Download Plant Science 446/546

Plant Science 446/546
Class Test March 25, 1996
Ag.Sci. Room 339
9.00pm to 10.30pm
Name :
Answer all 7 questions
A total of 100 points are available
Points available from each part of each question
are shown in bold square parenthesis
Try to be as brief and concise as possible
Please write in a legible form
Show any working/calculations
Make sure that any additional paper used
is attached to the questionnaire
1.
A cross is made between two homozygous barley parents. One parent is tall and
resistant to mildew (i.e., TTRR) and the other parent is short and susceptible to
mildew (i.e., ttrr). Height and mildew resistance are both qualitatively inherited
with tall is dominant to short and resistant dominant to susceptible.
1a.
If the F1 family from this cross were self pollinated how many F2 plants
would you need to grow to ensure a 99% certainty of having at least one
plant which was resistant to mildew and short [4 points].
1b.
2a.
Consider now the same cross (TTRR x ttrr) and in a breeding program 6400
F2 plants were evaluated. At harvest only the short mildew resistant plants
were selected and grown as F3 head rows (i.e. only these selected types were
evaluated at the F3 stage). Determine the expected number of genotypes
and phenotypes you would have when you harvest the F3 rows [6 points].
Given values for the variance of the F2, and variance of both parents (P1 and P(2)
and the F1, estimate h2b and explain what this value means in genetic terms [5
points].
V(F2)
V(F1)
V(P1)
V(P2)
2b.
436.72
111.72
164.13
109.33
Given the variance from two parents (P1 and P2), the F1, F2, B1 and B2 families,
estimate the narrow-sense heritability (h2n) and explain what the value means in
genetic terms [10 points].
V(P1)
V(P2)
V(F1)
V(F2)
V(B1)
V(B2)
3a.
=
=
=
=
=
=
=
=
=
=
9.5
7.4
8.6
17.7
14.3
15.2
Past researchers have shown that the inheritance of plant height in Brassica napus
can be explained by an additive/dominance model. Below are shown family means,
the standard errors (s.e.), (NOTE these are not the standard errors of the mean), and
the number of plants that these data are estimated from the P1, P2, F1 and F2
families.
Family
Mean
s.e.
Plants
P1
P2
F1
F2
40.2
19.3
35.4
22.7
0.142
0.151
0.099
0.462
31
31
31
31
Using an appropriate statistical test determine if the result from past researchers is
true based on these data (i.e. that the additive/dominance model is adequate to
describe the observed variation) [12 points].
3b.
If the additive/dominance model does not explain the variation found for plant
height, list three reasons what might be the cause? [3 points].
1.
2.
3.
4a.
Explain the meaning of a "Test cross" as applied to testing linkage disequilibrium in
qualitative genetics. [1 point].
4b.
Two homozygous barley genotypes are chosen for a linkage study. One of the
parents had a long awn and short in stature. The other parent has a short awn and is
tall in stature. Long awn is controlled by a single dominant gene (AA = Long awn =
dominant over aa) and plant height is controlled by a single dominant gene (TT =
Tall = completely dominant over tt). The two lines are crossed (i.e ttAA x TTaa) and
the resulting F1 is test crossed to a homozygous genotype with short awn and short
stature (aatt). 3000 plants from the test cross are grown and the following
phenotypic frequencies were observed:
Tall and Long awn (TA)
Short and Long awn (tA)
Tall and Short awn (Ta)
Short and Short awn (ta)
308
1076
1324
292
Determine the percentage recombination [2 point].
4c.
A sample of seed from the original F1 (i.e., TtAa) was increased to the F2 and the
following are the numbers of plant types observed:
Tall and Long awn (TA)
2650
Short and Long awn (tA)
1133
Tall and Short (Ta)
1163
Short and Short awn (ta)
54
Based on the recombination percentage from question 4b (above), determine the
expected number of each phenotype in the F2. Use a Chi-square test to determine if
your expected numbers are the same are those observed in the F2, write answer on
next page [12 points].
5.
