UPCAT Biology — Genetics & HeredityRevision Notes
Revision notes for UPCAT Biology Genetics & Heredity — designed for time-pressed reviewers. These notes skip the basics and focus on what University of the Philippines consistently tests, so you spend your revision hours on the content most likely to appear on exam day.
Exam context
The University of the Philippines College Admission Test is conducted by University of the Philippines and is scheduled for Mid-2026 (announced by UP Admissions). The Biology subtest is marked as "Core" in the official pattern, and Genetics & Heredity appears in position 6th of 7 in the UPCAT Biology review rotation. Passing mark: UPG ≤ 2.2 typical. Recent UPCAT 2026 papers have drawn roughly 20 questions from this subject.
Genetics & Heredity - Revision notes
Genetics is the study of how traits are passed from parents to their offspring, while heredity refers to the actual passing of genetic factors from one generation to the next. This chapter covers the fundamental principles established by Gregor Mendel, modern molecular genetics, and advanced inheritance patterns that are crucial for understanding how life perpetuates its characteristics. These concepts form the foundation of biotechnology, genetic engineering, and medical genetics - all important topics in Philippine college entrance examinations.
Sections
Formulas
Example
Pure breeding yellow peas (YY) × green peas (yy) → All yellow F1 (Yy) → F2 ratio 3:1 yellow:green
Formula
P1 × P1 → F1 → F1 × F1 → F2
Variables
P1 = Parental generation, F1 = First filial generation, F2 = Second filial generation
Application
Used to track inheritance patterns across generations in genetic crosses
Exam Tips
- Always define your symbols before solving genetics problems (e.g., Y = yellow, y = green)
- Draw Punnett squares systematically - label gametes first, then fill in combinations
- Check your ratios - they should match expected Mendelian ratios for simple crosses
Key Points
- A gene is a section of DNA that carries information for constructing a protein or part of a protein
- An allele is a variant form of a gene that determines specific traits
- Genotype refers to the genetic composition (allelic makeup) of an organism
- Phenotype is the observable trait expressed by the genotype
- DNA is composed of nucleotides containing nitrogenous bases (A, T, G, C), sugar backbone, and phosphate groups
- Pyrimidines include cytosine, thymine, and uracil; Purines include adenine and guanine
- Dominant alleles mask the expression of recessive alleles in heterozygous conditions
- Homozygous organisms have identical alleles for a trait, while heterozygous organisms have different alleles
Definitions
Term
Gene
Definition
A section of DNA that codes for a specific protein or trait
Importance
Fundamental unit of heredity that determines all inherited characteristics
Term
Allele
Definition
Different versions of the same gene that can produce variations in inherited traits
Importance
Explains genetic diversity and why offspring differ from parents and siblings
Term
Phenotype
Definition
The observable physical or biochemical characteristics of an organism
Importance
What we actually see or measure, resulting from the interaction of genotype and environment
Term
Genotype
Definition
The genetic makeup of an organism, specifically the allele combinations
Importance
Determines the potential traits an organism can express and pass to offspring
Section Title
Basic Genetics Concepts and Terminology
Common Mistakes
- Confusing genes with alleles - remember genes are the location, alleles are the variants
- Mixing up genotype and phenotype - genotype is genetic code, phenotype is what you observe
- Assuming dominant traits are more common - dominance refers to expression, not frequency
Formulas
Example
Yy × Yy → 3 yellow : 1 green pea seeds
Formula
Monohybrid F2 ratio = 3:1 (dominant:recessive)
Variables
3 = probability of dominant phenotype, 1 = probability of recessive phenotype
Application
Predicting outcomes when crossing two heterozygous individuals for one trait
Example
YyRr × YyRr → 9 yellow round : 3 yellow wrinkled : 3 green round : 1 green wrinkled
Formula
Dihybrid F2 ratio = 9:3:3:1
Variables
9 = both dominant, 3 = first dominant/second recessive, 3 = first recessive/second dominant, 1 = both recessive
Application
Predicting outcomes when crossing individuals heterozygous for two independent traits
Exam Tips
- For dihybrid crosses, use FOIL method to determine gamete types (First, Outer, Inner, Last)
- Always verify your Punnett square totals match expected ratios
- Practice identifying parental genotypes from offspring ratios
Key Points
- Law of Segregation: Each parent contributes one allele for each trait to offspring; allele pairs separate during gamete formation
- Law of Independent Assortment: Different genes are inherited independently of each other
- Law of Dominance: In heterozygous conditions, the dominant allele is expressed over the recessive
