PROBLEM 2. Differ e7ices Between Barents and Offspring ^nn 



and white in one pair of chromosomes and tall and short in a second pair. 

 Let a red bean represent the chromosome with a gene for redness; a white 

 bean its mate. Cut small squares of paper of the same size and write T on 

 half of them and s on the others. Put the paper and beans into one jar. 

 As this jar "makes" gametes you must be sure that each gamete gets one 

 of each pair; that is, a chromosome for color and a chromosome for size. 

 Pick out many gametes without looking. How many chromosomes must 

 there be in each? Keep a record of the kinds of gametes produced. 



15. {Optioiial) To test your understanding of reduction division when 

 you are working with two pairs of chromosomes show what possible 

 gametes may be formed from a primary sex cell with these pairs of char- 

 acters: black and white, and rougrh and smooth. 



16. {Optional) Work out the kinds of gametes produced by a tri- 

 hybrid, Ts Yg Pw when T stands for tallness, s for shortness, Y for yel- 

 low seed, g for green seed, P for purple blossom and w for white blossom. 



17. {Optioiml) In one kind of sweet pea there are purple flowers (P), 

 and the gene is linked with a gene for long pollen grains (L). Another 

 kind of sweet pea has red flowers (r) and a linked gene for spherical pol- 

 len grains {s). The parents, therefore, are PL PL and rs rs. Illustrate by 

 diagram what ofl^spring may be expected in the F^ and the F„ generations. 



18. (Optional) The two chromosomes of a pair may be so twisted in 

 reduction division that when they separate the two have exchanged 

 pieces. This is called crossing over. A trihybrid might have genes abc in 

 a row in one chromosome and a'b'c' in another. After twisting, one chro- 

 mosome may have abc', the other a'b'c. What effect has crossing over on 

 the usual ratios? 



19. If a mother has a recessive gene for color blindness and has four 

 children, two of whom are sons, must one son be colorblind? Work out 

 a diagram and explain your answer. How could a colorblind woman be 

 produced? 



Further Activities in Biology 



1. There are many interesting breeding experiments that you can carr)^ 

 out. Mice breed quickly and the inheritance of coat color can be studied. 

 Do not attempt experiments before you know how to care for the mice. 

 Cross gray and white mice. If you can obtain them, cross yellow and 

 black mice. Consult your teacher, for some crosses involve complications 

 which you will not be able to explain until you know much more about 

 genetics. 



2. Fruit flies can be obtained at any supply house and can be bred 

 easily. A Turtox leaflet gives you full instructions for culturing them. 



3. The Brooklyn Botanic Garden, Brooklyn, New York, will sell you 

 sorghum and pea plants which show a three to one ratio. You will be in- 

 terested to discover the characters for yourself. 



