Tap to flip back
Genetics deck
Easy0
Medium0
Hard0
Harder0
DNA Structure
A pairs with T, G pairs with C β€” "AT the Golf Course"
Adenine-Thymine Β· Guanine-Cytosine β€” Chargaff's Rules
In DNA, base pairing is always A-T (2 hydrogen bonds) and G-C (3 hydrogen bonds). "AT the Golf Course" β€” A-T, the G-C. Purine (A,G) always pairs with Pyrimidine (T,C). In RNA, Uracil replaces Thymine β€” so A pairs with U.
πŸ“– Full Lesson β†’Difficulty: Beginner
Purines (double ring)
Adenine and Guanine β€” remember PuRine = Pure As Gold (A and G). Larger molecules with two fused rings.
Pyrimidines (single ring)
Thymine, Cytosine, Uracil β€” CUT the Py (C, U, T are pyrimidines). Smaller molecules with one ring.
Why 3 H-bonds for G-C?
More hydrogen bonds = stronger pairing. G-C rich regions of DNA are harder to denature β€” important for PCR and melting temperature calculations.
RNA difference
RNA uses Uracil instead of Thymine, and is single-stranded. A still pairs with U in RNA (2 H-bonds). mRNA, tRNA, and rRNA all follow this rule.
πŸŽ₯ Watch Instead
Alex breaks down A-T, G-C pairing with "AT the Golf Course" β€” 3:30.
Flashcard
πŸƒ DNA Structure
DNA base pairing β€” which bases pair?
Tap to flip
πŸƒ Answer
A pairs with T, G pairs with C β€” "AT the Golf Course"
Purines (double ring) β€” Adenine and Guanine β€” remember PuRine = Pure As Gold (A and G). Larger molecules with two fused rings.
Pyrimidines (single ring) β€” Thymine, Cytosine, Uracil β€” CUT the Py (C, U, T are pyrimidines). Smaller molecules with one ring.
Why 3 H-bonds for G-C? β€” More hydrogen bonds = stronger pairing. G-C rich regions of DNA are harder to denature β€” important for PCR and melting temperature calculations.
RNA difference β€” RNA uses Uracil instead of Thymine, and is single-stranded. A still pairs with U in RNA (2 H-bonds). mRNA, tRNA, and rRNA all follow this rule.
Tap to flip back
Mendelian Genetics
Dominant covers Recessive β€” "Big D dominates little d"
Uppercase = dominant allele Β· Lowercase = recessive allele
In Mendelian genetics, uppercase letters represent dominant alleles and lowercase represent recessive. A dominant allele (D) masks the recessive (d) when both are present. Only when an organism is homozygous recessive (dd) will the recessive trait show. Heterozygous (Dd) = dominant phenotype.
πŸ“– Full Lesson β†’Difficulty: Beginner
Homozygous dominant (DD)
Two dominant alleles β€” expresses dominant trait. Cannot carry recessive trait to offspring.
Heterozygous (Dd)
One of each β€” expresses dominant phenotype but carries recessive allele. Also called a "carrier."
Homozygous recessive (dd)
Two recessive alleles β€” only way to express the recessive phenotype. Both parents must carry at least one recessive allele.
Punnett square ratio
Dd Γ— Dd cross gives 1 DD : 2 Dd : 1 dd genotype ratio and 3 dominant : 1 recessive phenotype ratio.
πŸŽ₯ Watch Instead
β–Ά
Video coming soon
This lesson's animated video hasn't been made yet β€” check back soon.
Flashcard
πŸƒ Mendelian Genetics
Dominant vs recessive alleles?
Tap to flip
πŸƒ Answer
Dominant covers Recessive β€” "Big D dominates little d"
Homozygous dominant (DD) β€” Two dominant alleles β€” expresses dominant trait. Cannot carry recessive trait to offspring.
Heterozygous (Dd) β€” One of each β€” expresses dominant phenotype but carries recessive allele. Also called a "carrier."
Homozygous recessive (dd) β€” Two recessive alleles β€” only way to express the recessive phenotype. Both parents must carry at least one recessive allele.
Punnett square ratio β€” Dd Γ— Dd cross gives 1 DD : 2 Dd : 1 dd genotype ratio and 3 dominant : 1 recessive phenotype ratio.
Tap to flip back
DNA Replication
PESA β€” Primers, Enzymes, Strands, Assembly
Primase β†’ Helicase β†’ Polymerase β†’ Ligase β€” replication order
DNA replication steps: Helicase unwinds the double helix, Primase lays down RNA primers, DNA Polymerase adds new nucleotides (5'β†’3' only), and Ligase seals the gaps between Okazaki fragments on the lagging strand. Replication is semi-conservative β€” each new DNA molecule has one old and one new strand.
