Unit 2 Math Practice ANSWERS
Name________________________________
1) The recombination frequency between gene A and gene B is 14.5% and the recombination frequency
between gene A and gene C is 8.6%. If the order of these genes on a chromosome is B-A-C, then the
approximate recombination frequency between gene B and gene C should be 23.1%.
2) Find the recombination frequency between two genes on the same chromosome in peas given the
following crosses:
P (true-breeders): rough – soft pea x smooth – hard pea
F1: all offspring are rough – soft
Test cross: rough – soft pea (from F1) x smooth – hard pea
F2:
127 rough – soft
113 smooth – hard
17 rough – hard
9 smooth - soft
Recombination frequency = 9.8%
3) In Drosophila, there is a dominant gene for gray body color and another dominant gene for
normal wings. The recessive alleles of those two genes result in black body color and vestigial wings,
respectively. Flies homozygous for gray body and normal wings were crossed with flies that had
black bodies and vestigial wings. The F1 progeny were then test-crossed with the following results:
Phenotype
Gray body, normal wings
Black body, vestigial wings
Gray body, vestigial wings
Black body, normal wings
# Progeny
236
253
240
242
What is the recombination frequency for these two genes? 49.6%
Would you say that these two genes are genetically linked? no Why/why not? 50% is “max” RF and is
associated with normally-unlinked genes. RF %s of significantly less than 50% are necessary to ID genes
as “linked”
If they are linked, how many map units apart are they on the chromosome? 49.6 map units
4) Calculate the probability (in fraction form) that two parents with the following genotype
combination:
AaBBccDd x AabbCcDd
will produce an offspring with the genotype combinations:
a) aaBbCcDd 1/16
b) AABbccdd 1/32
c) AabbCcDD 0
5) In a certain species of flowering plant, the purple allele ‘A’ is dominant to the yellow allele ‘a’. A
student performed a cross between a purple-flowered plant and a yellow-flowered plant. When
planted, the 146 seeds that were produced from the cross matured into 87 plants with purple flowers
and 59 plants with yellow flowers.
Calculate the chi-squared value for the hypothesis that the purple-flowered parent was heterozygous for
the flower-color gene. Give your answer to the nearest tenth. 5.4
Based on your result, the null hypothesis is rejected. (accepted/rejected)
6) A large ear of corn has including 271 Purple & Smooth kernels, 73 Purple & Shrunken kernels, 63
Yellow & Smooth kernels, and 26 Yellow & Shrunken kernels. This ear of corn was hypothesized to
have been produced by a dihybrid cross (PpSs x PpSs.)
Calculate the chi-squared value for the hypothesis that this particular ear of corn was the progeny
of the dihybrid cross PpSs x PpSs. Give your answer to the nearest tenth. 8.0
Based on your result, the null hypothesis is rejected. (accepted/rejected)
7) A heterozygous red eyed female was crossed with a red eyed male. The results are shown below. Red
eyes are sex-linked dominant to white. Determine the chi square value for this scenario. Round to the
nearest hundredth. 6.83
Phenotype
Red eyes
White eyes
p
0.05
0.01
1
3.84
6.64
2
5.99
9.32
# flies observed
134
66
3
7.82
11.34
Degrees of Freedom
4
5
9.49
11.07
13.28
15.09
6
12.59
16.81
7
14.07
18.48
8
15.51
20.09