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Chapter 6

HMB265H1 Chapter Notes - Chapter 6: Hh Blood Group, Epistasis, Summer Squash

Human Biology
Course Code
Maria Papaconstantinou

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Lecture 6 - Textbook reading
Hartwell et al., 1st Can. edition, Chapter 2 (emphasis on pages 42-51) and Chapter 8
(emphasis on pages 253-255)
Extension to mendel for gene interactions
Most traits are regulated by two or more genes
Two genes can interact to determine one trait
Novel phenotypes resulting from gene interactions
Example: lentil coat colour
Tan x grey
9 brown: 3 tan: 1 grey: 1 green
Four colour phenotypes arise from four genotypic classes, with each class defined
in terms of presence or absence of dominant alleles
Both present
One present
The other presne
Neither present
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Complementary gene action
Example: pea flower colors
At least one dominant allele for each gene is necessary for the development
of purple color
9:7 ratio!!!
Complementary gene action:
it talks two enzyme catalyzing two reaction
Only A-N- active both enzymes → generate coloured
A-bb, aaB-, aabb do not have functional form or enzyme
7 comes from 3+3+1
Example: labrador retrievers
Coat color depends on allelic combination of two independently assorting
B black bb brown
E no effect, ee gold because it hides the effect of brown/black
Epistasis: a gene interaction in which the effects of an allele at one gene hide the
effect of alleles at another gene
The allele that is doing there is epistatic
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