πŸ“– Full Lesson β†’Difficulty: Intermediate
Leading vs lagging strand
Leading strand: synthesized continuously toward replication fork. Lagging strand: synthesized in Okazaki fragments away from fork. Both made 5'β†’3'.
Semi-conservative replication
Each daughter DNA has one original parental strand and one new strand. Proven by Meselson-Stahl experiment using heavy nitrogen (¹⁡N).
DNA Polymerase III
Main replication enzyme in prokaryotes. Adds nucleotides 5'β†’3', has proofreading ability (3'β†’5' exonuclease). Cannot start a new strand β€” needs a primer.
Telomeres
Repetitive sequences at chromosome ends that shorten with each replication. Telomerase enzyme rebuilds them in stem cells and cancer cells.
πŸŽ₯ Watch Instead
β–Ά
Video coming soon
This lesson's animated video hasn't been made yet β€” check back soon.
Flashcard
πŸƒ DNA Replication
PESA
Tap to flip
πŸƒ Answer
PESA β€” Primers, Enzymes, Strands, Assembly
Leading vs lagging strand β€” Leading strand: synthesized continuously toward replication fork. Lagging strand: synthesized in Okazaki fragments away from fork. Both made 5'β†’3'.
Semi-conservative replication β€” Each daughter DNA has one original parental strand and one new strand. Proven by Meselson-Stahl experiment using heavy nitrogen (¹⁡N).
DNA Polymerase III β€” Main replication enzyme in prokaryotes. Adds nucleotides 5'β†’3', has proofreading ability (3'β†’5' exonuclease). Cannot start a new strand β€” needs a primer.
Telomeres β€” Repetitive sequences at chromosome ends that shorten with each replication. Telomerase enzyme rebuilds them in stem cells and cancer cells.
Tap to flip back
Protein Synthesis
DNA β†’ RNA β†’ Protein: "Don't Rely on Promises"
Transcription (DNA→mRNA) then Translation (mRNA→Protein)
The central dogma: DNA is transcribed into mRNA, which is translated into protein. "Don't Rely on Promises" = DNA β†’ RNA β†’ Protein. Transcription happens in the nucleus; translation happens at ribosomes in the cytoplasm. Each codon (3 bases) codes for one amino acid.
πŸ“– Full Lesson β†’Difficulty: Intermediate
Transcription
RNA Polymerase reads the template strand 3'β†’5' and produces mRNA 5'β†’3'. Promoter region signals start; terminator signals stop. Occurs in nucleus.
mRNA processing
In eukaryotes: 5' cap and poly-A tail added; introns spliced out, exons joined. Mature mRNA exits nucleus through nuclear pores.
Translation
Ribosome reads mRNA codons; tRNA anticodons bring matching amino acids. Start codon = AUG (methionine). Stop codons = UAA, UAG, UGA (U Are Awful, U Are Gone, U Go Away).
Genetic code
64 possible codons (4Β³) code for 20 amino acids β€” the code is redundant (degenerate). Most amino acids have multiple codons. The code is nearly universal across all life.
πŸŽ₯ Watch Instead
β–Ά
Video coming soon
This lesson's animated video hasn't been made yet β€” check back soon.
Flashcard
πŸƒ Protein Synthesis
Protein synthesis β€” the flow of information?
Tap to flip
πŸƒ Answer
DNA β†’ RNA β†’ Protein: "Don't Rely on Promises"
Transcription β€” RNA Polymerase reads the template strand 3'β†’5' and produces mRNA 5'β†’3'. Promoter region signals start; terminator signals stop. Occurs in nucleus.
mRNA processing β€” In eukaryotes: 5' cap and poly-A tail added; introns spliced out, exons joined. Mature mRNA exits nucleus through nuclear pores.
Translation β€” Ribosome reads mRNA codons; tRNA anticodons bring matching amino acids. Start codon = AUG (methionine). Stop codons = UAA, UAG, UGA (U Are Awful, U Are Gone, U Go Away).
Genetic code β€” 64 possible codons (4Β³) code for 20 amino acids β€” the code is redundant (degenerate). Most amino acids have multiple codons. The code is nearly universal across all life.
