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Summary OCR A-Level Biology 6.2.4-7 Patterns of Inheritanc
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Revision summary of key knowledge from OCR A-Level Biology 6.2.4-7 Patterns of Inheritance.
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Other Patterns ofInheritance
Multiple Alleles
When there are three or more alleles in the gene pool at a specific gene locus
Involves dominance hierarchies and can involve codominance
Codominance is where both alleles present in the genotype are expressed in the
phenotype
Example: Blood Groups
o IAIA/O = group A
o IBIB/O = group B
o IAIB = group AB
o IOIO = group O
o A and B are codominant, and O is recessive
Example: Sickle Cell Anaemia
o HbN = normal allele Hb5 = mutated allele
o Heterozygous individuals have both normal and sickle-shaped RBCs but can
survive normally with half the amount of functioning RBCs
o Heterozygous individuals are immune to malaria so this can be an advantage and
is more common in areas with Anopheles mosquitos
Linkage
Sex Linkage – gene loci present on the sex chromosome
Usually more common in the sex with the XY chromosome pattern (males in humans)
since the Y chromosome is shorter
E.g. colour blindness, haemophilia
Autosomal Linkage – gene loci present on the same autosome (non-sex chromosome)
that are often inherited and expressed together
E.g. sweet pea colour and grain length
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