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2. Soybeans are rich in protein. Raw soybeans, however, may contain a trypsin inhibitor. This is a
chemical which prevents the digestion of protein. The presence of this trypsin inhibitor is
A B C
genetically controlled. A single gene has alleles T , T and T each of which codes for a
different sort of trypsin inhibitor. These alleles are codominant so plant with the genotype
A B
T T will produce two sorts of trypsin inhibitor, inhibitor A and inhibitor B. A fourth,
o
recessive allele, T does not code for a trypsin inhibitor. This information is summarised in the
table.
Allele Inhibitor produced
A A
T
B B
T
C C
T
o None
T
(a) The inheritance of trypsin inhibitors in soybeans is an example of multiple allele
inheritance. Explain how multiple allele inheritance differs from polygenic inheritance.
(c) Two soybean plants were crossed and the seeds collected and counted. The results are
shown in the table.
Inhibitors present in seed Number of seeds
A and B 23
A 25
B 48
(i) Complete the genetic diagram to explain the results of this cross.
Phenotypes of parents:.................................. .......................................
Genotypes of parents:.................................. .......................................
Genotypes of gametes ......................................................................................
Genotypes of offspring: ....................................................................................
Phenotypes of offspring Inhibitor A Inhibitor A Inhibitor B
and
Inhibitor B
(3)
(ii) A chi-squared test was applied to the data collected in this investigation. Explain
why statistical tests such as the Chi-squared test should be carried out on data like
these.
, An investigation was carried out on the insects living on bean crops. The graph shows the
relationship between the biomass of primary consumers, secondary consumers and producers.
100
90 P rim a ry
co n su m e rs
80
70
C onsum er 60
–2
b io m a s s /g m
50
40
30
20
10 S e c o n d a ry
c o n su m e rs
0
0 200 400 600 800 1000
–2
P ro d u c e r s b io m a s s /g m
(d) Briefly describe how the data on the biomass of the producers might have been collected.
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