Bbrr x bbrr

BIOLOGY 160 GENETICS PROBLEMS

5. Andalusian chickens may be either black, white, or gray. The gene for black is not dominant over the gene for white, nor is the gene for white dominant over the gene for black. When a black rooster is mated to a white hen, all gray chicks are produced. When gray chickens are mated, the chicks are black, gray, and white.

Using a Punnett Square, demonstrate how feather color is inherited in Andalusian chickens.

Is the inheritance of feather color in this problem an example of incomplete dominance?

Why would it be impossible to establish a true breeding flock of gray Andalusian chickens?

6. In guinea pigs, black coat color (B) is dominant to white (b), and a rough coat (R) is dominant to smooth (r). What are the expected genotypic and phenotypic results of the following crosses?

BBRR x bbrr

BBrr x bbRR

Bbrr x bbRr

BBRr x BbRr

BbRr x BbRr

7. A pure-breeding black, smooth guinea pig was mated to a pure-breeding white, rough female. They produced several litters, and eventually, five males and twenty females resulted from this mating. These females were bred to the males. By the time their litters were produced, there were 96 offspring. Theoretically how many phenotypic classes should have appeared, and in what relative numbers?

8. In rabbits, black fur is dominant to brown, and long hair is dominant to short hair. A male is mated to several brown, short-haired females. These matings result in the following offspring: 11 brown, long-haired: 16 black, long-haired; 12 brown, short-haired; 15 black, short haired. Express the genotype and phenotype of the male.

9. In cattle, the polled condition (H) is dominant to the horned condition (h). A cross between an individual with red coat (R) and white coat (W) results in roan (RW). A polled, red bull is mated to three cows. With cow A, which is horned and white, a polled roan calf is produced. With cow B, which is horned and roan, a horned, red calf is produced. With cow C, which is polled and red, a

horned calf is produced. What are the genotypes of all individuals; the bull, cows A, B, and C, and calves A, B, and C?

10. A roan bull which is heterozygous for the polled condition is mated to several cows of identical genotype to his. How many roan, polled animals should be produced out of 16?

11. In man, the determination of sex depends upon whether the male sperm carries an “X” chromosome (resulting in a female) or a “Y” chromosome (resulting in a male). In other words, body cells of females carry two X chromosomes, and those of the males carry one X and one Y. During meiotic division, the egg of the female must of necessity carry one X, whereas segregation of the X and Y in spermatogenesis results in some sperm that are Y bearing, and others that are X bearing. One human abnormality, called red-green color blindness, is the result of a recessive allele (Xb) carried on the X chromosome. The dominant allele (XB) produces normal vision. There is no copy of this gene on the Y chromosome. Consequently, the genotypes XBXB, XBXb, and XbXb are possible in females, but a male must be either XBY or XbY.

Working theoretically, answer the following questions:

a. Is it possible for a female to be color-blind?

b. Can two persons with normal vision produce a color-blind daughter?

c. Can two persons with normal vision produce a color-blind son?

d. Can two color-blind parents produce a child with normal vision?

Let us suppose that a woman with normal vision, whose father was color-blind, marries a color blind man.

e. What proportion of their sons may be expected to be color-blind?

f. What proportion of their daughters may be expected to be color-blind?

g. If one of their sons whose vision is normal marries a woman of the genotype , XBXB can they have any color-blind children?