question_answer 23)

  A across between two tall plants resulted in offspring having few dwarf plants. What would be the genotypes of both the parents?                 (a)TTandTt                          (b) Tt and Tt                       (c) TT and TT                       (d) Tt and tt

Answer:

                    (b) Tt and Tt let's use Mendel's cross of tall and dwarf pea plants as an example. The  plants of genotype Tt are self-pollinated.(both tall (T) but with dwarf (t) alleles).   The letters T and t are used to represent the alleles of the gene that determine plant height by conventions. The upper case letter (T) represents the dominant allele and the recessive allele (t) is represented by the same letter in lower case. Thus, the tall parents plants having heterozygous alleles, results in off springs which comprises of both tall and dwarf plants. For the parental cross, both the parents are true breeding plants, the tall plant is homozygous for the tall allele T, while the dwarf plant is homozygous for the dwarf allele 't'. Mendel tracked each trait through two generations. When true breeding plants were crossed to each other, this is called a parental cross and offspring comprise the first filial or F1 - generation. When the members of theF1 - generation were crossed, this produced the F2-generation or second filial generation. A cross between true breeding tall and dwarf plants of the parent generation yield phenotypically tall plants. The cross between TT and Tt is called back cross, which results into two homozygous and two heterozygous dominant gametes. The cross between Tt and tt is called testcross which results into 1:1 ratio of gametes.