Genetics 371B Autumn 1999, Problem set 1

Genetics 371B, Autumn 1999

Problem set 1 -- based on lectures 1-4

Due Wed Oct. 6 at the start of class

1. Wildtype Drosophila have red eyes, but there is a strain of flies with brown eyes. A brown-eyed homozygous male was mated to 20 genetically identical females with normal red eye color. Several F1 female flies (that all had the same eye color) were collected and mated to the original parental male. The resulting F2 progeny consisted of 313 brown-eyed and 330 red-eyed flies.

(a) Is the brown-eye phenotype dominant or recessive? Explain.

(b) Using upper and lower case symbols for the dominant and recessive alleles (clearly stating which is which ), give the genotypes of the flies in all three generations (parents, F1, and F2).

2. Flower color in the rare Great Northwestern Smelly Flower plant is controlled by a single gene. The plant comes in three varieties those that make white flowers with pink speckles , those that make white flowers with pink patches , and those that make pure white flowers. A botanist obtains one plant of each variety and does the following crosses with the three plants:

Cross F1 progeny

(i) white x white (selfed) 42 white

(ii) white x speckled 22 white, 26 speckled

(iii) patchy x patchy (selfed) 24 white, 51 patchy

(iv) speckled x speckled (selfed) 31 white, 59 speckled

(v) speckled x patchy 26 white, 29 speckled, 27 patchy

Using S, P, and W to indicate speckled, patchy, and white, respectively, formulate a hypothesis to explain the results. Your hypothesis must explain the observed F1 ratios, and must include the genotypes of the parents and the offspring in each case.

3. Dmitri's mother is blood type A, as is his wife; his father is blood type B, and younger sister is O. Dmitri's first son is also type O, while his second son is B. Draw a pedigree for this family, using the standard conventions (Roman numerals for generations, Arabic for individuals in order of birth, etc.), and indicate the genotypes of all members. What is Dmitri's blood type? Briefly explain your thinking. (Be sure to mark Dmitri in the pedigree.)

4. You discover a new bacteriophage that, upon infection of the host bacteria, quickly destroys the host DNA such that within minutes of infection, the only DNA that can be isolated from the infected cells in viral DNA. You find that the base composition of DNA from free virus (before infection) and of DNA isolated from infected cells is as follows:

Base Free virus Infected cells

A 20% 16%

C 28% 34%

G 40% 34%

T 12% 16%

What do these data tell you about the life cycle of the virus with respect to the structure of its DNA? Explain.

1.	Wildtype Drosophila have red eyes, but there is a strain of flies with brown eyes. A brown-eyed homozygous male was mated to 20 genetically identical females with normal red eye color. Several F1 female flies (that all had the same eye color) were collected and mated to the original parental male. The resulting F2 progeny consisted of 313 brown-eyed and 330 red-eyed flies.
	(a)	Is the brown-eye phenotype dominant or recessive? Explain.
	(b)	Using upper and lower case symbols for the dominant and recessive alleles (clearly stating which is which ), give the genotypes of the flies in all three generations (parents, F1, and F2).