21. The most common phenotype in a natural population is referred to as the
(a) genotype (b) wild type
(c) autosome (d) mutant phenotype
22. Human males are much more likely to be have hemophilia (a failure of blood to clot properly) than human females. This is the case because
(a) hemophilia is a contagious disease to which males are more susceptible
(b) the gene for hemophilia is carried on the Y chromosome
(c) hemophilia is carried on the autosomes
(d) the gene for hemophilia is sex-linked
23. In a particular species of mammal black hair (B) is dominant to green hair (b) and red eyes (R) are dominant to white eyes (r). If a BbRr individual is mated with a bbrr individual the expected phenotypic ratio of the offspring is 1 black-red : 1 black-white: 1 green-red : 1 green-white. However, when you mate these individuals you find that the phenotypic ratio of the offspring is 6 black-red : 1 black-white : 1 green-red : 6 green-white. What could account for this difference?
(a) The genes for hair color and the genes for eye color are carried on different chromosomes
(b) The expected results did not take genetic recombination into account
(c) The genes for hair color and eye color are linked
(d) The genes for hair color and eye color show dependent assortment
24. In the problem no. 23 the observed F2 generation distribution of offspring was: blackred 1,070; black-white 177; green-red 180; green-white1072. Based on this data, what is the recombination frequency ?
(a) 30 percent (b) 7 percent
(c) 17 percent (d) 14 percent
25. How many map units is a recombination frequency of 5 percent equal to?
(a) 2.5 centimorgans (b) 10 centimorgans
(c) 5 centisturtevants (d) 5 centimorgans
26. A linkage map
(a) orders genes on a chromosome based on recombination frequencies
(b) can only be constructed for sex chromosomes
(c) orders genes on a chromosome based on their location with respect to a stained band
(d) shows the actual ordering and spacing of genes on a chromosome
27. A male bee is
(a) X Y (b) diploid
(c) hapliod (d) Z W
28. What is the probability that a male will inherit an X-linked recessive gene from his father?
(a) 0 (b) 25 percent
(c) 50 percent (d) 75 percent
29. Duchenne muscular dystrophy is caused by a sex-linked recessive allele. Its victims are almost invariably boys, who usually die before the age of 20. Why is this disorder almost never seen in girls?
(a) Sex-linked traits are never seen in girls
(b) The allele is carried on the Y chromosome
(c) Nondisjunction occurs in males but not in females
(d) In order to express an X-linked recessive, a female must have two copies of the gene
30. Which of the following human genetic disorders is sex linked?
(a) hemophilia (b) PKU
(c) cystic fibrosis (d) achondroplasia
