Page 35 - CB1.3 Genetic Varation sciPAD
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CB 1.3 GENETIC VARIATION
TRACKING GENES
Pure Breeding
If an organism is ‘pure breeding’ it means that it is homozygous for
the allele being studied, i.e. all of the offspring produced by either
self fertilisation (in plants), or by breeding with others who are
identical for this characteristic, show the same phenotype as the
parent.
1. A plant geneticist produced two lines of pea plants that
were pure breeding for flower colour. One line produced
purple flowers; the other, white flowers. The geneticists found
that purple flowers (P) were dominant to white flowers (p).
(a) Define the term ‘pure breeding’.
(b) Complete the Punnett square below to show the possible genotypic and phenotypic
ratios of the offspring produced when two pure-breeding purple-flowering plants
are crossed.
Genotype of parent 1: Genotype of parent 2:
Genotypic ratio of the offspring:
Phenotypic ratio of the offspring:
2. Complete the Punnett square below to show the possible genotypic and phenotypic
ratios of the offspring produced when a pure-breeding purple-flowering plant is crossed
with a pure-breeding white-flowering plant.
Genotype for purple flowered: Genotype for white flowered:
Genotypic ratio of the offspring:
Phenotypic ratio of the offspring:
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