Zoo/Bot 3333

Genetics

Quiz 2

10/2/09

For answers to the quiz, click here

The accompanying pedigree shows a very unusual inheritance pattern that actually did exist. All progeny are shown, but the fathers in each mating have been omitted to draw attention to the pattern.

1. Which of the following is the most likely explanation of this data?

a) A Y-linked lethal; b) An autosomal dominant with sex-limited inheritance; c) an X-linked recessive; d) an X-linked dominant; e) none of the above is likely.

The data set below was taken from a real human population, where many families were tested for the ability to taste the chemical phenylthilcarbamide (PTC). These matings were grouped into three classes and the progeny were totaled with the following results:

Children
Parents / Number of families / Tasters / Non-Tasters
1) Taster x taster / 425 / 929 / 130
2) Taster x nontaster / 289 / 483 / 278
3) Nontaster x nontaster / 86 / 5 / 218

2. Assuming the taster phenotype is dominant and the nontaster is recessive, which of the following is true?

a) The first data set should show a 3:1 ratio of taster:nontaster; b) the second data set should a 1:1 ratio of taster:nontaster; c) the taster children in data set three are probably the result of mutation to the dominant phenotype; d) all of the above; e) none of the above.

3. Which experiment was a direct demonstration that crossing over results in the physical breaking and rejoining of chromosomes?

a) The work of Nettie Stevens; b) the work of Morgan and Sturtevant; b) the work of Creighton and McClintock; d) the work of Curt Stern; e) two of the above are correct.

Parents / F1 phenotypes / F2 phenotypes
orange x blue / All orange / 203 orange, 67 blue
purple x blue / All purple / 152 purple, 52 blue
purple x orange / All sienna / 86 sienna, 41 orange, 43 purple
orange x tan / All orange / 130 orange, 60 tan, 44 blue
tan x blue / All purple / 181 purple, 79 tan, 60 blue

Questions 4-5 pertain to the following: On the planet Riza, the “luminescent horgon” is a flower that has many color variations. Crosses between several varieties of the plant yield (chart at right):

4. The color variations observed here indicate that:

a) the sienna allele is dominant to the purple allele ; b) two gene loci are involved; c) this cross is an example of complementary gene action; d) all of the above; e) none of the above.

5. If the blue F2 offspring from cross 4 are crossed to a true-breeding orange strain, what will be the ratio of progeny?

a) all orange; b) 1 orange: 1 blue; c) 3 orange: 1 blue; d) all sienna; e) none of the above.

Phenotype / Number of progeny
+ b c / 436
a + c / 91
a b c / 6
+ + c / 92
a + + / 440
a b + / 87
+ + + / 8
+ b + / 98

Questions 6-7 pertain to the following cross. A fly heterozygous for three different genes (AaBbCc) is testcrossed to a fly homozygous recessive for these three mutations. The following progeny types are produced (chart at right):

6. The distance between the a and b genes is:

a) 8.05 map units; b) 14.2 map units; c) 15 map units; d) 15.3 map units; e) 16.1 map units.

7. True or false. Only about 1.1% of the expected double crossovers are observed in this cross.

Phenotype / Number of progeny
+ b c / 228
a + c / 19
a b c / 20
+ + c / 234
a + + / 231
a b + / 227
+ + + / 21
+ b + / 20

Questions 8-9 pertain to the following cross. A fly heterozygous for three different genes (AaBbCc) is testcrossed to a fly homozygous recessive for these three mutations. The following progeny types are produced (chart at right):

8. True or false. The a and c genes are in the trans phasing configuration in the heterozygous parent.

9. The above data set indicates that the c gene is:

a) unlinked to the a gene; b) linked to the b gene; c) 3.9 map units from the b gene; d) all of the above; e) none of the above.

10. The following asci were obtained in Neurosopora when a wild type strain (td+) was crossed to a mutant strain unable to grow in the absence of tryptophan (td-).

Spore pair / Ascus type
1-2 / td+ / td- / td- / td- / td+
3-4 / td+ / td+ / td- / td+ / td-
5-6 / td- / td+ / td+ / td- / td-
7-8 / td- / td- / td+ / td+ / td+
total / 53 / 7 / 47 / 8 / 5

The distance between the td locus and the centromere is:

a) 5.4 map units; b) 8.3 map units; c) 10.8 map units; d) 16.6 map units; e) none of the above.