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Assertion (A):
In Thalassemia, the severity of the disease is considered a quantitative problem.
Reason (R):
Thalassemia is caused by mutation or deletion resulting in the reduced rate of synthesis of one of the globin chains ($\alpha$ or $\beta$).
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
In honey bees, male drones do not have a father and cannot have sons.
Reason (R):
Males develop from unfertilised eggs by means of parthenogenesis and are haploid, producing sperm by mitosis.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Down’s Syndrome is a monosomy of chromosome 21.
Reason (R):
Chromosomal disorders like Down’s Syndrome are caused by aneuploidy, due to the failure of chromatid segregation during the cell division cycle.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The work of Watson and Crick on the complementary double-helical configuration of DNA was a major contribution to the field of molecular biology.
Reason (R):
The entire body of molecular biology was a consequent development aimed at understanding the structure and basis of Mendel’s ‘factors’ and genotype-to-phenotype conversion.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The Law of Independent Assortment fails for genes that are closely located on the same chromosome.
Reason (R):
Closely located genes show tight linkage, resulting in high proportions of parental combinations and limited independent assortment.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
In XO type sex determination (e.g., Grasshopper), the sperm determines the sex of the offspring.
Reason (R):
Males produce sperm either carrying the X-chromosome or lacking an X-chromosome, while all eggs contain an X-chromosome.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
In Antirrhinum (Snapdragon), the F2 phenotypic ratio is 1:2:1 (Red: Pink: White).
Reason (R):
The allele R is not completely dominant over r, which makes it possible to distinguish the heterozygous (Rr) pink phenotype from the homozygous red (RR) and white (rr).
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
In a dihybrid cross, the four genotypes of gametes (RY, Ry, rY, ry) are produced each with a frequency of 25 per cent (1/4th).
Reason (R):
This equal frequency results from the independent segregation of the R/r gene pair from the Y/y gene pair during meiosis in the F1 hybrid.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
If a woman carries the gene for colour blindness and marries a normal man, her daughters will not normally be colour blind.
Reason (R):
Colour blindness is an X-linked recessive disorder, and daughters inherit a normal X chromosome from the father, suppressing the recessive gene from the mother.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The entire body of molecular biology developed subsequent to Mendel's work.
Reason (R):
This field focused on understanding the structure of genetic material and the structural basis of genotype and phenotype conversion.
[Principles-of-Inheritance-and-Variation] [class-xii ]
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