Exceptions to Mendel's Law MCQ Quiz in मराठी - Objective Question with Answer for Exceptions to Mendel's Law - मोफत PDF डाउनलोड करा

Concept:

• Humans have the ABO blood grouping, which shows multiple allelism.
• Different types of red blood cells determine ABO blood grouping.
• It is an example of co-dominance.
• In co-dominance, the offspring of the F₁ generation resembles both parents.

Explanation:

• ABO blood groups are controlled by the I gene.
• The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the type of sugar is controlled by the gene.
• Gene I has three alleles I^A, I^B, and i. 
• A and B blood groups show codominance and it is dominant over the O blood group.
• A person with blood group A can have genotype I^AI^A or I^Ai, and a female with blood group AB can have the genotype I^AI^B.
• When both the genotypes are crossed together then, we get - 

or,  

• Thus, when a person having blood group A is married to a female with blood group AB their child's blood group can be A, B, or AB. But it cannot be the O blood group.

Hence, the correct option is (3) O blood group.

Concept: 

• Genes usually function or express themselves singly or individually. But many cases are known where two genes of the same allelic pair or genes of two or more different allelic pairs influence one another. This is called gene interaction and exception to Mendelian arises due to this.

• Mendel selected 7 characters that are seed shape, seed color, pod color in pea plant for carrying out hybridization experiments and to study inheritance.
• It is to be noted that the most popular example of incomplete dominance is that of flower color in Snapdragon (dog flower or Antirrhinum majus).
• True-breeding red-flowered plant (RR) was crossed with true breeding white flowered plants (rr).
• F₁ offspring (Rr) had pink flowers.
• Here one allele is incompletely dominant over another so that intermediate phenotype is produced by F₁ hybrid with respect to the parents.
• If the F₁ is made to undergo self-pollination, the plants of F₁ generation are of three types red (RR), pink (Rr) and white flowered (rr) in the ratio of 1: 2: 1.
• In heterozygous condition (Rr), the phenotypic effect of one allele is more pronounced than that of the other and mixing of both colors (red and white) results in the development of pink color.
• Therefore, the  genotype of the two plants used for hybridization is Rr.
• Option 2 is the correct answer.

Concept:​

• Genes are units of heredity.
• They carry information from one generation to the next generation.
• Dominant: The dominant trait is the trait that first appears or is visibly displayed in the organism.
• Recessive: The recessive trait is a trait that exists at the gene level, but is masked and does not manifest in the organism.

Explanation:

​Option 1:

• In codominance, two alleles express themselves independently when present together. Therefore, the offspring resembles both parents.
• According to the principle of dominance, out of the two factors of alleles representing different traits of a character, only one express itself.
• This can be observed in the ABO blood group.
• Therefore, this is the correct answer.

​Option 2:

• When one allele (variant) of a gene on one copy of a chromosome obscures or overrides the impact of another allele (variant) of the same gene on the other copy of the chromosome is known as dominance.
• Dominant refers to the first variation, and recessive to the second.
• Therefore, this is not the correct answer.

​Option 3:

• Amphidominance can be defined as the sudden appearance of a recessive phenotype in a pedigree, due to deletion of a masking dominant gene.
• The phenomenon in which a recessive allele shows itself in the phenotype when only one copy of the allele is present, as in hemizygous alleles or in deletion heterozygotes.
• Therefore, this is not the correct answer.

​Option 4:

• Pseudodominance can be defined as a phenomenon in which the inheritance of a recessive trait mimics a dominant pattern.
• Therefore, this is not the correct answer.

Concept:

• Dominant alleles are those alleles that dominate the recessive allele and are able to show their characteristics.
• Recessive alleles are those alleles that are masked by the dominant alleles and their characters are not able to observe in the F1 generation.
• The laws proposed by Mendel on the basis of the inheritance of the Monohybrid cross are-
  • Law of Dominance: According to the law of dominance, when two alleles are heterozygous for a trait, the recessive allele gets dominated by the dominant allele. As a result, the dominant characters are seen in the F1 generation. For eg: When pea plants with the dominant traits ie. round seeds (RR) are crossed with plants with recessive traits ie. wrinkled seeds (rr), the seeds in the F1 generation were found to be round (Rr).
  • Law of Segregation: According to the Law of Segregation, during meiosis there occurs segregation or separation of allele pairs (different traits of the same gene) so that they can transfer specifically to separate gametes.
• Incomplete dominance: Incomplete dominance is the condition where neither the dominant nor the recessive allele is dominant and the F1 generation will show a blend of both the allele's traits. For eg: In a cross between true-breeding red-flowered (RR) and true-breeding white-flowered plants (rr) in snapdragon or Antirrhinum sp., the F1 generation (Rr) was pink. When the F1 generation was self-pollinated with the F2 generation it resulted in the ratio of 1 (RR) Red: 2 (Rr) Pink: 1 (rr) White.

Explanation:

• Segregation of alleles is followed by this experiment as the separation of alleles resulted in different colors or traits.
• The principle of dominance is not followed by the experiment as there were no dominant characteristics observed.
• In incomplete dominance, a blend of characteristics of both dominant and recessive alleles is observed. We observed the pink color in the F1 generation due to incomplete dominance.

Statement  1)  Law of Segregation does not apply in this experiment.

Statement  2)  This experiment does not follow the Principle of Dominance.

Statement  3)  Pink color in F₁ is due to incomplete dominance.

Statement  4)  Ratio of F₂ is 1/4(red) ∶ 2/4(pink) ∶ 1/4(white)

So, the incorrect statement is Statement  1)  Law of Segregation does not apply in this experiment.