Study Notes: DNA replication, Types of Mutations, Natural & Artificial Selection Summary & Study Notes

T4L4 - Types of Mutations ✅

• What this source covers:
  • Introduces how changes in DNA cause changes in proteins and traits.
  • Explains types of gene mutations (substitution, insertion, deletion) and their effects (harmful, neutral, beneficial).

Atomic foundations (smallest pieces)

• DNA is a long molecule made of a sequence of chemical letters called bases (A, T, C, G).
• A gene is a short DNA segment that codes for a protein by specifying an amino-acid sequence.
• Protein shape and function depend on the order of amino acids; changing one amino acid can change the protein.

What a mutation is (explain before the word)

• Sometimes the order of DNA letters changes by accident or by the environment; that change can alter the protein built from the gene.
• After that explanation, the word: mutation = any change in the DNA sequence of a gene or chromosome.

Types of small changes (build one on another)

• Substitution: one base is replaced by another.
  • Example: original GAA → mutated GUA (one base different).
  • Effect: may change one amino acid or may not change the protein (depends on codon redundancy).
• Insertion: an extra base is added into the sequence.
  • Effect: can shift every following grouping of three bases (this is a frame shift) and usually changes many amino acids.
• Deletion: a base is lost.
  • Effect: often causes a frame shift and large changes to the protein.

Inherited vs acquired (small pieces)

• Inherited mutation: present in parents’ sex cells and passed to offspring; found in every cell of the child.
• Acquired (somatic) mutation: occurs during the individual’s life (e.g., UV damage); affects only some cells and is passed on only if it happens in sex cells.

Protein change & "jumping genes"

• Changing an amino-acid sequence can change protein function; sometimes no visible effect.
• Some genes can move to a new location on the genome ("jumping genes").
  • If moved, a gene may be read in a new place or stop working, changing traits.
  • Scientists think jumping genes can create new variation over time.

Worked example from the slides (step-by-step)

Problem: Given DNA -> write complementary mRNA, split into codons, list amino acids

• Given DNA: TAC TTT GGC ATA

Solution:

1. Complementary mRNA: pair each DNA base with RNA base (A↔U, T↔A, C↔G, G↔C).
   • TAC → AUG
   • TTT → AAA
   • GGC → CCG
   • ATA → UAU
   • mRNA sequence: AUG AAA CCG UAU
2. Divide into codons: AUG | AAA | CCG | UAU
3. Translate each codon (use codon chart):
   • AUG = methionine (start, Met)
   • AAA = lysine (Lys)
   • CCG = proline (Pro)
   • UAU = tyrosine (Tyr)
   • Amino acid sequence: Met - Lys - Pro - Tyr
4. What if one codon is written incorrectly?
   • If substitution changes a single base, that codon might code for a different amino acid (possible small change).
   • If insertion/deletion shifts the reading frame, every downstream amino acid changes (usually big effect).

Quick classification tips (useful for exercises)

• If a base is missing → deletion.
• If an extra base appears → insertion.
• If one base is swapped for another → substitution.
• Look at whether downstream codons are shifted to spot frame-shift mutations.

Short examples to practice (answers explained)

• Original: TTACGCAAG → Mutated: TTCGCAAG
  • Compare letter-by-letter; an A after the first two T's is missing → this is a deletion.
• Original: TTACGCAAG → Mutated: TTACGCAAC
  • Only the last base changed G→C → substitution.

Key terms to memorize

• mutation, substitution, insertion, deletion, frame shift

W20-D1-T5L2 - Artificial Selection 🌾

• What this source covers:
  • Explains how humans intentionally influence which traits get passed to the next generation (artificial selection).
  • Gives historical examples (Darwin’s pigeons, dogs, corn) and classroom questions about selection patterns.

Basic idea first

• Organisms inherit traits from parents through genes.
• If humans choose which individuals reproduce based on desirable traits, those traits become more common over generations.
• After that explanation, the term: artificial selection = humans intentionally choosing parents to pass on desired traits.

How it works (step-by-step)

1. Identify a trait humans want to increase (e.g., more eggs, bigger corn kernels).
2. Select parent organisms that show that trait strongly.
3. Breed only those parents for the next generation.
4. Repeat selection over many generations until the trait is prevalent.

• Result: population becomes more like the chosen ideal (can be fast with modern technologies).

Examples from the slides (short and clear)

• Darwin bred pigeons for large, fan-shaped tails to get more tail feathers over generations.
• Dogs: humans selected wolves/dogs with desirable behaviors and features (size, temperament, herding) to develop breeds.
• Corn and cabbage: farmers picked plants with desirable seed size or leaf form to create crops like broccoli and cauliflower.
• Quagga-like zebras: selecting zebras with fewer stripes and tan color produced offspring more like the quagga over generations.

Compare natural vs artificial selection (table style)

• Natural selection: environment 'selects' traits that help survival and reproduction.
• Artificial selection: humans select traits to meet human needs or preferences.
• Both change trait frequencies, but the selecting agent differs (nature vs humans).

Classroom question answers (from slides)

• Which statement best describes how natural selection works?
  • Answer: c) Individuals with helpful traits are more likely to survive and reproduce.
• Pattern when after pollution more large fish survive:
  • Answer: b) Directional selection (population shifts toward larger size).
• Beak size example (extremes favored):
  • Answer: c) Disruptive selection (both extremes increase).
• Human birth weight example (average favored):
  • Answer: b) Stabilizing selection (extremes decrease).
• If a species can't adapt to change:
  • Answer: it can decline and possibly go extinct.

