SPI Biology · Formula sheet
Genetics and Evolution formulas
1 formula, 3 reference tables and 8 common traps for SPI Biology Genetics and Evolution, grouped by subtopic.
Heredity and Mendel's Crosses
Learn this subtopic in the notesMonohybrid and dihybrid crosses
F2 ratios
Names in genetics and cloning
| Scientist | Known for |
|---|---|
| Gregor Mendel | Father of genetics |
| Sir Archibald Garrod | Father of human genetics Mendel is the father of genetics; Garrod of human genetics. |
| T H Morgan | Genes on chromosomes, fruit flies |
| Har Gobind Khorana | The genetic code |
| Watson and Crick | Double helix of DNA |
| Ian Wilmut | Dolly, the first cloned mammal |
Common traps
Using 9/16 for a mixed class
A class with one dominant and one recessive trait is one of the two '3' classes, so its share is 3/16. Only the class with both dominant traits is 9/16.
Reading a capital letter as a fixed colour
Which trait is dominant is given in the question. If it says green is dominant over yellow, then G is green, even though Mendel's own peas had yellow dominant.
Mendel for human genetics
Mendel worked on peas and is the father of genetics as a whole. The father of human genetics is Sir Archibald Garrod.
Therapeutic cloning makes a whole animal
Reproductive cloning makes a whole animal, like Dolly. Therapeutic cloning stops at stem cells, which are grown into the tissue a patient needs.
Evolution and Its Evidence
Learn this subtopic in the notesTheories of evolution and their authors
| Scientist | Theory |
|---|---|
| Lamarck | Inheritance of acquired characters |
| Charles Darwin | Natural selection Darwin's book: On the Origin of Species (1859). |
| August Weismann | Germplasm theory |
| Hugo de Vries | Mutation theory |
A change a body acquires in life (a strong arm, a cut tail) is not passed on: Weismann's point against Lamarck.
Fossils, homologous and analogous organs
| Type | Structure | Job | Example |
|---|---|---|---|
| Homologous | Same | Different | Forelimbs of cow, duck, lizard, human Homologous: same build, different use. |
| Analogous | Different | Same | Wings of butterfly and bird |
Homologous organs point to a common ancestor; analogous organs only to a common need.
Common traps
Darwin for every evolution question
Darwin gave natural selection only. The germplasm theory is Weismann's, the mutation theory de Vries's and acquired characters Lamarck's.
Mendel as an evolution theorist
Mendel worked out how traits are inherited. He gave no theory of how species change.
Calling any two wings homologous
Wings do the same job, so two wings are analogous: a butterfly's and a bird's are built from different parts. Homologous organs are the ones with the same build but different jobs, such as forelimbs.
Thinking depth says nothing about age
Rock layers pile up over time, so the deeper the layer, the older the fossil in it.