Topic: Genes, Chromosomes, and Their Location
Grade Level: 9 | Quarter 1 – Week 3
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📘 PART 1: KEY FACTS (in Quiz Bee Q&A Format)
Q1: What are traits?
🅰️ Traits are observable or inherited characteristics of an organism passed down from parents.
Q2: What carries the genetic instructions in a cell?
🅰️ Chromosomes.
Q3: Where are chromosomes found?
🅰️ In the nucleus of the cell.
Q4: What is the structure within chromosomes that carries the code for traits?
🅰️ Genes.
Q5: What is the location of a gene on a chromosome called?
🅰️ Locus (plural: loci).
Q6: What is an allele?
🅰️ A different form of a gene at the same locus on homologous chromosomes.
Q7: What are homologous chromosomes?
🅰️ A pair of chromosomes with the same genes at the same loci but possibly different alleles.
Q8: What are the building blocks of DNA?
🅰️ DNA bases – Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
Q9: Is gene location random on chromosomes?
🅰️ No, genes are located in specific positions called loci.
Q10: What is the correct order from body to DNA base?
🅰️ Body → Tissues → Cells → Nucleus → Chromosomes → Genes → DNA Molecule → DNA Helix → DNA Bases
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✨ MEMORY AIDS / MNEMONICS
🔤 For DNA bases: A-T, C-G = Always Together, Cute Guys
* A pairs with T
* C pairs with G
🧬 Gene Location Path Mnemonic:
"Big Tall Cats Need Cool Glasses During Happy Days"
Body → Tissues → Cells → Nucleus → Chromosomes → Genes → DNA Molecule → Helix → DNA Bases
💡 Genes vs. Alleles:
* Genes are General instructions (like the recipe).
* Alleles are Alternatives (like chocolate or vanilla flavor of the recipe).
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🎯 STRATEGIC QUIZ TIPS
✅ Tip 1: Memorize the DNA pathway from body to base. It’s often asked in order questions.
✅ Tip 2: Always link locus = location (both start with “L”).
✅ Tip 3: For diagrams, remember:
* Genes are segments of DNA on chromosomes.
* Chromosomes become visible during cell division.
✅ Tip 4: Alleles = variety. If genes are books, alleles are the versions of the story.
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📝 QUICK MATCHING PRACTICE
Term
Match It With
Trait
Inherited characteristic
Chromosome
Carries genes
Nucleus
Contains chromosomes
Locus
Specific gene location
Allele
Alternative gene form
Homologous Chrom.
Pair with same loci
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🧩 BONUS: QUICK TRUE OR FALSE
1. Genes are randomly scattered on chromosomes. → ❌ False
2. Alleles are the exact same in homologous chromosomes. → ❌ Not always
3. Chromosomes are visible during cell division. → ✅ True
4. DNA is found outside the nucleus. → ❌ False (in most cases)
QUIZ BEE REVIEWER
Topic: Non-Mendelian Genetics – Incomplete Dominance and Codominance
Grade 9 | Quarter 1, Week 3
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📌 PART 1: KEY CONCEPTS IN Q&A FORMAT
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👨🔬 BASIC GENETICS
Q1: What is genetics?
🅰️ Genetics is the study of how traits are passed from parents to offspring.
Q2: What is an allele?
🅰️ A different form or variant of a gene.
Q3: What is a phenotype?
🅰️ The observable traits (like eye or hair color) of an organism.
Q4: What is the difference between homozygote and heterozygote?
🅰️
* Homozygote: Two identical alleles (ex. RR or WW)
* Heterozygote: Two different alleles (ex. RW)
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🧬 INCOMPLETE DOMINANCE
Q5: What is incomplete dominance?
🅰️ A pattern of inheritance where both parental traits blend, creating a new trait.
Q6: Give an example of incomplete dominance.
🅰️ Red flower (RR) × White flower (WW) = Pink flower (RW)
Q7: What is the phenotypic ratio of incomplete dominance (RR × WW)?
🅰️ 100% Pink (RW)
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🧬 CODOMINANCE
Q8: What is codominance?
🅰️ A pattern of inheritance where both parental traits appear fully in the offspring.
Q9: Example of codominance?
🅰️ Roan cow (RW) = mix of red and white hairs.
RW × WW = 50% Roan, 50% White
Q10: What happens if two roan cows (RW × RW) are crossed?
