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Assertion (A):
The F1 hybrid RrYy produces four types of gametes (RY, Ry, rY, ry), each with 25 per cent frequency.
Reason (R):
This 1:1:1:1 gamete production ratio demonstrates that the segregation of the R/r gene pair is independent of the segregation of the Y/y gene pair.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Pedigree analysis is a crucial tool in human genetics to trace the inheritance of specific traits or diseases.
Reason (R):
Since control crosses are not possible in humans, studying the family history provides the necessary alternative data to understand inheritance patterns.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Mendelian disorders are determined by alteration or mutation in a single gene, traceable by pedigree analysis.
Reason (R):
Chromosomal disorders are caused due to the absence or excess or abnormal arrangement of one or more whole chromosomes.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Sutton and Boveri noted that the pairing and separation of a pair of chromosomes would lead to the segregation of the factors they carried.
Reason (R):
This parallel behavior provided the physical basis for Mendel's principles, forming the foundation of the Chromosomal Theory of Inheritance.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The $F_2$ phenotypic ratio 9:3:3:1 in a dihybrid cross validates the Law of Independent Assortment.
Reason (R):
This ratio is mathematically derived as a combination series of the 3:1 ratio for each character, showing independent segregation of traits.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Drosophila melanogaster is highly suitable for genetic studies because it completes its life cycle in about two weeks.
Reason (R):
A short life cycle and the ability to produce a large number of progeny flies from a single mating allow for quick observation of successive generations and gathering of large data sets.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
A female becomes haemophilic only if she is homozygous recessive ($X^h X^h$).
Reason (R):
This condition is extremely rare because it requires the affected male father ($X^h Y$) to survive the late stages of life long enough to mate with a carrier female ($X^H X^h$).
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Colour blindness occurs much more frequently in males (8%) than in females (0.4%).
Reason (R):
The genes for colour blindness are located on the X chromosome, and males are hemizygous (having only one X), so they express the trait if they inherit a single recessive allele.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Mutation is a phenomenon that leads to variation in DNA, serving as a source of heritable change.
Reason (R):
In addition to recombination, mutation is another major phenomenon that leads to variation in the DNA sequences of an organism.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Genes are the units of inheritance and contain the information required to express a particular trait.
Reason (R):
These units, which Mendel called ‘factors’, are stably passed down, unchanged, from parent to offspring through the gametes.
[Principles-of-Inheritance-and-Variation] [class-xii ]
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