GENETICS  PROBLEMS

1. In the human, normal pigmentation (A) is dominant to albinism (a). What output would be likely from the following matings, both genotypically and phenotypically?
AA x aa
Aa x aa
Aa x Aa
aa x aa

2. Man with normal pigment, whose father was an albino, marries an albino. What possibility is there that their first child would be an albino?

3. Man with normal pigment marries a woman with normal pigment. They have an albino child. What are the genotypes of all three individuals?

4. In chickens rose comb (R) is dominant over single comb (r). Rose-combed male is mated to a rose-combed female. Eighteen chicks are produced, ten of which are rose-combed, and eight of which are single-combed. What are the genotypes of parents?

5. Andalusian chickens might be either black, white, or gray. Gene for black is not dominant over the gene for white, nor is the gene for white dominant over the gene for black. When the 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, show how feather color is inherited in Andalusian chickens.
Is the inheritance of feather color in this problem an ex of incomplete dominance?
Why will 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 possible  genotypic and phenotypic results of the following crosses?
BBRR x bbrr
BBrr x bbRR
Bbrr x bbRr
BBRr x BbRr
BbRr x BbRr

7. 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 must have appeared, and in what relative numbers?

8. In rabbits, black fur is dominant to brown, and long hair is dominant to short hair. Male is mated to several brown, short-haired females. These matings causes 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 many cows of identical genotype to his. How many roan, polled animals must 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 should of necessity carry one X, while 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. Thus, the genotypes XBXB, XBXb, and XbXb are possible in females, but a male should be either XBY or XbY. Working theoretically, answer the following problems:

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 child with normal vision?

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

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

f. What proportion of their daughters might 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?

h. Could any of their daughters be “carriers” (heterozygous)?

i. Could the colour-blind trait be expressed in subsequent generations?

12. In Drosophilia, sex determination is similar as in the human. Normal flies have bright red eyes; a certain recessive sex-linked gene is responsible for white eyes. From a pure-breeding strain of red-eyed flies, a female is chosen and bred to a male from a pure-breeding strain of white-eyed flies.

a. Will all their offspring have eyes of the same color?

b. What would be the color of the eyes of male flies?

c. What would be the color of the eyes of female flies?

Now assume we let the male and female offspring of this original pair mate at random, and we collect exactly 100 of their offspring; 50 males and 50 females.

d. How many of the females must have white eyes?

e. How many of the males must have white eyes?

f. How many of the males must have red eyes?

g. How many of the females must have red eyes?