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Genetics and Evolution: SPI Biology

Genetics and Evolution has 7 questions in the SPI bank, and one is from the 2022 paper: what therapeutic cloning rests on. Only two are EASY, three are MODERATE and two are HARD, the smallest share of EASY questions of any SPI Biology chapter. Most of the difficulty is names: a theory and its author, a title such as 'father of human genetics', a kind of cloning. The one calculation, a dihybrid cross, always comes back to the 9 : 3 : 3 : 1 ratio, so it is the surest mark here once the ratio is learnt.

The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.

SPI home All formulas on one page

Subtopic notes

Formula & revision sheet

1 formulas · 3 reference tables · 8 gotchas across all subtopics — the exam-eve cheat-sheet

Heredity and Mendel's Crosses

Formulas (1)

Monohybrid and dihybrid crosses · F2 ratios $\text{monohybrid } 3:1,\quad \text{dihybrid } 9:3:3:1,\quad \text{number in a class} = \frac{\text{class share}}{16} \times \text{total}$

Reference tables (1)

Names in genetics and cloning6 rows

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

Watch out for (4)

Using 9/16 for a mixed class
→ Monohybrid and dihybrid crosses
Reading a capital letter as a fixed colour
→ Monohybrid and dihybrid crosses
Mendel for human genetics
→ Names in genetics and cloning
Therapeutic cloning makes a whole animal
→ Names in genetics and cloning

Evolution and Its Evidence

Reference tables (2)

Theories of evolution and their authors4 rows

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 organs2 rows

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.

Watch out for (4)

Darwin for every evolution question
→ Theories of evolution and their authors
Mendel as an evolution theorist
→ Theories of evolution and their authors
Calling any two wings homologous
→ Fossils, homologous and analogous organs
Thinking depth says nothing about age
→ Fossils, homologous and analogous organs

Question weightage by concept

4 concepts · 7 questions — where the marks actually sit, so you know what to drill first

Heredity and Mendel's Crosses3 questions · 43%

Concept	Qs	Share
Names in genetics and cloning	2	29%
Monohybrid and dihybrid crosses	1	14%

Evolution and Its Evidence4 questions · 57%

Concept	Qs	Share
Theories of evolution and their authors	2	29%
Fossils, homologous and analogous organs	2	29%

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