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Lesson 2 of an A Level teaching resource, produced in conjunction with the Charles Darwin Trust, that uses Darwin's work on pigeon breeding and the work of contemporary scientists to explore genetics and evolution. This second lesson covers the topic of genetics. The accompanying teacher's notes can be found on our website at www.linnean.org/funkypigeons
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Funky Pigeons
Revealing the biology of inheritance and selection
Lesson 2Genetics
Picture courtesy John Ross: darwinspigeons.com
Parents Offspring?
Whose baby?
Images © Genetics Society of America. From Genetics September 1, 1922 vol. 7 no. 5 466-507 STUDIES ON INHERITANCE IN PIGEONS. IV. CHECKS AND BARS AND OTHER MODIFICATIONS OF BLACK by Sarah Van Hoosen Jones.
A Victorian Pigeon Club show (1853)
© Mary Evans Picture Library / Illustrated London News Ltd
“The laws governing inheritance are for the most part unknown…”
Charles Darwin On the Origin of Species
(5th Ed.), 1869
Inheritance
Sarah Van Hoosen Jones: The Petticoat Farmer
Courtesy Archives of Michigan
Pigeon colour/pattern phenotypes
Solid black
Chequered
Barred
Barless
© Genetics Society of America. From Genetics September 1, 1922 vol. 7 no. 5 466-507 STUDIES ON INHERITANCE IN PIGEONS. IV. CHECKS AND BARS AND OTHER MODIFICATIONS OF BLACK by Sarah Van Hoosen Jones.
Type 1 occulocutaneous albinism in mice caused by the gene TYR (tyrosinase)
Albinism
Picture by Aaron Logan (commons.wikimedia.org)
Human genetics and recessive epistasis
Unaffected “Carrier” Mother
Unaffected “Carrier”
Father
Unaffected 1 in 4 chance
Unaffected “Carrier” 2 in 4 chance
Affected 1 in 4 chance
MCR1 acts as a switch controlling whether eumelanin (brown/black) or phaeomelanin (red) are produced
The allele that causes red hair is recessive to the allele that causes brown and black hair.
The MCR1 gene and red hair
Picture by John Griffiths (commons.wikimedia.org)
TYR is epistatic to MCR1
Sex linked inheritance in humans
The female is the HETEROGAMETIC sex
Sex linked inheritance in birds
The male is the HOMOGAMETIC sex
Phenotypic ratios for crosses involving heterozygotes:
One allele a monohybrid cross – 3:1
Two alleles a dihybrid cross – 9:3:3:1
Dihybrid cross with recessive epistasis – 9:3:4
Dihybrid cross with dominant epistasis – 12:3:1
Summary
“…it will now be seen that when two birds belonging to distinct races are crossed, neither of which have, nor probably have had during many generations, a trace of blue in their plumage, or a trace of wing-bars and the other characteristic marks, they very frequently produce mongrel offspring of a blue colour, sometimes chequered, with black wing-bars, etc.; or if not of a blue colour…”
Charles DarwinThe variation of animals and plants under domestication, 1868
Darwin on genetics