Tap to flip back
Mutations
Point mutations: Silent, Missense, Nonsense β€” "Students Miss Nothing"
Silent = same AA Β· Missense = different AA Β· Nonsense = stop codon
Three types of point mutations by effect: Silent mutations change a codon but code for the same amino acid (due to redundancy). Missense mutations change one amino acid for another. Nonsense mutations create a premature stop codon, truncating the protein. Frameshift mutations (insertions/deletions) are typically most damaging.
πŸ“– Full Lesson β†’Difficulty: Intermediate
Frameshift mutations
Insertions or deletions that shift the reading frame β€” all downstream codons change. Usually catastrophic to protein function. Sickle cell is NOT a frameshift β€” it's a missense point mutation.
Sickle cell anemia
Classic missense mutation — single base change (A→T) converts glutamic acid to valine in hemoglobin β chain. Causes RBCs to sickle under low oxygen. Heterozygotes have malaria resistance.
Mutagens
Chemical mutagens (base analogs, alkylating agents), radiation (UV causes thymine dimers, X-rays cause breaks), and biological mutagens (transposons, viruses).
Proofreading and repair
DNA polymerase proofreads during replication. Mismatch repair, base excision repair, and NER (nucleotide excision repair) fix errors after replication. XP (xeroderma pigmentosum) = defective NER.
πŸŽ₯ Watch Instead
β–Ά
Video coming soon
This lesson's animated video hasn't been made yet β€” check back soon.
Flashcard
πŸƒ Mutations
Point mutations β€” the three types?
Tap to flip
πŸƒ Answer
Point mutations: Silent, Missense, Nonsense β€” "Students Miss Nothing"
Frameshift mutations β€” Insertions or deletions that shift the reading frame β€” all downstream codons change. Usually catastrophic to protein function. Sickle cell is NOT a frameshift β€” it's a missense point mutation.
Sickle cell anemia — Classic missense mutation — single base change (A→T) converts glutamic acid to valine in hemoglobin β chain. Causes RBCs to sickle under low oxygen. Heterozygotes have malaria resistance.
Mutagens β€” Chemical mutagens (base analogs, alkylating agents), radiation (UV causes thymine dimers, X-rays cause breaks), and biological mutagens (transposons, viruses).
Proofreading and repair β€” DNA polymerase proofreads during replication. Mismatch repair, base excision repair, and NER (nucleotide excision repair) fix errors after replication. XP (xeroderma pigmentosum) = defective NER.
Tap to flip back
Inheritance Patterns
X-linked recessive: "Daughters carry, Sons suffer"
X-linked traits affect males more β€” they only have one X chromosome
X-linked recessive conditions (hemophilia, color blindness, Duchenne MD (muscular dystrophy)) affect males (XY) far more than females (XX) because males only have one X β€” if it carries the recessive allele, the trait is expressed. Females need two copies to be affected. Carrier females (X^A X^a) pass the gene to 50% of sons.
πŸ“– Full Lesson β†’Difficulty: Intermediate
Autosomal dominant
One copy sufficient to express trait. Affects every generation. Huntington's, Marfan syndrome, achondroplasia. Affected parent has 50% chance of passing to each child.
Autosomal recessive
Two copies needed. Can skip generations. Cystic fibrosis, PKU (phenylketonuria β€” an inherited metabolic disorder), sickle cell. Carrier parents (Aa Γ— Aa) have 25% affected, 50% carrier, 25% unaffected offspring.
Codominance vs incomplete dominance
Codominance: both alleles expressed equally (AB blood type). Incomplete dominance: blend of traits (red + white = pink snapdragons). Neither allele fully dominates.
Mitochondrial inheritance
mtDNA inherited only from mother β€” all offspring of affected mother are affected. Leber's hereditary optic neuropathy. Passed through egg, not sperm.
πŸŽ₯ Watch Instead
β–Ά
Video coming soon
This lesson's animated video hasn't been made yet β€” check back soon.
Flashcard
πŸƒ Inheritance Patterns
X-linked recessive β€” who carries it, who is affected?
Tap to flip
πŸƒ Answer
X-linked recessive: "Daughters carry, Sons suffer"
Autosomal dominant β€” One copy sufficient to express trait. Affects every generation. Huntington's, Marfan syndrome, achondroplasia. Affected parent has 50% chance of passing to each child.
Autosomal recessive β€” Two copies needed. Can skip generations. Cystic fibrosis, PKU (phenylketonuria β€” an inherited metabolic disorder), sickle cell. Carrier parents (Aa Γ— Aa) have 25% affected, 50% carrier, 25% unaffected offspring.
