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Assertion (A):
In the dog flower (*Antirrhinum sp.*), the F1 hybrid from a cross between red (RR) and white (rr) parents is pink.
Reason (R):
The phenotype of the F1 generation is intermediate because the allele R is not completely dominant over the allele r, demonstrating incomplete dominance.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Human ABO blood grouping is a good example of co-dominance.
Reason (R):
When the alleles $I^A$ and $I^B$ are present together in a person, they both express their own types of sugars simultaneously.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The phenotype of a polygenic trait reflects the additive contribution of each allele.
Reason (R):
Polygenic inheritance is generally controlled by three or more genes and takes into account the influence of the environment.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Phenylketonuria is a pleiotropic disease resulting in mental retardation and reduction in hair and skin pigmentation.
Reason (R):
The underlying mechanism of pleiotropy is the effect of a single gene on multiple metabolic pathways which contribute towards different phenotypes.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The X body discovered by Henking in insects was later identified as the X-chromosome.
Reason (R):
The X-chromosome is involved in the determination of sex, and 50 per cent of the sperm produced in XO type insects receive this structure.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
T.H. Morgan observed a significant deviation from the expected 9:3:3:1 ratio in dihybrid crosses of *Drosophila* involving sex-linked genes.
Reason (R):
Genes located on the same chromosome showed physical association, described as linkage, which prevented independent segregation.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The distance between two genes on the same chromosome can be measured by the frequency of recombination between them.
Reason (R):
Genes that are very tightly linked show a very low recombination percentage, while loosely linked genes show higher recombination.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
Thalassemia is considered a qualitative problem, resulting in the synthesis of an incorrectly functioning globin molecule.
Reason (R):
Sickle-cell anaemia is a quantitative problem because it results from the reduced rate of synthesis of globin chains.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
The sex of a human child is determined by the genetic makeup of the sperm that fertilizes the ovum.
Reason (R):
Females produce only X-carrying ova, while males produce 50 per cent X-carrying sperm and 50 per cent Y-carrying sperm.
[Principles-of-Inheritance-and-Variation] [class-xii ]
Assertion (A):
In honey bees, male drones are haploid, having 16 chromosomes.
Reason (R):
Males develop from unfertilised eggs by means of parthenogenesis and thus do not have a father.
[Principles-of-Inheritance-and-Variation] [class-xii ]
This Page Score: 0/40