2.Mitosis - Meiosis & Genetics

Mitosis vs. Meiosis

🧠 Flashcard Questions Mitosis

• Q: What is the main purpose of mitosis?
  A: Growth and repair

• Q: How many daughter cells are produced in mitosis?
  A: 2

• Q: Are the daughter cells in mitosis diploid or haploid?
  A: Diploid (2n)

• Q: Are mitotic daughter cells genetically identical or different?
  A: Identical

Meiosis

• Q: What is the purpose of meiosis?
  A: To produce gametes for reproduction

• Q: How many divisions occur in meiosis?
  A: Two

• Q: How many daughter cells result from meiosis?
  A: Four

• Q: Are the daughter cells in meiosis haploid or diploid?
  A: Haploid (n)

• Q: Are meiotic daughter cells genetically identical?
  A: No, they are genetically different

📊 Mitosis vs. Meiosis – Table Summary

Feature	Mitosis	Meiosis
Purpose	Growth and repair	Reproduction (gamete formation)
# of Divisions	1	2
# of Daughter Cells	2	4
Chromosome Count in Daughter Cells	Diploid (2n) – same as parent	Haploid (n) – half of the parent
Genetic Identity	Identical to the parent	Genetically different
Occurs In	All somatic (body) cells	Sex cells only (sperm, egg)
Starting Cell	Diploid (2n)	Diploid (2n): Primary spermatocyte or oocyte
Used For	Tissue repair, growth, and asexual reproduction	Sexual reproduction

Mitosis & Meiosis ProPhase (Pro=Pre=Before)

Mitosis Phases

TEAS may test names & order: Prophase, Metaphase, Anaphase, Telophase (PMAT)

Meiosis Phases

Meiosis has two rounds of PMAT: Meiosis I and Meiosis II, each with PMAT steps

🔄 Flow of Cell Division Stages

Mitosis (1 round – for body cells):

P → M → A → T → 2 identical diploid cells

Begins at Prophase

What’s happened? (Refer to Graph):

Mitosis Prophase Phases

Chromosomes become visible as they condense and thicken

Meiosis (2 rounds – for sex cells):

P1 → M1 → A1 → T1 → 2 haploid cells
then
P2 → M2 → A2 → T2 → 4 genetically different haploid cells

Begins at Prophase 1

What’s happened? (Refer to Graph):

Meiosis Prophase Phases 1

Chromosomes’ condensation and pairing of homologous chromosomes. Where crossover occurs.

homologous

同源染色体（细胞生物学）：指在细胞中，一条来自父亲，一条来自母亲，具有相同基因序列和位置的染色体对

Mitosis & Meiosis MetaPhase (M=Middle)

Mitosis MetaPhase

Chromosomes align in the middle of the cell’s center, forming a single row.

Meiosis Metaphase 1

Chromosomes align in the middle of the cell’s center and maintain their homologous pairs.

Mitosis & Meiosis AnaPhase (A=Away)

Mitosis AnaPhase

Chromatids are separated and drawn to the opposite ends of the cell by spindle fibers

Meiosis Anaphase 1

Chromosomes are separated and drawn to the opposite ends of the cell by spindle fibers. #Allows random assortment of chromosomes, contributing to genetic diversity among offspring.

Chromatids = 🧬 What Are Chromatids? ✅ Definition:

A chromatid is one-half of a duplicated chromosome.

When a chromosome is copied (during interphase), it forms two identical sister chromatids, joined at a point called the centromere.

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📘 Simple Breakdown:

Term	Description
Chromosome	A structure made of DNA and proteins that carries genetic info
Chromatid	One copy of a chromosome after it has been duplicated
Sister Chromatids	Two identical chromatids (joined at the centromere)
Centromere	The central part where two sister chromatids are attached

Mitosis & Meiosis TeloPhase

Mitosis TeloPhase

Chromosomes reach the opposite sides of the cell. Forming new nuclear envelopes around the chromosomes.

Meiosis Telophase 1

Chromosomes reach the opposite sides of the cell. Forming new nuclear envelopes around the chromosomes.

Mitosis & Meiosis - Cytokinesis

Mitosis Cytokinesis

Split the cytoplasm of the cell Two identical, diploid cells.

Meiosis Cytokinesis

Split the cytoplasm of the cell

Meiosis Round 2

Meiosis Prophase 2

Chromosome condensation in both cells

Meiosis Metaphase 2

Chromosomes align in the center of the cell. Forming a single row.

Meiosis Anaphase 2

Chromatids are separated and drawn to the opposite ends of the cell by spindle fibers.

