630 IMPROVEMENT OF LIVING THINGS BY MAN 



Offspring are part of their ancestors. If you receive characters 

 from your parents and they received characters from their parents, 



wale <? 



female $ 



mother" 

 reproductive 



periocC of 

 gr-o^th! 



reduction 

 division 



y/M^ *- "f -?fsH\ 



The " mother " reproductive cells divide and one of the resulting 

 cells grows larger. During this period of growth each cell divides 

 in such a way that one half of the chromosomes goes to each of the 

 daughter (or resulting) cells. Each female cell gives rise to one 

 egg and three small cells. The egg has most of the yolk and is 

 generally the only one that will be fertilized. The large male cell 

 divides, and gives rise to four sperms, all the same size, and all 

 of which can function. Each sperm will contain one half the 

 number of chromosomes found in the large cell. One sperm 

 unites with the mature egg in the process of fertilization. 



then you must have 

 some of the char- 

 acters of the grand- 

 parents. As a 

 matter of fact each 

 of us does have 

 some traits or line- 

 aments which can 

 be traced back to 

 a grandfather or 

 grandmother. In- 

 deed, as far back 

 as we are able to 

 go, ancestors have 

 contributed some- 

 thing. 



agram ? What seems to be the reason for the 



Practical Exercise 

 13. Study the dia- 

 gram carefully. How 

 can you account for 

 the different combina- 

 tions in the four ferti- 

 lized eggs shown at 

 _ the bottom of the di- 

 reduction " division? 



Turn over to the diagram on page 628. Make a similar diagram for your 

 workbook that will show how a chromosome in an egg and a sperm cell might 

 contain genes. 



Characters known to be inheritable. The following table 

 indicates some of the characters in man that have been proved to 

 be inheritable according to the laws of Mendel. 



Dominant Character 

 Black or brown eye 

 Pigmented iris 

 Dark skin 

 Curly hair 

 Dark hair 



Congenital white lock 

 Beaded hair 

 Nervous temperameot 



Recessive Character 

 Blue or gray eye 

 No pigment in iris 

 Light skin 

 Straight hair 

 Light hair 

 Normal hair 

 Straight hair 

 Phlegmatic temperament 