🅰️
* 25% Red (RR)
* 50% Roan (RW)
* 25% White (WW)
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✨ MNEMONICS & MEMORY AIDS
🧠 Incomplete Dominance = "In-between"
💡 “INcomplete = IN-between” → a blended or new result (Pink from Red × White)
🧠 Codominance = “Co-captains”
💡 “COdominance = CO-exist” → both traits are shown together (Roan = Red + White patches)
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🔢 QUICK PUNNETT SQUARE REMINDER
Steps:
1. Identify parent genotypes
2. Write the cross (e.g. RW × RW)
3. Set up the grid
4. Fill in offspring genotypes
5. Analyze genotype & phenotype ratios
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🎯 STRATEGIC TIPS
✅ Know the difference:
Type
Outcome
Example
Incomplete Dominance
Blending of traits
Red × White = Pink
Codominance
Both traits fully visible
Red × White = Roan
✅ Watch for ratios:
* RW × RW (incomplete or codominant) = 1:2:1 genotype ratio
* RW × WW = 1:1 genotype and phenotype ratio
✅ Use capital letters consistently:
* R = Red, W = White
* RW = Roan or Pink depending on the context
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📝 QUICK TRUE OR FALSE
1. In incomplete dominance, one allele is completely dominant over the other. → ❌ False
2. In codominance, both alleles are expressed. → ✅ True
3. A heterozygote in incomplete dominance shows a completely new trait. → ✅ True
4. A roan cow is an example of incomplete dominance. → ❌ False (It's codominance)
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🧪 PRACTICE QUESTIONS
Q1: What is the phenotype of a RW flower in incomplete dominance?
🅰️ Pink
Q2: If two RW roan cows mate, what is the chance their calf will be red?
🅰️ 25%
Q3: What genotype results in a white cow in codominance?
🅰️ WW
Q4: What is the genotype ratio when a RW cow is crossed with a WW cow?
🅰️ 1 RW : 1 WW
QUIZ BEE REVIEWER
Topic: Genetic Linkage & Multiple Alleles
Grade 9 | Quarter 1 – Week 3
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📌 PART 1: KEY FACTS (Q&A FORMAT)
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🔗 GENETIC LINKAGE
Q1: What is genetic linkage?
🅰️ Linked genes are genes located close together on the same chromosome and are likely to be inherited together.
Q2: Are all genes on the same chromosome always linked?
🅰️ No. Genes that are far apart can be separated during homologous recombination.
Q3: What process can separate linked genes during gamete formation?
🅰️ Homologous recombination.
Q4: What are sister chromatids?
🅰️ Identical copies of a chromosome created before cell division.
Q5: During recombination, what happens to the chromosomes?
🅰️ They swap large sections of DNA, rearranging the alleles.
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🔁 HOMOLOGOUS RECOMBINATION
Q6: When does homologous recombination occur?
🅰️ During the formation of gametes (egg and sperm).
Q7: What is the result of homologous recombination?
🅰️ New combinations of alleles while keeping the same gene sequence.
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🔢 MULTIPLE ALLELES
Q8: What is meant by “multiple alleles”?
🅰️ A trait controlled by more than two alleles, although only two are present in each individual.
Q9: Example of a trait with multiple alleles?
🅰️ Blood type in humans (IA, IB, i).
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🩸 BLOOD TYPE GENETICS
Blood Type
Genotype(s)
A
IAIA, IAi
B
IBIB, IBi
AB
IAIB
O
ii
Q10: What genotypes produce blood type AB?
🅰️ IAIB
Q11: What genotype results in blood type O?
🅰️ ii
Q12: Is it possible for parents with IAIB and ii genotypes to have a child with blood type B?
🅰️ Yes, 50% chance (child’s genotype: IBi)
Q13: A man with type B (IBi) marries a type O woman (ii). What are the possible genotypes of their children?
🅰️ IBi (type B) and ii (type O)
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🎯 STRATEGIC TIPS
✅ Linked genes don’t follow Mendel’s Law of Independent Assortment because they are inherited together unless recombined.
✅ Always use Punnett Squares to solve blood type problems and show probability clearly.
✅ Remember: Only ii = type O. If neither parent has an i allele, the child can’t be type O.
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✨ MNEMONICS & MEMORY AIDS
🧠 For Blood Types:
"A, B, AB, O = Always Be Aware of Outcomes"
* IA, IB, i = three alleles
* But only two alleles per person (ex: IAi)
🔁 Genetic Linkage:
"Link = Locked Together" → linked genes are locked close and inherited together
"Recombination = Remix" → genes are shuffled during recombination
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📝 QUICK TRUE OR FALSE
1. Genes on different chromosomes are always linked. → ❌ False
2. Recombination mixes up alleles without changing gene order. → ✅ True
3. A person can inherit more than two alleles. → ❌ False (Only two per trait, even if more exist)
4. Type O blood can have genotype IAIB. → ❌ False (only ii is O)
5. Linked genes may be inherited separately if far apart. → ✅ True
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🧪 PRACTICE QUESTIONS
Q1: What are the chances of having a blood type O child from a Type B (IBi) and Type A (IAi) couple?
