CHARACTERS KNOWN TO BE INHERITABLE 631 



Much study has been given to the inheritance of defects and 

 susceptibility to diseases. The following list probably is approxi- 

 mately correct. 



Dominant Character Recessive Character 



Two- jointed fingers Normal fingers 



Extra digit Normal number of digits 



Congenital cataract of eye Normal condition of eye 



Abnormally short limbs Normal limbs 



Hairless or toothless condition Normality 



Spotted hair coat Normality 



Cases where the defect is recessive to the normal condition are 

 much more difficult to find, but the following examples appear to 

 be well established, according to Guyer : 



Dominant Character Recessive Character 



Normal pigment Albino skin 



Normal intellect Feeble-mindedness 



Normal intellect Alcoholism (when based on feeble- 

 mindedness) 



Normality Susceptibility to cancer 



Normality Tendency to asthma or hay fever 



Normality Probable susceptibility to tuberculosis 



Normality Lack of muscular control 



Self-Testing Exercise t 



Chromosomes are the (1) of (2) characters. The 



fertilized egg contains (3) or . (4) from both parents. 



(5) are definite in number for each species of animal or 



parent. The triangle of life consists of (6), (7), 



and (8). Certain characteristics, such - as (9), 



(10), and (11), appear to be inherited according to 



Mendel's Laws. Dark skin is a (12) character, light skin a 



(13) character. One's heredity may be affected by the 



(14) from the endocrine glands. The size of giants and 



dwarfs appears to be determined by the size of the (15) gland. 



PROBLEM V. HOW ARE NEW VARIETIES OF PLANTS AND 

 ANIMALS PRODUCED 



Laboratory Exercise. To determine whether there is individual 

 variation in any one measurement of the members of a given class. 

 With a string carefully measure the length of your arm from the 

 finger 'tips to the elbow. Take measurements on back of hand. 



