IB MYP 4-5 Biology-Inheritance and Variation- Study Notes - New Syllabus
IB MYP 4-5 Biology-Inheritance and Variation- Study Notes – New syllabus
IB MYP 4-5 Biology-Inheritance and Variation- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Mendelian genetics
- Dominant and recessive traits
- Continuous and discontinuous variation
Mendelian Genetics
Who Was Gregor Mendel?
Mendel was an Austrian monk and scientist who experimented with pea plants to understand inheritance. He is known as the Father of Genetics.
What Did Mendel Discover?
- Traits are controlled by “factors” (now called genes)
- Each individual has two copies of each gene one from each parent
- Genes can be dominant or recessive
Mendel’s Two Key Laws
1. Law of Segregation: Each parent has two alleles, but only one is passed on during gamete formation (meiosis).
2. Law of Independent Assortment: Inheritance of one trait doesn’t affect another (traits assort independently).
Key Terms to Know
| Term | Meaning |
|---|---|
| Gene | Segment of DNA controlling a trait |
| Allele | A version of a gene (e.g., T or t) |
| Dominant allele | Always shows its effect (T) |
| Recessive allele | Only shows if both copies are recessive (t) |
| Homozygous | Two same alleles (TT or tt) |
| Heterozygous | Two different alleles (Tt) |
| Genotype | Genetic makeup (e.g., Tt) |
| Phenotype | Visible trait (e.g., tall plant) |
Example: Monohybrid Cross
Parent Generation: TT (tall) × tt (short)
F1 Generation: All Tt – All tall
F2 Generation (Tt × Tt):
| Combination | Genotype | Phenotype |
|---|---|---|
| TT | Homozygous tall | Tall |
| Tt | Heterozygous | Tall |
| tt | Homozygous short | Short |
Why Mendelian Genetics Is Important
- Explains inheritance patterns in families
- Forms the base of genetics and genetic testing
- Helps in predicting genetic disorders
- Supports understanding of evolution and DNA mutations
Dominant and Recessive Traits
What Are Traits?
A trait is a specific characteristic of an organism – like eye color, height, or blood type. Traits are controlled by genes, which exist in different versions called alleles.
You inherit one allele from each parent, so you always have two alleles for each gene.
What Are Dominant and Recessive Traits?
Dominant Trait: Shows up even if only one copy of the dominant allele is present.
Example: If tall (T) is dominant, then both TT and Tt plants will be tall.
Recessive Trait: Only shows if both alleles are recessive.
Example: A plant with genotype tt will be short.
Genotype vs Phenotype
| Term | Meaning |
|---|---|
| Genotype | The combination of alleles (e.g., TT, Tt, or tt) |
| Phenotype | The visible trait (e.g., tall or short) |
Example: Height in Pea Plants
| Genotype | Alleles | Phenotype (Trait) |
|---|---|---|
| TT | Dominant + Dominant | Tall |
| Tt | Dominant + Recessive | Tall |
| tt | Recessive + Recessive | Short |
Key Points to Remember
- Dominant traits need only one dominant allele to be expressed
- Recessive traits need two recessive alleles to be seen
- Dominant doesn’t mean “better” – just more likely to appear
- You can carry a recessive gene without showing it (like Tt)
Real-Life Examples
| Trait | Dominant | Recessive |
|---|---|---|
| Earlobe type | Free (F) | Attached (f) |
| Dimples | Present (D) | Absent (d) |
| Tongue rolling | Can roll (R) | Can’t roll (r) |
| Eye color | Brown (B) | Blue (b) |
| Widow’s peak | Present (W) | Straight hairline (w) |
Why Does It Matter?
- Helps predict how traits are passed from parents to children
- Used to study and prevent inherited disorders
- Explains why family members share or differ in traits
- Builds understanding of evolution and diversity
Continuous and Discontinuous Variation
What Is Variation?
Variation means the differences between individuals of the same species. It can be:
- Genetic: Inherited from parents
- Environmental: Caused by surroundings
- Both: Many traits are influenced by genes and environment
Two Main Types of Variation
1. Continuous Variation
- Shows a full range of values (not fixed groups)
- Controlled by many genes (polygenic)
- Often influenced by the environment
- Traits vary gradually between individuals
Examples: Height, skin tone, weight, hand span, leaf length
| Feature | Description |
|---|---|
| Range of values? | Yes (no fixed categories) |
| Controlled by | Many genes + environment |
| Graph shape | Bell curve |
| Examples | Height, weight, skin color |
2. Discontinuous Variation
- Traits fall into clear categories
- Controlled by one or a few genes
- Not greatly affected by environment
- No in-betweens – you either have the trait or not
Examples: Blood group, tongue rolling, eye color, earlobe type
| Feature | Description |
|---|---|
| Range of values? | No (fixed categories) |
| Controlled by | One or few genes |
| Graph shape | Bar chart |
| Examples | Blood group, tongue rolling |
Why Does Variation Matter?
- Drives evolution and natural selection
- Allows survival in different environments
- Explains differences within a population
- Important in breeding, healthcare, and conservation
Continuous variation = smooth, measurable traits (e.g., height).
Discontinuous variation = distinct traits (e.g., blood group).
Both types are key to understanding diversity, inheritance, and evolution.