Genetics study questions & sample questions

1. A. Construct a set of data from an imaginary monohybrid(heterozygote) testcross in which at least 100 progeny were counted. These data should be consistent with chance expectations (50:50) according to Chi-square analysis. Then generate data which show the same PROPORTIONS of offspring as the first set, but which is NOT consistent with chance expectations.

B. Do the same thing but this time, construct data for a monohybrid cross.

C. Is it possible to construct a data set that will satisfy the above requirements, but the larger group will be the one consistent with chance and not the smaller? If so, demonstrate an example; if not, explain why not.

D. Draw a conclusion about sample size and interpretation of data. Is this always true? If not, give an example of when it might not be and explain. If so, explain why.

2. What is the probability of:

a. tossing a fair coin and getting 5 heads in a row?

b. tossing a fair coin and getting two heads & a tails [in any order]?

c. tossing two identical fair coins and getting heads on both the first time & tails on both the second?

d. tossing two identical fair coins and getting heads on one & tails on the other both times?

e. tossing two non- identical fair coins and getting heads on the dime, tails on the penny the first time & tails on the dime, heads on the penny the second time?

3. Map the following three genes. Be sure to write the phenotypes and genotypes of the parents, as well as the map distances. Calculate I.

The results of a testcross were:

Abc 18

Ab+ 207

A+c 24

A++ 2

+bc 1

+b+ 20

++c 208

+++ 20

4. An individual known to be triply heterozygous was testcrossed to produce progeny with the following phenotypes. What were the phenotypes of the two parents? Map the genes. Your final answer should include the genotypes of both parents with the genes arranged in the correct order and in the correct allelic configuration (i.e. dominant and recessive alleles arranged properly on each chromosome). Map distances and interference must also be calculated. Place the completed maps in the upper left of the answer blank. DO NOT USE ANY OTHER PAPER. DO NOT ATTACH OTHER PAPER.

+ + + 10

+ + D 436

+ b + 1

a + + 55

a + D 5

a b + 410

+ b D 79

a b D 4

------------------- or

+ + + 12

+ + D 1

+ b + 35

a + + 456

a + D 40

a b + 4

+ b D 449

a b D 3

------------------- etc.

5. Most razamatazes have shiny silver hair, purple noses and orange eyes, but there are recessive mutations which result in dull gray hair (d), red noses (r) and green eyes (g). A cross between wild-type males and females known to be heterozygous at all three loci produced the following progeny: 985 wild type females; 1000 males with various phenotypes: 26 wild type; 420 red noses; 3 dull hair; 32 green eyes; 45 dull hair & red noses; 452 dull hair & green eyes; 1 red noses & green eyes; 17 dull hair, red noses & green eyes.

6. A female hypothetical organism with brown eyes (b) and wild type orange nose (+) is crossed with a wild type (pink) eye (+), green nose (G) male. All daughters have wild type pink eyes and green noses; all sons have brown eyes and orange noses. When the F₁ are crossed among themselves, the following are obtained:

sons daughters

+ + 37 35

+ G 201 223

b + 219 197

b G 43 45

- or -

sons daughters

+ + 132 125

+ G 143 141

b + 162 134

b G 130 133

7. The offspring of a testcross had the following phenotypes. Describe as fully as possible the genetic map, including the most likely parents' genotypes and phenotypes, autosomal or sex-linked, map distances, interference, etc.

+ + + 67

+ + m 113

+ l + 5

k + + 621

+ l m 618

k l + 119

k l m 57

------------------- or

+ + + 13

+ + M 2

+ l + 858

k + + 125

+ l M 128

k l M 15

k + M 859

------------------- or

a b d 81

a b + 3

a + d 372

a + + 72

+ + + 487 65

+ b + 476 322

+ b d 84

+ + d 1

8. Vermillion eyes (v), lozenge-shaped eyes (lz), and cut wings (ct) are recessive traits in Drosophila. A cross between females heterozygous at these three loci and wild type males produced the following progeny. Analyze this map: the linkage arrangement of these genes - order, map distance, interference, and the genotypes of original mating pair.

males females

+ + + 45 1010

+ + lz 34

+ ct + 441

+ ct lz 1

v + + 0

v ct lz 42

v ct + 37

v + lz 430

9. 4. The results of a preliminary experimental test cross looked interesting, so the experiment was repeated but more offspring were counted the second time. Are the genes linked? If so, estimate the distance between them? What were the parents' genotypes and phenotypes? Explain your logic.

green purple

hair nose EXPERIMENT 1 EXPERIMENT 2

blue orange 28 2800

blue purple 22 2200

green orange 23 2300

green purple 27 2700

10. It is now possible to test people for heterozygosity of the cystic fibrosis (cf) gene. Two known heterozygotes are married, and plan to have six children. What is the probability that they will have:

a. four girls?

b. exactly one child with cf?

c. that the third and fifth children have cf, but the others are normal?

d. three with cf?

e. five with cf?

f. only one boy?

g. only one boy, and three children with cf?

h. only one boy, and three children with cf?

i. only one boy, and he is the only child with cf?