3bReproduction and Inheritance
Inheritance — Edexcel Linear - OL Revision Notes & Topical Questions
5 min read 7 parts Lesson 2 of 5 1 quiz
Lesson summary
Inheritance Edexcel O Level Linear Biology notes: understand that the genome is the entire DNA of an organism and that a gene is a section of a molecule of DNA that codes for a specific proteinGenes on the same chromosome tend to be inherited together.Mitochondria come from the e…
- Inheritance Edexcel O Level Linear Biology: what to do next
- Incomplete dominance
- Codominance
- Multiple alleles
- Sex-linked
- Linked genes
Section 1 of 7Process & sequence
1
Count recombinant offspring.
2
Divide by total offspring.
3
× 100 = recombination frequency.
4
1% = 1 map unit (centimorgan).
1
Genes far apart
2
More crossing over
3
Higher recombination frequency
Section 2 of 7Keep going
Inheritance Edexcel O Level Linear Biology: what to do next
These Inheritance Edexcel O Level Linear Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your Inheritance Edexcel O Level Linear Biology understanding with the practice questions below, then reread any Inheritance Edexcel O Level Linear Biology point you were unsure about before moving on.
2
Previous lesson: 3a Reproduction — Notes
3
Next lesson: 4a The organism in the environment — Notes
4
Course: Edexcel Linear - OL — all units
5
Official syllabus: Pearson Edexcel International GCSEs
Section 3 of 7Compare
| Pattern | Example | Heterozygote / cross result | Ratio | Deviation from Mendel | Note |
|---|---|---|---|---|---|
| Incomplete dominance | Snapdragon colour | Pink | 1 : 2 : 1 | Blended | — |
| Codominance | AB blood, roan cattle | Both traits | 1 : 2 : 1 | Both shown | — |
| Sex-linked | Hemophilia, colour blindness | Carrier females | Depends on sex | More males affected | X-linked |
| Linked genes | Genes on same chromosome | Parental types more common | Not 9:3:3:1 | Recombination frequency | Map units |
| Polygenic | Skin colour, height | Continuous range | Bell curve | Many genes | — |
| Mitochondrial | Some muscle diseases | All children of affected mother | — | Maternal only | — |
Section 4 of 7Key terms
Section 5 of 7Syllabus checklist
1
understand that the genome is the entire DNA of an organism and that a gene is a section of a molecule of DNA that codes for a specific protein
2
understand that the nucleus of a cell contains chromosomes on which genes are located
3
understand how genes exist in alternative forms called alleles which give rise to differences in inherited characteristics
4
understand the meaning of the terms
- dominant
- recessive
- homozygous
- heterozygous
- phenotype
- and genotype
5
understand that most phenotypic features are the result of polygenic inheritance rather than single genes
6
describe patterns of monohybrid inheritance using a genetic diagram
7
understand how to interpret family pedigrees
8
predict probabilities of outcomes from monohybrid crosses
9
understand how the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male
10
describe the determination of the sex of offspring at fertilisation, using a genetic diagram
11
understand how division of a diploid cell by mitosis produces two cells that contain identical sets of chromosomes
12
understand that mitosis occurs during growth, repair, cloning and asexual reproduction understand how division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes
13
understand how random fertilisation produces genetic variation of offspring
14
know that in human cells the diploid number of chromosomes is 46 and the haploid number is 23
15
understand that variation within a species can be genetic, environmental, or a combination of both
16
understand that mutation is a rare, random change in genetic material that can be inherited
17
explain Darwin's theory of evolution by natural selection
18
understand how resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lead to infections being difficult to control
Section 6 of 7Command terms
Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.
Section 7 of 7Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Incomplete dominance · Codominance · Multiple alleles · Sex-linked · Linked genes · Polygenic · Epistasis · Mitochondrial inheritance
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. eukaryotic/prokaryotic, enzyme–substrate complex, active site, complementary).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.
Marked practiceQuizzes for this lesson
Last updated:
\n