Codominance vs incomplete dominance β€” Codominance: both alleles expressed equally (AB blood type). Incomplete dominance: blend of traits (red + white = pink snapdragons). Neither allele fully dominates.
Mitochondrial inheritance β€” mtDNA inherited only from mother β€” all offspring of affected mother are affected. Leber's hereditary optic neuropathy. Passed through egg, not sperm.
Tap to flip back
Meiosis
PMAT twice β€” "People Meet And Talk, People Meet And Talk"
Prophase Β· Metaphase Β· Anaphase Β· Telophase Γ— 2 (Meiosis I and II)
Meiosis has two divisions: Meiosis I separates homologous chromosomes (reduces chromosome number by half), and Meiosis II separates sister chromatids (like mitosis). Result: 4 haploid cells (n) from 1 diploid cell (2n). Key event in Prophase I = crossing over (genetic recombination), which increases genetic diversity.
πŸ“– Full Lesson β†’Difficulty: Intermediate
Meiosis I vs Mitosis
Key difference: in Meiosis I, homologous chromosomes pair up (synapsis) and cross over. Homologs separate, not sister chromatids. Result is 2 haploid cells, each with duplicated chromosomes.
Crossing over
Occurs at chiasmata during Prophase I. Homologous chromosomes exchange segments β€” creates new allele combinations. Greater distance between genes = more crossing over = higher recombination frequency.
Independent assortment
During Metaphase I, homolog pairs align randomly β€” either chromosome of each pair can go to either pole. Produces 2^n combinations (2^23 = 8 million for humans). Explains Mendel's second law.
Nondisjunction
Failure of chromosomes to separate properly during meiosis. Produces aneuploid gametes. Trisomy 21 (Down syndrome) results from nondisjunction of chromosome 21 during meiosis I.
πŸŽ₯ Watch Instead
β–Ά
Video coming soon
This lesson's animated video hasn't been made yet β€” check back soon.
Flashcard
πŸƒ Meiosis
Meiosis β€” how many divisions, and the phases?
Tap to flip
πŸƒ Answer
PMAT twice β€” "People Meet And Talk, People Meet And Talk"
Meiosis I vs Mitosis β€” Key difference: in Meiosis I, homologous chromosomes pair up (synapsis) and cross over. Homologs separate, not sister chromatids. Result is 2 haploid cells, each with duplicated chromosomes.
Crossing over β€” Occurs at chiasmata during Prophase I. Homologous chromosomes exchange segments β€” creates new allele combinations. Greater distance between genes = more crossing over = higher recombination frequency.
Independent assortment β€” During Metaphase I, homolog pairs align randomly β€” either chromosome of each pair can go to either pole. Produces 2^n combinations (2^23 = 8 million for humans). Explains Mendel's second law.
Nondisjunction β€” Failure of chromosomes to separate properly during meiosis. Produces aneuploid gametes. Trisomy 21 (Down syndrome) results from nondisjunction of chromosome 21 during meiosis I.
Tap to flip back
Gene Regulation
Lac operon: No lactose = repressor ON = genes OFF
Negative control β€” repressor blocks transcription when lactose absent
The lac operon in E. coli is the classic gene regulation example. When lactose is absent, the repressor protein binds the operator and blocks RNA polymerase β€” genes are OFF. When lactose is present, allolactose binds the repressor, inactivating it β€” genes turn ON. The cell only makes lactose-digesting enzymes when lactose is available.
πŸ“– Full Lesson β†’Difficulty: Advanced
Operon structure
Promoter β†’ Operator β†’ Structural genes (lacZ, lacY, lacA). Regulator gene produces repressor protein separately. RNA polymerase binds promoter; repressor blocks operator.
Catabolite repression (CAP)
When glucose is present, cAMP levels drop β†’ CAP cannot bind β†’ reduced transcription even if lactose present. Cell prefers glucose. Double control: repressor (negative) + CAP (positive).
Trp operon (repressible)
Opposite of lac operon. When tryptophan is abundant, it acts as corepressor β€” activates repressor β†’ genes OFF. When tryptophan is scarce, repressor inactive β†’ genes ON. Makes tryptophan when needed.
Eukaryotic regulation
More complex: transcription factors, enhancers, silencers, chromatin remodeling, DNA methylation, histone acetylation. Gene expression can be regulated at transcription, processing, transport, translation, and protein levels.
πŸŽ₯ Watch Instead
β–Ά
Video coming soon
This lesson's animated video hasn't been made yet β€” check back soon.
Flashcard
πŸƒ Gene Regulation
Lac operon β€” what happens without lactose?
