Populations of the moth Biston betularia live in Europe and in North America. The most common
phenotype on both continents is a pale wing colour with light‑grey shading (the typical form).
A moth phenotype with dark wing colour (the melanic form) also occurs on both continents.
Fig. 10.1 shows the typical form of the moth.
Fig. 10.2 shows the melanic form of the moth.
Fig. 10.1 Fig. 10.2
(a) Two melanic European moths were crossed together. The wing colours of the offspring were
Scallops, which are bivalve molluscs, are important commercially throughout the world.
The marine bay scallop, Agropecten irradians, has three distinct shell colours, yellow,
y
orange and black. The shell colour is controlled by a gene with three alleles, yellow, S ,
o b
orange, S , and black, S .
Scallops are hermaphrodite and are able to fertilise themselves to produce offspring.
Single mature adult specimens of yellow, orange and black scallops were collected and
kept in separate tanks of seawater until they produced young. The young were then scored
for shell colour. The results were as follows:
yellow scallop – 25 yellow and 8 black
orange scallop – 31 orange and 9 black
black scallop – 27 black
(a) Explain the results from the orange and black scallops, using the symbols given.
[6]
(b) Orange scallops are more valued for human consumption.
Describe how a marine biologist could produce a pure-breeding line of orange scallops
for commercial exploitation using the offspring from the single orange scallop.
[2]
[Total: 8]
UCLES 2007 9700/4/SP07 final [Turn over
PPMMTT
Question
Biology
CAIE2023
In pea plants, tall (T) is dominant over dwarf (t), and yellow seeds (Y) is dominant over green (y). Two heterozygous tall plants with yellow seeds are crossed.
(a) Write the genotypes of the parent plants.
(b) Construct a Punnett square to show the possible offspring genotypes.
(c) State the phenotypic ratio expected in the offspring.
(d) Explain what is meant by the term independent assortment.