- Monohybrid crosses examine inheritance of a single trait (3:1 phenotypic ratio in F2)
- Dihybrid crosses examine two traits simultaneously (9:3:3:1 ratio in F2 for independent traits)
- Test crosses help determine unknown genotypes by crossing with homozygous recessive individuals
- Punnett squares predict probability of offspring genotypes and phenotypes
Definitions
Term
Law of Segregation
Definition
Allele pairs separate during gamete formation, and random fertilization restores pairs in offspring
Importance
Explains why offspring can show traits not seen in parents and forms basis of genetic inheritance
Term
Law of Independent Assortment
Definition
Genes for different traits are inherited independently, creating new combinations
Importance
Explains genetic recombination and why siblings can have very different trait combinations
Term
Monohybrid Cross
Definition
A genetic cross focusing on the inheritance pattern of a single trait
Importance
Simplest way to understand basic inheritance patterns and dominance relationships
Term
Dihybrid Cross
Definition
A genetic cross examining the simultaneous inheritance of two different traits
Importance
Demonstrates independent assortment and helps predict complex inheritance patterns
Section Title
Mendelian Genetics and Laws of Inheritance
Common Mistakes
- Forgetting to separate alleles when writing gamete genotypes
- Incorrectly applying independent assortment to linked genes
- Confusing F1 and F2 generation ratios - F1 is uniform, F2 shows segregation
Formulas
Example
Color blindness inheritance shows this pattern
Formula
Sex-linked recessive inheritance: XᴿXʳ × XᴿY → 1/2 carrier females, 1/4 normal females, 1/4 affected males
Variables
Xᴿ = normal allele, Xʳ = recessive allele, Y = male sex chromosome
Application
Predicting inheritance patterns for X-linked recessive disorders
Exam Tips
- For sex-linked problems, always show the sex chromosomes (X and Y) with alleles
- In multiple allele problems, remember individuals still only have two alleles
- Look for clues in problem wording: 'blended' suggests incomplete dominance, 'both present' suggests codominance
Key Points
- Incomplete Dominance: Neither allele is completely dominant; phenotype is a blend of both parents
- Codominance: Both alleles are fully expressed simultaneously in the phenotype
- Multiple Allelism: More than two alleles exist for a single gene in a population (e.g., ABO blood groups)
- Sex-linked inheritance: Traits carried on sex chromosomes show different inheritance patterns between males and females
- X-linked recessive traits are more common in males because they only need one copy
- Polygenic inheritance involves multiple genes contributing to a single trait
- Environmental factors can influence gene expression (phenotypic plasticity)
Definitions
Term
Incomplete Dominance
Definition
Neither allele is completely dominant; heterozygotes show an intermediate phenotype
Importance
Explains traits like flower color in snapdragons where red × white = pink
Term
Codominance
Definition
Both alleles are fully expressed simultaneously in heterozygotes
Importance
Explains ABO blood types where both A and B antigens can be present
Term
Multiple Allelism
Definition
The existence of more than two alleles for a single gene in a population
Importance
Increases genetic diversity and explains complex inheritance patterns like blood types
Term
Sex-linked Inheritance
Definition
Traits controlled by genes located on sex chromosomes, showing different inheritance patterns in males vs females
Importance
Explains why certain disorders are more common in one sex than the other
Section Title
Non-Mendelian Genetics
Common Mistakes
- Confusing incomplete dominance with codominance - blending vs. both traits visible
- Assuming sex-linked always means X-linked - Y-linked traits also exist
- Forgetting that males are more affected by X-linked recessive disorders
Formulas
Example
One chromosome becomes two identical sister chromatids joined at centromere
Formula
DNA Replication: Parental DNA → 2 identical DNA molecules
Variables
Each new molecule = 1 original strand + 1 newly synthesized strand
Application
Understanding how genetic information is copied before cell division
Exam Tips
- Remember the base pairing rules: A-T (or A-U in RNA) and G-C
- For transcription problems, the RNA sequence is complementary to the DNA template strand
- Frameshift mutations are usually more severe than point mutations
Key Points
- DNA structure: double helix with complementary base pairing (A-T, G-C)
- DNA replication is semiconservative - each new molecule contains one old and one new strand
- Central Dogma: DNA → RNA → Protein (replication → transcription → translation)
- Transcription occurs in the nucleus, producing mRNA from DNA template
- Translation occurs at ribosomes, using mRNA to synthesize proteins
- RNA differs from DNA: single-stranded, contains uracil instead of thymine, has ribose sugar
- Mutations can be substitutions, insertions, deletions, or frameshifts
