242 PRINCIPLES OF ANIMAL BIOLOGY 



the Fi animals are crossed with red normal-toed ones and produce 80 offspring, how 

 many of these should be red and normal-toed? 



29. Black is dominant over white in sheep, and in certain breeds horns are domi- 

 nant in males but recessive in females. A homozygous black hornless ewe of one of 

 these breeds is mated with a homozygous white horned ram. If their offspring is 

 female, what will be its appearance? If male, what appearance? If a number of 

 Fi males and females from such parents are mated together, and produce 32 offspring, 

 equally divided between the sexes, how many of these will be black horned females? 

 How many white horned males? 



30. Red eye (B) is dominant over brown (6) in Drosophila, and pigmented ocelli 

 (WO) dominant over white ocelli (wo). A certain brown-eyed fly with pigmented 

 ocelli is mated with one having red eyes and white ocelli, and some of their offspring 

 have brown eyes and white ocelli. What are the formulas of the parents? 



31. In Drosophila, gray body is dominant over ebony, and straight wing dominant 

 over curved. A certain gray-bodied curved-winged female is mated to a gray straight- 

 winged male, and they produce some ebony curved offspring. Out of a total of 

 40 offspring, how many should be ebony straight? How many gray curved? 



32. Each cell of the muscles of a certain male bug contains 27 chromosomes. How 

 many chromosomes in its spermatogonia? How many in its mature spermatozoa? 

 How many chromosomes in the body cells of the female of the same species? How 

 many in her mature eggs? How many in fertilized eggs? 



33. Can a male Drosophila be homozygous for a sex-Unked character? From 

 which parent does a male Drosophila receive his sex-linked genes? To which sex 

 among his offspring does he transmit his sex-linked characters? If a gene were 

 located in his Y chromosome, to what offspring would he transmit it? 



34. Color blindness is a sex-linked recessive, and sex in man is determined essen- 

 tially as in Drosophila. A girl of normal vision whose father was color-blind marries 

 a color-blind man. What is the chance that their first child will be color-blind? 



35. A woman of normal vision, whose father was color-blind, marries a man of 

 normal vision whose maternal grandfather was color-blind. Among their three 

 daughters how many should be color-blind? 



36. A. color-blind boy's parents and grandparents all had normal vision. What 

 was the formula of his maternal grandfather? Of his mother? Of his maternal 

 grandmother? 



37. Yellow body (y) in Drosophila is a sex-linked character recessive to gray 

 body ( F). A certain gray female mated with an unknown male produced some yellow 

 and some gray offspring of both sexes. What was the formula of the original female? 

 What was the appearance of the male to which she was mated? 



38. A female fruit fly with sable body (s) is mated with a male having gray body 

 (S). Their daughters are gray, their sons sable. In what cliromosomes are the 

 genes S and s? 



39. A barred rock hen mated with a black cock produced black daughters and 

 barred sons. Using B and b to represent the genes, give the formulas of the two 

 parents. 



40. The genes for purple eye (normally red) and curved wings (normally flat) in 

 Drosophila are in the same pair of chromosomes, and the normal red eye and flat 

 wings are dominant. A homozygous purple-eyed flat-winged fly is crossed with a 

 homozygous red-eyed curved-winged fly. One of their daughters is mated with a 

 purple curved male. What kinds of offspring will they produce, and in what pro- 

 portions, assuming that 21 per cent of the pairs of chromosomes break between the 

 genes for eye color and wing shape? 



