Choose an exam and explore concepts through visual explanations, topic maps and revision checks. Open the full chapter notes whenever you need more detail.
THE VISUAL LEARNING STUDIO
See the idea. Understand the connection.
35 visual explanations across 29 chapters, with topic maps throughout the library.
The chapter index will grow as additional notes are prepared. Chapters shown here are a learning collection, not a claim that the entire exam syllabus is complete.
SEE IT. CONNECT IT. EXPLAIN IT.
Understand the chapter visually
1 visual explanation · Study the connections, then test yourself.
Use Recall mode to hide explanations; tap or focus a card to reveal one. Expand any diagram for a larger view.
WORK THROUGH THE CROSS
A monohybrid cross: Aa × Aa
Parental gametes: A or a, each with probability ½
×
A · ½
a · ½
A · ½
AA ¼
Aa ¼
a · ½
Aa ¼
aa ¼
1
AA
One of four equally likely genotype combinations.
2
Aa
Two of four combinations are heterozygous.
3
aa
One of four combinations is homozygous recessive.
The connection With equal segregation, random fertilisation and complete dominance, the expected genotype ratio is 1:2:1 and phenotype ratio is 3:1.
Exam trap A probability ratio is not an exact quota for every small family. Incomplete dominance changes the phenotype ratio.
Under complete dominance, what is the probability of the recessive phenotype?
One quarter, because only aa expresses the recessive phenotype under these assumptions.
Study the expanded notes and the credited detailed textbook lessons. The current chapter index covers core topics; it is not a claim of exhaustive coverage of every examination syllabus. Check the official syllabus and primary references.
Genetics — lesson overview
Information and alleles
A gene is a functional hereditary unit associated with a DNA sequence and its biological expression; alleles are alternative forms at a locus.
Genotype describes genetic constitution in the relevant context; phenotype is the observable expression influenced by genotype and environment.
Dominant does not mean common, better or universally stronger; it describes a particular pattern of expression in heterozygotes.
Mendelian reasoning
In a simple monohybrid cross of heterozygotes Aa × Aa, the genotype ratio is 1 AA : 2 Aa : 1 aa under the standard assumptions.
A 3:1 phenotypic ratio follows only with complete dominance and the other relevant conditions. Different inheritance patterns produce other outcomes.
Probability describes expected proportions over many events; four offspring are not guaranteed to occur in exactly the expected ratio.
Beyond the simplest model
Incomplete dominance, codominance, linkage, multiple genes and environmental effects show why every trait cannot be explained by one dominant/recessive pair.
Linked loci can show non-independent inheritance, while crossing over can generate recombinant combinations.
Mutations change genetic material; selection changes the relative representation of inherited variation across generations. These are different processes.
