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Assertion (A):
To determine the genotype of a tall F2 plant, Mendel crossed it with the dwarf parent, calling this a test cross.
Reason (R):
The progenies of the test cross can be easily analysed to predict the genotype of the test organism, distinguishing between TT and Tt compositions.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Mendel’s work gained greater credibility due to his use of statistical analysis and large sampling sizes.
Reason (R):
Confirmation of his inferences from experiments on successive generations proved that his results pointed to general rules of inheritance.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
A true-breeding pea line, established through continuous self-pollination, shows stable trait inheritance for several generations.
Reason (R):
Mendel selected true-breeding lines to ensure the parental traits were homozygous and consistent before starting his hybridisation experiments.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The phenotype of the F1 heterozygote (Tt) in a monohybrid cross is exactly like the TT parent in appearance.
Reason (R):
In a pair of dissimilar factors, one (T, the dominant factor) dominates the other (t, the recessive factor), so only the dominant trait is expressed in F1.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The starch grain size in heterozygous pea seeds (Bb) is intermediate, showing incomplete dominance for this phenotype.
Reason (R):
If seed shape is chosen as the phenotype, the same genotype (Bb) results in a round shape, demonstrating complete dominance.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The modified allele of a gene is generally the recessive allele.
Reason (R):
This is because the modified allele often produces a non-functional enzyme or no enzyme at all, making the phenotype dependent solely on the expression of the unmodified (dominant) allele.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Thalassemia is a qualitative problem, while sickle-cell anaemia is a quantitative problem regarding haemoglobin synthesis.
Reason (R):
The former is due to the reduced rate of synthesis of globin chains, and the latter is due to the synthesis of an incorrectly functioning globin.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The severity of $\alpha$ Thalassemia is related to the number of genes that are mutated or deleted.
Reason (R):
$\alpha$ Thalassemia is controlled by two closely linked genes (HBA1 and HBA2) on chromosome 16, resulting in a total of four genes per individual.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Polyploidy, resulting in an increase in a whole set of chromosomes, is often seen in plants but is rare in animals/humans.
Reason (R):
Polyploidy is caused by the failure of cytokinesis after the telophase stage of cell division.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Aneuploidy refers to the gain or loss of a chromosome or chromosomes.
Reason (R):
This phenomenon occurs due to the failure of segregation of chromatids during the cell division cycle.
[Principles-of-Inheritance-and-Variation] [class-xii ]
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