- Genetic code is universal and redundant (multiple codons for same amino acid)
Definitions
Term
Central Dogma
Definition
The flow of genetic information from DNA to RNA to proteins
Importance
Fundamental principle explaining how genes control cellular functions and traits
Term
Transcription
Definition
The process of copying genetic information from DNA to mRNA
Importance
First step in gene expression, allows genetic information to leave the nucleus
Term
Translation
Definition
The process of using mRNA to synthesize proteins at ribosomes
Importance
Final step converting genetic code into functional proteins that determine traits
Term
Mutation
Definition
Changes in DNA sequence that can alter protein structure and function
Importance
Source of genetic variation and can cause genetic disorders or evolutionary advantages
Section Title
Molecular Basis of Heredity
Common Mistakes
- Confusing transcription and translation - transcription makes RNA, translation makes protein
- Using thymine in RNA sequences - RNA uses uracil instead of thymine
- Forgetting that DNA replication is semiconservative
Exam Tips
- Know the basic steps of genetic engineering: isolate gene → insert into vector → transform organism
- Understand both benefits and risks of genetic technologies
- Be familiar with current applications in Philippine agriculture and medicine
Key Points
- Genetic engineering involves manipulating DNA to create desired traits
- Recombinant DNA technology combines DNA from different sources
- GMOs (Genetically Modified Organisms) carry artificially introduced genes
- Gene therapy uses modified viruses to deliver normal genes to treat genetic diseases
- DNA sequencing determines the exact order of nucleotides in DNA
- Human Genome Project mapped all human genes (about 21,000 genes)
- PCR (Polymerase Chain Reaction) amplifies specific DNA sequences
- Biotechnology applications include medicine, agriculture, and forensics
Definitions
Term
Genetic Engineering
Definition
The direct manipulation of an organism's genes using biotechnology techniques
Importance
Allows creation of organisms with beneficial traits for medicine, agriculture, and research
Term
Recombinant DNA
Definition
DNA molecules formed by combining genetic material from different sources
Importance
Foundation of genetic engineering and biotechnology applications
Term
GMO
Definition
Genetically Modified Organism that has had its genetic material altered using genetic engineering techniques
Importance
Important in agriculture for improved crops and in medicine for producing human proteins
Term
Gene Therapy
Definition
Medical technique involving the introduction of genetic material into patient cells to treat disease
Importance
Potential treatment for genetic disorders and some cancers
Section Title
Applications: Genetic Engineering and Biotechnology
Common Mistakes
- Confusing genetic engineering with natural selection - one is artificial, one is natural
- Thinking all GMOs are harmful - many provide important benefits
- Not understanding the ethical considerations surrounding genetic technologies
Connections
- Genetics connects to Evolution - mutations provide variation for natural selection
- Molecular genetics relates to Biochemistry - genes code for enzymes that control metabolic pathways
- Inheritance patterns connect to Mathematics - probability calculations predict offspring ratios
- Genetic engineering links to Environmental Science - GMO crops affect ecosystems
- Medical genetics connects to Health Science - understanding genetic disorders and treatments
- Population genetics relates to Ecology - allele frequencies change in populations over time
Exam Strategy
Focus on problem-solving skills for genetics crosses. Practice drawing Punnett squares systematically, always define your symbols clearly, and memorize key ratios (3:1 for monohybrid, 9:3:3:1 for dihybrid). For molecular genetics, understand the flow from DNA to protein and be able to write complementary sequences. Know the differences between Mendelian and non-Mendelian inheritance patterns. For biotechnology, understand basic techniques and their applications. Practice interpreting pedigree charts and solving inheritance problems step by step.
Quick Review Questions
What is the difference between genotype and phenotype?
For example, Yy is a genotype while yellow seed color is the corresponding phenotype
What would be the expected ratio in F2 generation of a monohybrid cross between two heterozygotes?
Yy × Yy produces YY, Yy, Yy, yy genotypes, giving 3 dominant : 1 recessive phenotype
How does incomplete dominance differ from codominance?
Red × white flowers = pink (incomplete) vs AB blood type showing both A and B antigens (codominance)
What is the Central Dogma of molecular biology?
Shows the flow of genetic information from storage in DNA to functional proteins
Why are X-linked recessive traits more common in males?
Females need two recessive alleles (one on each X) while males need only one
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