Meiosis Teloohase 2

Chromosomes reach the opposite sides of the cell. Forming new nuclear envelopes around the chromosomes.

Meiosis Cytokinesis

Split the cytoplasm of the cell. Four non-identical cells (Gametes)

Heredity

The passing on of physical or mental characteristics genetically from one generation to another.

DNA - Deoxyribonucleic Acid

Nucleotide

Self-replicating material that is present in nearly all living organisms as the main constituent of Chromosomes.

"Nucleotide" 的中文是核苷酸。核苷酸是核酸（如 DNA 和 RNA）的基本組成單位，它由一個含氮鹼基、一個五碳糖和一个或多个磷酸基团组成。

Component	Description	Role/Function
Double Helix Shape	Twisted ladder-like structure	Structure of DNA
Nucleotide 核苷酸	Building block of DNA	Makes up DNA strands
Phosphate	Circle part of nucleotide	Part of DNA backbone
Deoxyribose (A Sugar)	Pentagon-shaped sugar	Bonds phosphate and base (DNA backbone)
Nitrogenous Base	Rectangular structure	Contains genetic code
Code for Traits	Info carried by nitrogenous base	Determines genetic traits

4 Kinds of Bases in DNA

Component	Explanation	Memory Aid
DNA (Deoxyribonucleic Acid)	Self-replicating genetic material found in all living organisms	-
Nucleotide Bases	The rungs of the DNA ladder, paired by hydrogen bonds	-
Adenine (A)	Pairs with Thymine (T)	Apple in the Tree
Thymine (T)	Pairs with Adenine (A)	Apple in the Tree
Cytosine (C)	Pairs with Guanine (G)	Car in the Garage
Guanine (G)	Pairs with Cytosine (C)	Car in the Garage
Hydrogen Bonds	Weak bonds that hold base pairs together	-

A - T

C - G

What is Gene?

The two types of Gene?

🔹 Flashcard-Style Questions:

1. Structural Genes

• Q: What type of gene codes for traits like eye or hair color?

• A: Structural genes.

• Q: Name two functions of proteins coded by structural genes.

• A: Enzymatic activity and defense mechanisms.

2. Regulatory Genes

• Q: What is the role of regulatory genes?

• A: To control the timing, location, and amount of gene expression.

• Q: True or False: Regulatory genes can turn structural genes on or off.

• A: True.

3. Protein and Gene Interaction

• Q: Can proteins influence gene activity?

• A: Yes, proteins can regulate genes or act as products of genes.

4. Gene Regulation

• Q: What is gene regulation?

• A: The control of gene expression in terms of timing, location, and quantity.

• Q: What does gene regulation help an organism do?

• A: Adapt and control development and cellular function.

A unit of Heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring.

Category	Description	Examples/Functions

Structural Genes

Code for proteins that affect the physical traits and basic functions of the body

Eye/hair color, transport proteins, enzymes, immunity

Regulatory Genes

Control when, where, and how much structural genes are expressed

Gene regulation, activation/inactivation

Protein Function

Proteins are made from gene instructions and can also influence other gene functions

Enzymes, transporters, hormones, structural roles

Gene Regulation

The process that determines which genes get turned on or off

Controlled by r

🔹 Extra TEAS-Related Concepts Not in Image:

Concept	Explanation
Transcription	DNA is transcribed into mRNA
Translation	mRNA is translated into proteins at the ribosome
Mutations	Changes in DNA that can affect gene expression or protein function
Epigenetics	Gene expression changes that don’t involve changes to the DNA sequence
Homeobox (HOX) Genes	Regulatory genes that control body plan during embryonic development
Operons (Prokaryotic gene regulation)	Units of genes in bacteria regulated together (e.g., lac operon)

RNA - Ribonucleic Acid

A nucleic acid present in all living cells whose principal role is to act as a messenger carrying instructions from DNA for controlling the synthesis of protein.

Present is both in and outside of the nucleus.

Feature	RNA (Ribonucleic Acid)
Structure	Single-stranded
Sugar	Ribose (different from DNA's deoxyribose)
Base Pairing Rule	Adenine pairs with Uracil (instead of Thymine)
Base Names	Adenine (A), Uracil (U), Cytosine (C), Guanine (G)
Location	Present inside and outside the nucleus
Function	Messenger that carries DNA instructions for protein synthesis
Memory Tip	"Apple under the tree" = A → U

Pairing Tips:

Apple Under the tree

Car in the Garage

3 Types of RNA

Type of RNA	Full Name	Function	Visual Cue from Image
mRNA	Messenger RNA	Carries genetic instructions from DNA( IN NUCLUES ) to the ribosome	Mail carrier
rRNA	Ribosomal RNA	Forms part of the ribosome, the site of protein synthesis	Ribosome base structure
tRNA	Transfer RNA	Transfers amino acids and matches them to mRNA codons	Adaptor decoding mRNA into protein

Transcription vs Translation

🎓 Flashcard Questions

1. Transcription

• Q: Where does transcription occur in the cell?

