Key term
OCR A-Level Biology H420
Cell Structure
Biological Molecules
Nucleotides and Nucleic Acids
Enzymes
Biological Membranes
Cell Division, Cell Diversity and Cellular Organisation
Exchange Surfaces
Transport in Animals
Transport in Plants
Communicable Diseases, Disease Prevention and the Immune System
Biodiversity
Classification and Evolution
Communication and Homeostasis
Excretion as an Example of Homeostatic Control
Neuronal Communication
Hormonal Communication
Plant and Animal Responses
Topic overviewTropisms and plant responses to stress and herbivoryPlant hormones and their commercial usesThe nervous system and the brainReflex actions and the knee jerk reflexFight or flight and the control of heart rateThe structure of skeletal muscleThe neuromuscular junction and the sliding filament model
Photosynthesis
Respiration
Cellular Control
Patterns of Inheritance
Manipulating Genomes
Cloning and Biotechnology
Topic overviewNatural plant cloning and taking cuttingsMicropropagationAdvantages and disadvantages of plant cloningAnimal cloning: embryo twinning and nuclear transferAdvantages and disadvantages of animal cloningMicroorganisms in food productionAseptic techniqueFermentation and its conditionsThe microbial growth curveImmobilised enzymes
Ecosystems
Populations and Sustainability
Practical Skills and Mathematical Requirements
Patterns of Inheritance
Monogenic and dihybrid inheritance, sex linkage and epistasis
- 4 things to know
- Components 02 and 03
Overview
Monogenic and dihybrid crosses and the expected ratios, multiple alleles, codominance and sex linkage, and the modified ratios that reveal linkage and epistasis.
What you need to know
Answer each one before you reveal it.
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Key term
What is sex linkage?
Key term
Define codominance.
Key term
Define epistasis.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is monogenic inheritance?
Model answer
Monogenic inheritance is when a single gene controls a characteristic.
- 2
How can monogenic inheritance patterns be represented?
Model answer
Using genetic diagrams showing parental genotypes, gametes, and offspring genotype and phenotype ratios.
- 3
What phenotypic ratio is expected in the F₂ generation of a dihybrid cross when the two genes are unlinked?
Model answer
9:3:3:1
- 4
What does dihybrid inheritance involve?
Model answer
The inheritance of two genes controlling two different characteristics.
- 5
What are multiple alleles?
Model answer
Multiple alleles occur when a gene has more than two alleles in a population.
- 6
What is sex linkage?
Model answer
Sex linkage refers to genes located on sex chromosomes, typically the X chromosome, leading to different inheritance patterns in males and females.
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