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Plant 3 is tall and has a black stem - VCE - SSCE Biology - Question 31 - 2014 - Paper 1
Question 31
Plant 3 is tall and has a black stem. The phenotypes of the parents of plant 3 are unknown. To determine the genotype of plant 3, it is best to cross it with a plant... show full transcript
Worked Solution & Example Answer:Plant 3 is tall and has a black stem - VCE - SSCE Biology - Question 31 - 2014 - Paper 1
Step 1
To determine the genotype of plant 3, it is best to cross it with a plant that is of a dwarf height and red stem colour.
Answer
To ascertain the genotype of plant 3, which has a tall height and black stem, we need to perform a test cross. A test cross involves crossing the plant with a homozygous recessive plant for the traits in question.
Given that plant 3 exhibits a tall phenotype (which could be heterozygous tall or homozygous tall) and a black stem (which may also be heterozygous or homozygous), crossing it with a dwarf height and red stem colour plant, a recessive phenotype for both traits, will provide clarity on the genotype.
If any offspring exhibit the dwarf phenotype, this confirms that plant 3 must be heterozygous for height. Conversely, if all offspring are tall, we can conclude that plant 3 is homozygous.
Similarly, for stem colour, the appearance of any red-stemmed offspring would indicate that plant 3 is heterozygous for stem colour. This approach will definitively reveal the genotype of plant 3.