• A: In the nucleus.

• Q: What enzyme is responsible for transcription?

• A: RNA polymerase.

• Q: What is the result of transcription?

• A: A strand of mRNA.

2. Translation

• Q: What is the purpose of translation?

• A: To build a protein from the sequence on mRNA.

• Q: What molecule brings amino acids to the ribosome?

• A: tRNA (transfer RNA).

• Q: Where does translation take place?

• A: At the ribosome in the cytoplasm.

3. Both Together

• Q: What is the correct order of the processes?

• A: Transcription → Translation.

• Q: What does mRNA do in protein synthesis?

• A: It carries the genetic code from DNA to the ribosome.

Transcription: DNA → mRNA

Translation: mRNA →(Using Ribosome) Protein

Step	Transcription	Translation
Definition	Making an RNA copy of a gene’s DNA sequence	Converting mRNA into a chain of amino acids (protein)
Location	Nucleus (in eukaryotes)	Ribosome (cytoplasm)
Main Molecule	RNA Polymerase	tRNA (transfer RNA) + Ribosome
Product	mRNA (messenger RNA)	Polypeptide (protein chain)
Memory Tip	“C comes before L” → Transcription comes before Translation	Translation happens after transcription

Concept	Details
Codons	3-letter mRNA sequences that code for amino acids
Start Codon	AUG — signals the start of translation
Stop Codons	UAA, UAG, UGA signal the end of translation
Mutation Effect	A DNA mutation can change mRNA → which may alter the amino acid/protein
Role of Ribosomes	Ribosomes "read" mRNA and build proteins with the help of tRNA

RNA Polymerase

🧬 RNA Polymerase – TEAS Exam Breakdown

RNA Polymerase is an enzyme essential in the transcription step of protein synthesis.

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✅ Definition:

RNA Polymerase is the enzyme that:

• Binds to DNA at the start of a gene.

• Unzips the DNA strands.

• Builds a complementary strand of RNA by matching RNA bases to the DNA template strand.

Transcription vs Translation Part 2

Codons, Anticodons, & Translation

🎓 Flashcard Questions

1. Codons & Anticodons

• Q: What is a codon?

  • A: A 3-nucleotide sequence on mRNA that codes for an amino acid.

• Q: Where is the anticodon found?

  • A: On tRNA.

• Q: What does the anticodon do?

  • A: It pairs with the codon to ensure the correct amino acid is added.

2. Translation Process

• Q: What is formed during translation?

  • A: A polypeptide chain (protein).

• Q: What molecule carries amino acids to the ribosome?

  • A: tRNA.

• Q: What signals the end of translation?

  • A: A stop codon.

Summary Table: Codons, Anticodons, & Translation

Term	Definition
Translation	The process of converting mRNA into a chain of amino acids (a protein)
Codon	A 3-letter sequence on mRNA that codes for an amino acid
Anticodon	A complementary 3-letter sequence on tRNA that binds to the codon
tRNA (transfer RNA)	Carries amino acids and matches codons using its anticodon
Polypeptide Chain	A string of amino acids — final product of translation (protein)
Stop Codon	Signals the end of translation — does not code for an amino acid

🧠 Memory Tips:

• Codon = Code (on mRNA)

• Anticodon = Anti-match (on tRNA)

• tRNA = Taxi that drops off the right amino acid

Transcription vs Translation Flow

🧬 Types of Mutations (DNA Level)

Mutations are changes in the DNA sequence, and they can affect proteins in different ways depending on the type.

What are the two categories and what included in each.

🔷 1. DNA-Level Mutations (Type of Base Change)

DNA-Level Categories → Describes what kind of base change happened.

Mutation Type	What It Means
Transition A-A	A purine ↔ purine (A ↔ G) or pyrimidine ↔ pyrimidine (C ↔ T)
Transversion A-B	A purine ↔ pyrimidine (A or G ↔ C or T)

🧠 Key point:
These may or may not affect the protein — they only describe the DNA substitution type.

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🔶 2. Protein-Level Mutations (Effect on Protein)

These describe what happens to the resulting protein after the DNA mutation.

