Genetics Practice Problems, book #1
1. In peas, the gene for tallness is dominant to the gene for shortness. What offspring phenotypes and genotypes would be expected from the following crosses, and in what proportions?
a. Heterozygous x heterozygous
b. Heterozygous x homozygous tall
c. Homozygous tall x homozygous short
2. If blue eye color in man is recessive to all other colors, could:
i. Brown eyed parents have a blue eyed child?
ii. Blue eyed parents have a brown eyed child?
3. The gene for yellow seed coat in peas is dominant to its allele, green. What offspring phenotypic and genotypic ratio would be expected from a cross between a pea plant known to be heterozygous for coat color and one which produced green seeds?
4. From a mating between two normal winged drosophila, 27 dumpy winged and 79 normal winged offspring were produced.
i. What is the nature of the dumpy winged gene? ii. What were the parental genotypes?
5. In a cross between a dumpy winged fly and one of the parents in the previous question, how many normal winged flies would be expected among 120 offspring?
6. Albinism, the inability to synthesize chlorophyll, is a recessive character in a number of green plant species. If a tobacco plant known to be heterozygous for albinism is self-pollinated and 600 of its seeds are subsequently germinated, how many seedlings would be expected to be albino? And how many would be expected to have the parental genotype?
7. A man and his wife can both taste phenylthiourea. They have four children, two of whom are unable to taste. What are the parental genotypes?
8. Construct a pedigree diagram for the following families:
a. A man and his wife are both tasters and they have two taster sons, a taster daughter and a non-taster daughter. One of the sons is married to a non-taster and they have a non-taster daughter.
b. A taster man has a taster son, a non-taster son, and a taster daughter by his first marriage and two non-taster daughters by his second marriage. His first wife was never tested but his second wife was a non-taster. The daughter of his first marriage subsequently married a non taster and produced eight children, all of whom were tasters.
9. A pigeon fancier had a true breeding strain of bird whose outer wing pinion length was 20 cm in the adult stage. When this strain was crossed with a strain having 16 cm pinions, the offspring were uniformly of 18 cm length. Since this was suitable for show purposes he carried out in-bred matings between the 18 cm birds. The offspring of these matings, however, while producing mostly birds whose wing pinion length was 18 cm, also produced birds of other wing types, 16 and 20. Show diagrammatically, the two generations of pigeons, showing the genotypes to account for these observations.
10. Antirrhinums have pink, white or red flowers. A number of crosses were made and seeds were collected from each cross. The seeds were germinated and the kinds of flowers subsequently produced were recorded as follows:
red x pink gave 126 red and 131 pink white x pink gave 88 white and 92 pink
red x white gave 115 pink
pink x pink gave 43 white, 39 red and 63 pink What genetic mechanism can account for these results?
11. A farmer crosses his roan bull with three groups of cows. Cows of group A were white, cows of group B were red and cows of group C were roan. What proportions of the different coat colors would he expect in the offspring of each group of cows?
12. If the same farmer decided to make his shorthorn herd exclusively roan coat by selling all white and red calves, would the color of the bull he used...
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