A purebred black-faced ram is crossed with a purebred white-faced ewe - NSC Agricultural Sciences - Question 4 - 2016 - Paper 2
Question 4
A purebred black-faced ram is crossed with a purebred white-faced ewe. B represents the ram's face colour, which is dominant over the white face colour of the ewe.
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Worked Solution & Example Answer:A purebred black-faced ram is crossed with a purebred white-faced ewe - NSC Agricultural Sciences - Question 4 - 2016 - Paper 2
Step 1
4.1.1 Write down the genotype of parent B.
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Answer
The genotype of parent B, being a purebred white-faced ewe, is homozygous recessive: bb.
Step 2
4.1.2 Indicate whether parents A and B are homozygous or heterozygous.
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Answer
Parent A (black-faced ram) is heterozygous (Bb), while parent B (white-faced ewe) is homozygous (bb).
Step 3
4.1.3 Give a reason for the answer to QUESTION 4.1.2.
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Answer
Parent A is heterozygous because it possesses one dominant and one recessive allele, while parent B is homozygous recessive, having two identical recessive alleles for the white face.
Step 4
4.1.4 Identify the phenotype in the F2 generation, as represented by F, G and H.
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Answer
The phenotypes in the F2 generation are as follows: F is black-faced, G is black-faced, and H is white-faced.
Step 5
4.1.5 Indicate the genotypic and phenotypic ratio in the F2 generation.
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Answer
The genotypic ratio in the F2 generation is 1:2:1 (1 BB: 2 Bb: 1 bb), while the phenotypic ratio is 3:1 (3 black-faced: 1 white-faced).