Consider that the additive/dominance model of inheritance is adequate to explain
the variation in the cross between P1 and P2, two diploid homozygous parents.
5a.
In terms of m, [a] and [d], what would be the expected performance of each
parent (P1 and P2), the F1 and F2 families and both backcross families (B1
and B2) [6 point].
P1 =
P2 =
F1 =
F2 =
B1 =
B2 =
5b.
In a single cross between two homozygous barley cultivars (P1 and P2) the
yield of P1 was 3694 lbs/acre, the yield of P2 was found to be 2744 lbs/acre
and the one of the backcross families (B1) showed a yield of 3622 lbs/acre.
Given that the additive/dominance model is adequate to explain genetic
variation for yield in barley, what would the expected yield of the F1, F2 and
B2 families be? [4 points].
6a.
Explain (using A as a dominant allele and a as a recessive allele) the difference
between genotypes that are nulliplex, simplex, duplex, triplex and quadriplex for a
single dominant gene [2 points].
6b.
Assuming no complications such as double reduction, what would be the expected
ratio of nulliplex, simplex, duplex, triplex and quadriplex resulting from a cross
between two autotetraploid lines that are duplex for a single gene (i.e. AAaa x
AAaa) [8 points].
7.
A new oil crop (Brassica gasolinous) has been discovered which may have potential
as a renewable biological fuel oil substitute. This diploid species is tolerant to
inbreeding and is self compatible. A preliminary genetic experiment was designed
to examine the inheritance of seed yield (YIELD) and percentage oil content
(%OIL). This experiment involved a 4 x 4 half diallel (including selfs). The four
homozygous parental lines are represented by the codes AAA, BBB, CCC and
DDD.
The half diallel array values (averaged over two replicates), array means, general
combing ability (GCA) values, mean squares from the analyses of variance (Griffin
style), Vi and Wi values (Hayman & Jinks analysis), variance of array means (Vxr)
and parental variances (Vp), and the one-way analyses of variance for Vi+Wi and ViWi are shown below for each character.
Array Means
YIELD
OIL
AAA
BBB
CCC
DDD
40.5
38.5
37.0
32.5
10.0
20.5
20.5
23.0
24.5
25.0
26.0
27.5
30.5
31.0
36.0
CCC
DDD
AAA BBB
CCC
DDD
29.5
28.0
20.5
19.5
18.5
AAA BBB
Array means 37.1
29.1
25.8
20.4
22.1
24.7
27.6
29.8
GCA values
+1.0
-2.3
-7.7
-3.9
-1.3
+1.6
+3.7
+9.0
Analyses of Variance
Source
df
YIELD
%OIL
G.C.A.
S.C.A.
Replicate Blocks
Replicate error
3
6
1
9
796.5
90.5
0.4
51.48
180.6
30.1
0.1
5.72
Vi and Wi values
Vi
AAA
BBB
CCC
DDD
YIELD
Wi
46.2
218.2
297.7
344.3
171.3
376.7
436.7
472.3
%OIL
Vi
Wi
15.6
36.3
58.3
97.3
50.7
75.0
98.0
132.3
Vxr and Vp values
Vxr
YIELD
%OIL
196.9
44.4
Vp
687.6
180.7
One-way analyses of Variance
Source
df
Vi+Wi
Between
Within
3
4
8760
133
7a.
YIELD
Vi-Wi
28.0
17.0
%OIL
Vi+Wi
Vi-Wi
628
115
7.68
4.77
Without using regression, estimate the narrow-sense heritability (h2n) for
seed yield, and explain this values in genetic variance terms [5 points].
7b.
Explain the analyses for YIELD and outline any conclusions which can be drawn for
these data [8 points].
7c.
Explain the analysis for %OIL and outline any conclusions which can be drawn
from these data [8 points].
7d.
Which one of these four genotypes would you choose as a parent in your breeding
program and explain your choice [4 points].
BONUS QUESTION
Describe any difficulties suggested from these analyses in a breeding program
designed at selecting lines with high yield and high percentage of oil [5 bonus
points].