🅰️ 25%
Q2: If both parents are type AB, what blood type is impossible in their child?
🅰️ Type O (no i allele)
Q3: Which process increases variation among offspring through allele mixing?
🅰️ Homologous recombination
Q4: What type of inheritance pattern includes traits like blood type that involve more than two alleles?
🅰️ Multiple alleles
QUIZ BEE REVIEWER: SEX-LINKED TRAITS & NON-MENDELIAN GENETICS
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📘 I. KEY CONCEPTS SUMMARY
1. Sex-Linked Traits
* Traits whose genes are found on the sex chromosomes (X or Y).
* X-linked: Most sex-linked traits are carried on the X chromosome.
* Y-linked: Traits only found in males, passed from father to son.
2. Common Sex-linked Disorders
Trait
Chromosome
Description
Color-blindness
X
Difficulty distinguishing colors (often red-green)
Hemophilia
X
Blood doesn't clot properly
Hypertrichosis (hairy ears)
Y
Excessive hair growth on ears (only in males)
3. Genotype Notation (X-linked)
Trait
Male
Female
Normal
XᴴY or XᶜY
XᴴXᴴ or XᶜXᶜ
Affected
XʰY
XʰXʰ
Carrier (female only)
—
XᴴXʰ or XᶜX
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🧠 MNEMONICS / MEMORY AIDS
* "Xtra Conditions = X-linked" (most disorders like color-blindness & hemophilia are on X)
* "He Can’t C" = Hemophilia & Color-blindness are X-linked
* "Only Guys Grow Hairy Ears" = Y-linked traits like hypertrichosis only appear in males
* "XX = She, XY = He" to remember female vs male chromosomes
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🎯 STRATEGIC TIPS
* Only females can be carriers of X-linked traits.
* Males are affected if they inherit just one X with a disorder (no second X to mask it).
* Use Punnett squares to easily determine offspring genotypes and phenotypes.
* Y-linked = passed father to son only.
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🧪 II. QUIZ BEE FORMAT QUESTIONS
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A. IDENTIFICATION
1. Trait caused by inability to distinguish certain colors. → _______________
2. X-linked disorder affecting blood clotting. → _______________
3. The sex chromosome found only in males. → _______________
4. Trait expressed only in males due to a gene on the Y chromosome. → _______________
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B. MULTIPLE CHOICE
1. What is the genotype of a color-blind male?
A. XᶜXᶜ
B. XᶜY
C. XᴴY
D. XᴴXᴴ
Answer: B
2. Which of the following is a Y-linked trait?
A. Color-blindness
B. Hemophilia
C. Hypertrichosis
D. Down syndrome
Answer: C
3. What percentage of children from a carrier mother (XᴴXʰ) and normal father (XᴴY) will have hemophilia?
A. 0%
B. 25%
C. 50%
D. 75%
Answer: B (only sons may have hemophilia: 25% total)
4. A color-blind man (XᶜY) marries a carrier woman (XᴄX). What percent of their sons will be color-blind?
A. 0%
B. 25%
C. 50%
D. 100%
Answer: C
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C. TRUE OR FALSE
1. Only females can be carriers of X-linked traits. → True
2. Y-linked traits can be passed from mothers to sons. → False
3. Color-blind females are more common than color-blind males. → False
4. A carrier mother has a 50% chance of passing the X-linked gene to her child. → True
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D. SITUATIONAL (ANALYSIS)
Example 1: A color-blind man marries a carrier woman. What are the possible genotypes and phenotypes of their children?
* Genotypes:
Male: XᶜY or XY
Female: XᶜX or XᶜXᶜ
* Phenotypes:
* 25% Normal Male
* 25% Color-blind Male
* 25% Carrier Female
* 25% Color-blind Female
Quick Rule: Dad gives Y to sons, X to daughters. Mom gives either Xᴴ or Xʰ to any child.
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🧾 QUICK REFERENCE TABLE
Cross
% Affected Sons
% Affected Daughters
% Carrier Daughters
XʰX × XY
25%
0%
25%
XʰX × XʰY
50%
25%
25%
XʰXʰ × XY
50%
100%
0%
XX × XʰY
50%
0%
0%
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🔍 PEDIGREE CHART NOTES
* Square = Male, Circle = Female
* Shaded = Affected
* Half-shaded circle = Carrier female
* Helps track inheritance through generations.
