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Question

A green stemmed rose plant denoted by GG and a brown stemmed rose plant denoted by gg are allowed to undergo a cross with each other.
(a) List your observations regarding-(i) Colour of the stem in their F, progeny, (ii) Percentage of brown stemmed plants in F2 progeny if F1 plants are self-pollinated, (iii) Ratio of GG and Gg in the F2 progeny.
(b) Based on the findings of this cross, what conclusion can be drawn?


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Solution

Mendel:

  1. Mendel was an austrian monk.
  2. Between 1856-1863, Mendel conducted the hybridization experiments on the garden peas.
  3. Mendel experimented on a pea plant and considered 7 main contrasting traits in the plants.
  4. Then, he conducted the experiments to determine the inheritance laws.

Law of dominance:

  1. When parents with pure, contrasting traits are crossed together, only one form of trait appears in the next generation. The hybrid offsprings will exhibit only the dominant trait in the phenotype.
  2. Law of dominance is known as the first law of inheritance.

A. (i) Green is the dominant trait and in the F1 progeny, only the dominant trait has expressed The color of the stem in the F1 progeny will be green.

(ii) If F1 plants are self-pollinated, the ratio of brown stemmed plants to green stemmed plants in the F2 progeny is 1:3. So the ratio of brown stemmed plants in F2 progeny is 25%.

(iii) 1:2:1

GG and Gg are both the green pods that means the G is dominant and g is the recessive allele. Also for example: when a test cross between the two organism having the same genotype will take place . So the Gg for the heterozygous dominant trait will all just result in the offspring having the genotypes as : GG, Gg and so gg .Therefore here in this the ratio would be 1:2:1.

(b) The conclusion is that both the gametes are showing their expression in the F2 generation because we are getting a 1:2:1 ratio of the monohybrid cross. We can see that both the laws of Mendel have been used in this case which is low of dominance and law of segregation.


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