MENDEL'S LAW OF HEREDITY. 



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MENDEL'S LAW OF HEREDITY. 

 By C. C. HuBST, F.L.S. 

 [Read before the Scientific Committee, on March 20th, 1906.] | 



Mendel experimented with seven pairs of pure bred " characters " in peas, 

 viz. yellow and green seeds (cotyledons), round and wrinkled seeds, purple 

 and white flowers, tall and dwarf stems, inflated and constricted pods, 

 green and yellow pods, axial and terminal flowers. In each pair, when 

 crossed, Mendel found the first-named character dominant over the other, 

 which he called recessive : e.g. yellow crossed with green gave seeds all 

 with yellow cotyledons. In this case yellow is dominant over green, which 

 is recessive. 



Mendelian dominance has recently been found to hold good in a large 

 number of characters in many species of plants and animals ; e.g. in my 

 own experiments I have found the following among many others (the 

 dominant character is named first) : — 



Peas : Round and wrinkled seeds ; yellow and green cotyledons. 



Siveet Peas : Tall and dwarf stems (Cupid) ; long and round pollen 

 grains. 



Primula : Palm and fern leaf ; thrum and pin-eyed. 

 Antirrhinum : Red and white flowers ; white and yellow flowers. 

 Tomato : Red and yellow flesh ; yellow and white skin of fruit. 

 Orchids : Spotted and striped flowers. 



Poultry : Rose and single comb ; white and black plumage. 



Babbits : Coloured and white coat ; short and angora coat. 



Horses : Bay and chestnut colour ; brown and chestnut colour. 



Recent experiments show that the phenomenon of complete dominance 

 is by no means universal. In many cases the dominance is incomplete, 

 distinct traces of the recessive character being visible in the crossbreds, 

 e.g. in my poultry experiments white x black plumage gave both clear 

 white and white ticked with black, the dominance of white being incom- 

 plete in the latter case. In some cases hybrid characters appear to be 

 intermediate between the parents, e.g. some characters in orchid hybrids. 



In a few cases the hybrid characters are like neither parent, but appear 

 to revert to an ancestral form, e.g. ' Black Knight ' sweet pea x * Pink 

 Cupid ' gave all wild purple crossbreds. In a few cases, again, the hybrid 

 characters are like neither parent, nor are they reversions, but give an 

 apparently new character, e.c/. the blue Andalusiiui fowl is a distinct hybrid 

 breed between a black and a splashed white, and never breeds true. In 

 nearly all the cases, however, so far as they have yet been investigated, 

 Mendel's law of segregation and purity is evident. It is, moreover, 

 evident that many of the so-called intermediate hybrids are really due to 

 the association of two distinct dominant characters each with an inde- 

 pendent Mendelian heredity. 



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