Applicable for A-Level, IB, DSE, AP-Level Exams

Biological Molecules    Cell Structure    Cell Transport    Immunology    Exchange    Mass Transport    DNA, Genes & Protein Synthesis    Genetic Diversity    Biodiversity    Photosynthesis    Respiration    Energy & Ecosystems    Stimuli and Response    Nervous Coordination & Muscles    Homeostasis    Inheritance    Populations & Evolution    Ecosystems    Gene Expression    Recombinant DNA Technology   


Genotype is the genetic constitution of an organism. Phenotype is the expression of this genetic constitution and its interaction with the environment. A Punnett Square allows for phenotypic ratios to be worked out.

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Dihybrid Inheritance

Dihybrid inheritance is the inheritance of 2 characters determined by 2 different genes located on different chromosomes. A dihybrid cross investigates the genotypic and phenotypic ratios of 2 alleles between the cross of 2 parents.

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There are 2 types of linkage: autosomal linkage (on non-sex chromosomes) or sex-linkage (on sex-chromosomes).

Aytosomal linkage is where 2 or more genes are carried on the same autosome. Linkage would cause the phenotypic ratio to be completely different than expected. Within sex-linkage, the production from a specific gene is carried either by the X or Y chromosome.

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Epistasis is where one gene masks the expression of another gene. Alleles will be recessive epistatic or dominant epistatic.

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