Assertion (A): Genes which code for a pair of contrasting traits are known as alleles. Reason (R): Alleles are slightly different forms of the same gene.
A defines alleles. R explains that alleles are different forms of the same gene. The definition (R) supports the role of alleles (A) in coding for contrasting traits.
Question 502 of 519
📘 CLASS XII
Assertion (A): The Punnett Square is a graphical representation used to calculate the probability of all possible genotypes of offspring in a genetic cross. Reason (R): The Punnett Square was developed by British geneticist, Reginald C. Punnett.
A is True: The Punnett Square is a graphical tool for calculating genotype probability. R is True: It was developed by Reginald C. Punnett. R is a historical fact and does not explain the function described in A.
Question 503 of 519
📘 CLASS XII
Assertion (A): A heterozygous monohybrid plant (Tt) produces two kinds of gametes, T and t, with equal proportion. Reason (R): The segregation of alleles is a random process, giving a 50 per cent chance of a gamete containing either allele.
A is the result of the Law of Segregation for a heterozygote. R explains that the process is random and that 50% probability is the measurable consequence of that randomness.
Question 504 of 519
📘 CLASS XII
Assertion (A): In the F2 generation of a monohybrid cross, 3/4th of the plants are Tall (phenotype). Reason (R): The Tall plants consist of 1/4th homozygous dominant (TT) and 1/2 heterozygous (Tt) genotypes.
A is the phenotypic ratio observed in F2. R provides the precise genotypic breakdown (1/4 TT + 1/2 Tt) that sums up to the total Tall phenotype (3/4th) due to dominance.
Question 505 of 519
📘 CLASS XII
Assertion (A): When Mendel crossed a plant with yellow, round seeds (RRYY) and green, wrinkled seeds (rryy), the F1 generation (RrYy) had yellow and round seeds. Reason (R): Yellow colour was dominant over green, and round shape was dominant over wrinkled.
The F1 phenotype (A) is explained by the Law of Dominance (R), where the dominant alleles mask the recessive alleles.
Question 506 of 519
📘 CLASS XII
Assertion (A): Mendel’s Law of Independent Assortment holds true for genes located far apart on the same chromosome. Reason (R): Distantly located genes, due to recombination, assort independently.
A describes a condition where the law holds. R explains that for distantly located genes, recombination is frequent enough (approaching 50%) that they effectively assort independently.
Question 507 of 519
📘 CLASS XII
Assertion (A): The behaviour of chromosomes during meiosis parallels the behaviour of genes. Reason (R): Chromosomes as well as genes occur in pairs, and the two alleles of a gene pair are located on homologous sites on homologous chromosomes.
Sutton and Boveri noted the parallel behaviour (A). R provides the physical basis for this parallelism: both occur in pairs, and alleles reside on homologous chromosomes.
Question 508 of 519
📘 CLASS XII
Assertion (A): Thomas Hunt Morgan worked with Drosophila melanogaster to provide experimental verification of the Chromosomal Theory of Inheritance. Reason (R): Morgan observed that the genes for yellow body and white eyes did not segregate independently of each other.
A is True: Morgan verified the chromosomal theory using Drosophila. R is True: He observed that these specific genes showed non-independent segregation (linkage). R is a specific finding from the overall research program (A), but not the reason Morgan chose to undertake the verification work.
Question 509 of 519
📘 CLASS XII
Assertion (A): Morgan coined the term linkage to describe the physical association of genes on a chromosome. Reason (R): He coined the term recombination to describe the generation of non-parental gene combinations.
A is True: Morgan defined linkage as physical association. R is True: Morgan defined recombination as the generation of non-parental gene combinations. Both are true definitions provided by Morgan but are distinct concepts.
Question 510 of 519
📘 CLASS XII
Assertion (A): Grasshopper is an example of the XO type of sex determination. Reason (R): In grasshoppers, males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.
A states the mechanism in grasshoppers. R describes the chromosomal composition (male XO, female XX) that defines this type of sex determination.