Mutation Type	What It Means
Missense	Base change → changes amino acid
Nonsense	Base change → creates stop codon
Frameshift	Insertion/deletion → shifts reading frame, changing entire protein
Silent	DNA base changes, but amino acid stays the same (due to codon redundancy)

🧠 Key point:
These always affect the protein structure or function.

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✅ How This Helps:

• Transition/transversion = what changed in the DNA

• Silent/missense/nonsense/frameshift = what that change caused

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🧬 Example:

GAG → GTG

• Base A → T = transversion mutation (DNA-level)

• Glutamic acid → valine = missense mutation (protein-level)

💡 Types of Genetic Mutations Quiz

🧬 Sickle Cell Anemia

• Cause: A point mutation (a single base substitution) in the hemoglobin-beta gene.

• Specifically, the DNA mutation changes the codon GAG (which codes for glutamic acid) to GTG (which codes for valine).

• This change causes hemoglobin to form abnormally — leading to sickle-shaped red blood cells.

🧪 Type of Mutation:

This is a missense mutation because:

• The mutation changes one amino acid to another.

• It’s not a silent mutation (which doesn’t change the amino acid).

• It’s not a deletion mutation (which removes a base).

• It’s a substitution, more specifically a:

  • Transversion mutation → a purine is replaced by a pyrimidine, or vice versa.

✅ Correct answer: Transversion mutation

📚 Flashcard-Style Questions for TEAS Practice:

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1. What type of mutation causes sickle cell anemia?

A. Silent mutation
B. Deletion mutation
C. Transition mutation
D. Transversion mutation

✅ Answer: D. Transversion mutation

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2. What happens in a missense mutation?

A. One base is deleted, shifting the reading frame.
B. A base substitution causes one amino acid to change.
C. The sequence of amino acids remains unchanged.
D. The gene is completely removed.

✅ Answer: B. A base substitution causes one amino acid to change.

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3. Which of the following best describes a silent mutation?

A. It changes the amino acid completely.
B. It replaces a purine with a pyrimidine.
C. It changes the DNA base but does not affect the protein.
D. It results in a sickle-shaped red blood cell.

✅ Answer: C. It changes the DNA base but does not affect the protein.

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4. A mutation that results in a stop codon is called:

A. Silent mutation
B. Nonsense mutation
C. Missense mutation
D. Frameshift mutation

✅ Answer: B. Nonsense mutation

🧬 Types of DNA Mutations

Mutation Type	Description	Example	Possible Effect
Substitution	One base (nucleotide) is replaced by another	A → G	Can be silent, missense, or nonsense
Insertion	One or more extra bases are added into the DNA	A → ATG	Can shift the reading frame (frameshift)
Deletion	One or more bases are removed from the DNA	ATG → AG	Can also cause a frameshift
Duplication	A section of DNA is copied and repeated	AT → ATAT	Can alter protein function
Inversion	A segment of DNA is flipped in orientation	ATC → CTA	May disrupt gene regulation or coding
Translocation	A segment of DNA is moved to a different part of the genome (often between chromosomes)	—	Often disrupts multiple genes; may lead to cancer

🧬 Disjunction vs. Nondisjunction

🧬 Disjunction vs. Nondisjunction

Term	Definition	When It Happens	Result
Disjunction	The normal separation of homologous chromosomes or sister chromatids	Meiosis I, Meiosis II, or mitosis	Each daughter cell gets the correct number of chromosomes
Nondisjunction	The failure to separate chromosomes properly	Meiosis I or II, or mitosis	Causes cells with too many or too few chromosomes

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🔬 More Detail: ✅ Disjunction (Normal)

• In Meiosis I: Homologous chromosomes separate

• In Meiosis II: Sister chromatids separate
  ➡ Each gamete gets one copy of each chromosome

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❌ Nondisjunction (Abnormal)

• Homologous chromosomes don’t separate in Meiosis I

• Sister chromatids don’t separate in Meiosis II
  ➡ Gametes end up with 0 or 2 copies of a chromosome instead of 1

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🚨 Results of Nondisjunction

Condition	Chromosome Affected	Result
Down syndrome	Trisomy 21	3 copies of chromosome 21
Turner syndrome	Monosomy X (45,X)	Only one X chromosome in females
Klinefelter syndrome	XXY (47 chromosomes)	Extra X chromosome in males

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🎓 TEAS Tip:

Nondisjunction = incorrect separation

• Happens during anaphase of meiosis or mitosis

• Leads to aneuploidy (abnormal chromosome number)