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    my head is broken, haha please can someone help and explain

    In garden pea plants the genes for height and
    flower colour are on different chromosomes.
    The allele T (tall) is dominant to the allele t
    (dwarf) and the allele R (purple flowers) is
    dominant to the allele r (white flowers).
    A true-breeding tall plant with purple flowers
    was crossed with a dwarf plant with white
    flowers.

    The F1 generation were self-pollinated and 64
    plants were obtained in the F2 generation.
    How many of the F2 generation would be
    expected to be tall with white flowers?

    A 36
    B 16
    C 12
    D 4
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    The F1 generation would have been all heterozygous (TtRr) since the parents were true breeding. If the F1 generation was self pollinated, it means that two heterozygous plants would interbreed, and this produces a ratio of 9:3:3:1. If 64 were produced you would divide 64 by 9+3+3+1=16 , as a tall plant with white flowers is a recombinant so it would be the 3 in the ratio. This means you would times the answer by 3.

    So 64/16=4 and 4x3=12 so C is the answer
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    (Original post by Jmeus)
    The F1 generation would have been all heterozygous (TtRr) since the parents were true breeding. If the F1 generation was self pollinated, it means that two heterozygous plants would interbreed, and this produces a ratio of 9:3:3:1. If 64 were produced you would divide 64 by 9+3+3+1=16 , as a tall plant with white flowers is a recombinant so it would be the 3 in the ratio. This means you would times the answer by 3.

    So 64/16=4 and 4x3=12 so C is the answer
    Thank u soo much for replying , your explanation is amazing, the only thing that i am not too sure about is, why are multiplying by 3?
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    Because the Tall White genotype has two possible combinations as the tall phenotype is dominant, therefore you're looking for either TTrr or Ttrr. This occurs 3 times in the crossing of the F1 generation. (its one of the 3's in the 9:3:3:1 ratio as the genotype contains a dominant allele and recessive allele).
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    (Original post by Kate117)
    Because the Tall White genotype has two possible combinations as the tall phenotype is dominant, therefore you're looking for either TTrr or Ttrr. This occurs 3 times in the crossing of the F1 generation. (its one of the 3's in the 9:3:3:1 ratio as the genotype contains a dominant allele and recessive allele).

    Ohhh ok that makes much more sense, thank you soo much for your time
 
 
 
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