Scenario questions solved (step-by-step)

Problem: Farmer breeds only chickens that lay the most eggs. What method is he using and how does it affect inheritance?

Solution:

1. Method: Selective breeding (a form of artificial selection).
2. How it affects inheritance: By breeding only high-egg producers, alleles for high egg-laying increase in frequency so future generations have more chickens that lay many eggs.
3. Evidence: repeated selection concentrates the desired genes in the population.

Problem: How did dog breeds change from wolves?

Solution:

1. Humans chose wolves/dogs with traits like tameness, size, or hunting ability.
2. Repeated mating of selected individuals concentrated those traits.
3. Over many generations, different breeds emerged specialized for tasks (herding, hunting, companionship).

Key terms to memorize

• artificial selection, selective breeding, domestication

W18-D4-T4L3 - DNA Replication 🧬

• What this source covers:
  • Explains how DNA makes an identical copy of itself before cell division.
  • Compares DNA and RNA and gives step-by-step replication mechanics.

Foundational pieces

• DNA stores genetic information in a sequence of bases; RNA helps read and carry instructions to make protein.
• Base-pairing rules: A pairs with T, and C pairs with G (in DNA). In RNA, A pairs with U instead of T.
• After those basics, the term: DNA replication = the process that makes an exact copy of DNA before a cell divides.

Compare DNA vs RNA (small table idea)

• DNA:
  • Two strands (double helix)
  • Sugar: deoxyribose
  • Bases: A, T, C, G
  • Location: nucleus (in eukaryotes)
  • Function: stores genetic information
• RNA:
  • One strand
  • Sugar: ribose
  • Bases: A, U, C, G
  • Location: nucleus and cytoplasm
  • Function: carries and helps translate genetic instructions

Steps of DNA replication (numbered, simple)

1. The double helix unwinds.
2. The two strands unzip when weak hydrogen bonds between bases break.
3. Each original strand acts as a template strand to build a new complementary strand.
4. Free nucleotides pair to each template base following base-pairing rules (A–T, C–G).
5. Two identical DNA molecules form, each with one old strand and one new strand (semi-conservative replication).

When and why it happens

• When: before cell division (so each new cell has a full copy of the genome).
• Why: growth, repair, and replacement of cells require identical genetic instructions in daughter cells.

Short quiz answers from slides (explicit)

• DNA contains the sugar ribose: False (DNA uses deoxyribose).
• RNA uses thymine (T): False (RNA uses uracil U).
• DNA stores genetic information: True.
• Both DNA and RNA contain adenine (A): True.
• RNA is single-stranded: True.
• When does DNA replication occur? Answer: b) Before cell division.
• True or False: DNA replication produces two identical DNA molecules. True (each molecule has one old and one new strand).
• Fill in the blank: A pairs with __ and C pairs with __. Answer: A pairs with T and C pairs with G.

Role of base-pairing (simple explanation)

• Base-pairing ensures that each new strand is complementary to the original, so the genetic code is preserved exactly (with occasional copying errors = mutations).

Key terms to memorize

• DNA replication, template strand, base-pairing

W19-D1-T5L2 - Natural Selection 🦎

• What this source covers:
  • Describes Darwin’s ideas: variation, differential survival, and how populations change over time.
  • Connects mutations and variation to survival and reproduction in specific environments.

Start from the tiniest idea

• Individuals in a population are not identical; small differences exist in traits (this is called variation).
• Some differences help individuals survive or reproduce better in a particular environment.
• After the explanation, the term: natural selection = the process where environmental pressures cause certain heritable traits to become more common.

Darwin’s five key points (simple list)

1. More offspring are produced than survive.
2. Populations have variation among individuals.
3. Some variations are favorable in the environment.
4. Individuals with favorable traits are more likely to survive and reproduce.
5. Over time, the population changes as favorable traits accumulate.

Mutations & their role in variation

• Mutations occur in DNA (answer: a) DNA).
• They are a source of new variation; most have neutral or harmful effects, but some are beneficial and can be selected for.

Short answers & multiple choice from the slides (solved)

• What type of gene mutation: T-G-A-C-C-A → T-G-A-C-C-A-A
  • This adds one base at the end → insertion.
• DNA segment TTACGCAAG → TTCGCAAG
  • One letter removed (A after second T) → deletion.
• DNA segment TTACGCAAG → TTACGCAAC
  • Last base changed G → C → substitution.
• Three possible consequences to changes in DNA:
  1. Harmful (reduces survival/reproduction)
  2. Neutral (no noticeable effect)
  3. Beneficial (improves survival/reproduction)

Example that ties concepts together (nocturnal worms)

• Scenario: A worm species has nocturnal and diurnal individuals.
• If nocturnal individuals survive better in a given environment, their numbers increase because they produce more surviving offspring.
• Over time, nocturnal worms become more common — this is natural selection acting on existing variation.

Using simulations & evidence (how to think like a scientist)

• Test variation by simulating environments where different traits have advantages.
• Record which trait-bearing individuals survive and reproduce.
• Use evidence to explain how trait frequencies changed.

Key terms to memorize

• natural selection, variation, adaptation