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QUIZ BEE REVIEWER: EPISTASIS, EXTRA-NUCLEAR INHERITANCE, MULTIPLE GENES
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📘 I. KEY CONCEPTS SUMMARY
🔹 1. Epistasis
* One gene masks or suppresses the expression of another gene.
* Epistatic gene = gene that does the masking
* Hypostatic gene = gene that gets masked
✅ Example: Llama Coat Color
* Gene B/b: B = black, b = brown
* Gene C/c: C = pigment deposited, c = no pigment (white coat)
* If cc, the llama is always white, regardless of B gene.
🔹 2. Extra-Nuclear Inheritance (Cytoplasmic Inheritance)
* Traits not controlled by nuclear DNA, but by DNA in organelles:
* Mitochondria (animals/plants)
* Chloroplasts (plants only)
* Inherited maternally via the egg cytoplasm
✅ Examples:
1. Four-o’Clock Plant Leaves: Leaf color depends on mother's branch (chloroplast DNA).
2. Human Mitochondrial Disorders:
* LHON (Leber’s Hereditary Optic Neuropathy) – vision loss
* MELAS – muscle and neurological issues
3. Petite Yeast Mutation – slow growth from mitochondrial mutation
🔹 3. Polygenic Traits / Multiple Genes
* Traits influenced by 2 or more genes, each contributing small additive effects
* Show continuous variation (not just dominant/recessive)
✅ Examples:
* Human Skin Color – more dominant alleles = darker skin
* Human Height – more capital alleles (A, B, C) = taller
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🧠 MNEMONICS / MEMORY AIDS
* “Epi = Exits the expression” – Epistatic gene masks the other.
* “MAMA MITO” – Mitochondria = Maternal Inheritance
* “Poly = Plenty” – Polygenic traits involve many genes
* “C before B” in Llama – C gene (Color deposit) must work before B gene (Black/Brown)
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🧾 QUICK REFERENCE TABLE
Concept
Description
Key Feature
Epistasis
Gene interaction where one masks another
Epistatic masks hypostatic
Extra-nuclear
Genes from mitochondria/chloroplasts
Maternal inheritance
Polygenic
Traits controlled by many genes
Continuous variation
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🎯 STRATEGIC TIPS
* In epistasis, always check which gene masks the other first.
* For extra-nuclear, always trace maternal line.
* For polygenic traits, more capital letters = more expression (tall, dark, etc.).
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🧪 II. QUIZ BEE FORMAT QUESTIONS
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A. IDENTIFICATION
1. The gene that suppresses the effect of another gene. → _______________
2. Genetic inheritance passed through organelles like mitochondria. → _______________
3. Trait influenced by many genes with additive effects. → _______________
4. A mitochondrial disorder that affects eyesight. → _______________
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B. MULTIPLE CHOICE
1. Which of the following describes an epistatic gene?
A. A gene hidden by another
B. A gene that makes protein
C. A gene that masks another gene’s expression
D. A recessive trait
✅ Answer: C
2. Which of these is not inherited through the nucleus?
A. Eye color
B. LHON
C. Height
D. Blood type
✅ Answer: B
3. In llama coat color, which gene is epistatic?
A. B
B. b
C. C
D. c
✅ Answer: C
4. What determines the leaf color of four-o’ clock plants?
A. Father’s DNA
B. Nuclear DNA
C. Maternal chloroplast DNA
D. Amount of sunlight
✅ Answer: C
5. A person inherits AABBcc alleles for height. What will their height most likely be?
A. Very short
B. Medium
C. Tall
D. Cannot be determined
✅ Answer: C
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C. TRUE OR FALSE
1. Only fathers can pass on mitochondrial traits. → False
2. Polygenic traits follow Mendelian ratios. → False
3. Epistasis involves multiple genes interacting. → True
4. Mitochondrial mutations affect energy production. → True
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D. ANALYSIS / SITUATION QUESTIONS
1. Epistasis Example
In mice, black coat (B) is dominant over brown (b), but a separate gene C allows color expression. If mouse is cc, it's white.
* Q: What is the phenotype of a Bbcc mouse?
→ White (because cc blocks pigment)
2. Extra-nuclear Inheritance Example
A mother with MELAS syndrome has children.
* Q: Which children can inherit the disorder?
→ All children (maternal inheritance)
3. Polygenic Example
Child has 4 dominant alleles for height.
* Q: Will the child be taller than someone with 2 dominant alleles?
→ Yes (more dominant = taller)
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