Tap to flip
πŸƒ Answer
Lac operon: No lactose = repressor ON = genes OFF
Operon structure β€” Promoter β†’ Operator β†’ Structural genes (lacZ, lacY, lacA). Regulator gene produces repressor protein separately. RNA polymerase binds promoter; repressor blocks operator.
Catabolite repression (CAP) β€” When glucose is present, cAMP levels drop β†’ CAP cannot bind β†’ reduced transcription even if lactose present. Cell prefers glucose. Double control: repressor (negative) + CAP (positive).
Trp operon (repressible) β€” Opposite of lac operon. When tryptophan is abundant, it acts as corepressor β€” activates repressor β†’ genes OFF. When tryptophan is scarce, repressor inactive β†’ genes ON. Makes tryptophan when needed.
Eukaryotic regulation β€” More complex: transcription factors, enhancers, silencers, chromatin remodeling, DNA methylation, histone acetylation. Gene expression can be regulated at transcription, processing, transport, translation, and protein levels.
Tap to flip back
Biotechnology
PCR = "Photocopier for DNA" β€” denature, anneal, extend
Polymerase Chain Reaction β€” amplifies specific DNA sequences exponentially
PCR copies a specific DNA segment millions of times. Three steps cycle repeatedly: Denaturation (heat to 94Β°C separates strands), Annealing (cool to ~55Β°C β€” primers attach), Extension (heat to 72Β°C β€” Taq polymerase extends). Each cycle doubles the DNA β€” 30 cycles = 2³⁰ = over 1 billion copies from a single template.
πŸ“– Full Lesson β†’Difficulty: Advanced
Why Taq polymerase?
Isolated from Thermus aquaticus β€” a bacterium living in hot springs. Heat-stable, survives the 94Β°C denaturation step. Regular DNA polymerase would denature and stop working.
Gel electrophoresis
Separates DNA fragments by size. Smaller fragments migrate farther through agarose gel toward positive electrode. DNA ladder provides size reference. Used to visualize PCR products.
Restriction enzymes
Cut DNA at specific palindromic sequences. EcoRI cuts at GAATTC. Produce sticky ends that can be joined to other DNA cut with the same enzyme. Foundation of recombinant DNA technology.
CRISPR-Cas9
Guide RNA directs Cas9 protein to specific DNA sequence. Cas9 cuts both strands. Cell repairs by NHEJ (Non-Homologous End Joining β€” error-prone, disables gene) or HDR (Homology-Directed Repair β€” can insert new sequence). Revolutionary gene editing tool.
πŸŽ₯ Watch Instead
β–Ά
Video coming soon
This lesson's animated video hasn't been made yet β€” check back soon.
Flashcard
πŸƒ Biotechnology
PCR β€” what is it, and the three steps?
Tap to flip
πŸƒ Answer
PCR = "Photocopier for DNA" β€” denature, anneal, extend
Why Taq polymerase? β€” Isolated from Thermus aquaticus β€” a bacterium living in hot springs. Heat-stable, survives the 94Β°C denaturation step. Regular DNA polymerase would denature and stop working.
Gel electrophoresis β€” Separates DNA fragments by size. Smaller fragments migrate farther through agarose gel toward positive electrode. DNA ladder provides size reference. Used to visualize PCR products.
Restriction enzymes β€” Cut DNA at specific palindromic sequences. EcoRI cuts at GAATTC. Produce sticky ends that can be joined to other DNA cut with the same enzyme. Foundation of recombinant DNA technology.
CRISPR-Cas9 β€” Guide RNA directs Cas9 protein to specific DNA sequence. Cas9 cuts both strands. Cell repairs by NHEJ (Non-Homologous End Joining β€” error-prone, disables gene) or HDR (Homology-Directed Repair β€” can insert new sequence). Revolutionary gene editing tool.
Why can't we make them? β€” Humans lack specific enzymes needed to synthesize the carbon skeletons of essential amino acids. These biosynthetic pathways were lost during evolution β€” easier to obtain from diet. Non-essential amino acids can be synthesized from intermediates of glycolysis and Krebs cycle.
Protein complementation β€” Vegetarians combine incomplete proteins to get all essential amino acids. Examples: rice + beans (rice lacks lysine, beans lack methionine β€” together complete), peanut butter + bread. Don't need to eat at same meal β€” just same day.
Tap to flip back
🎓 Common Exam Questions
0
correct
0
wrong
5
remaining
correct  Β· 
No saved cards yet.
Click β˜† Save on any memory trick to save it here.