Download Problem Set 3

BIO 207S (2005)
GENETICS
Problem Set 3
Due Friday, Febuary 25, by 4:55 p.m.
Place in box labelled BIO 207 Problem Sets
1. A true breeding mouse strain exhibits two different rare traits. When a male from
the true breeding strain is crossed to a wild-type female, all of the female F1
progeny exhibit both traits whereas all of the male F1 progeny look wild type.
a) What is the model of inheritance of the two traits?
b) The male and female F1 mice described above are crossed to one another
to produceF2 progeny. Of the male F2 progeny, 40%have both traits (the
rest of the F2 males either appear wild type or have only one trait or the
other). What fraction of the female F2 progeny would you expect to have
both traits?
c) What is the map distance between the genes for the two traits?
2. Homozygous recessive h h flies were crossed to homozygous recessive rd rd flies
(both strains were homozygous normal for all other genes). The resulting F1 flies
were crossed to h h rd rd flies, and 1000 F2 progeny were collected. What F2
progeny phenotypes and numbers do you expect in the F2 progeny?
3. The raisin eye (rai+) gene is located 9 map units away from the hairy body gene. The
normal (rai+) allele is dominant. Homozygous recessive h h flies were crossed to
homozygous recessive rai rai flies (both strains were homozygous normal for all other
genes). The resulting F1 flies were crossed to homozygous h h rai rai flies, and 1000 F2
progeny were collected.What F2 progeny phenotypes and numbers do you expect in the
F2 progeny?
4. A true-breeding hot pepper plant of genotype GGDD that produces yellow, round
peppers is crossed to a true-breeding hot pepper plant of genotype ggdd that produces
green, wrinkled peppers. The F1 progeny are of genotype GgDd and all bear yellow,
round peppers. F1 plants were then test crossed to ggdd plants and the following progeny
plants were produced:
Phenotype
Number
green, wrinkled
114
yellow, round
112
yellow,
88
wrinkled
green, round
86
total
400
(G/g = yellow/green, D/d = round/wrinkled)
(a) How many progeny are expected for each phenotype class, assuming independent
assortment? (b) Use the chi-squared test (Chi-squared able is in your text book) to decide
if there is evidence of independent assortment versus linkage between the two genes.
Give the Chi square value, the approximate P value (just give the range of P values from
the chi-squared table, as we did in class), and the appropriate degrees of freedom (df).
State whether your findings are consistent or inconsistent with the hypothesis of
independent assortment. (c) If you wanted to be more stringent** about whether to reject
or accept your hypothesis of independent assortment based on the P value obtained,
would you raise or lower the cut-off P value?
**i.e., you are less willing to be tolerant of deviation from the expected values
(d) When we are assessing the data for independent assortment vs linkage, why do we
assume independent assortment and then test whether the data fit independent assortment,
as done above? Why do we not assume linkage and then test whether the data fit the
linkage model?
5, In maize, A, B, and D are three linked genes, with a, b, and d being recessive alleles
of these three genes, respectively. A homozygous normal strain was crossed to a triple
homozygous recessive strain. The resulting F1 progeny were crossed to the triple
recessive again; the resulting progeny phenotypes were:
A b d
a B d
a b d
A B d
a b D
A B D
A b D
a B D
Total:
21
120
298
66
72
301
131
13
1022
Show the correct order of the genes A, B, and D. Construct a map showing the distances
between the genes, and calculate the coefficient of coincidence.