Genetic Disorders

In a pedigree chart analysis, we need to determine the genotype of 'P', who is a female showing a disease. The disease present in ‘P’ is denoted by a recessive allele 'a'. To deduce the genotype of 'P', we consider the following points:

Inheritance Pattern: A disease caused by a recessive allele will only manifest in an individual if they have two copies of the allele, i.e., they are homozygous recessive ('aa').

Pedigree Analysis: Since 'P' is suffering from the disease, she must be homozygous for the recessive allele. This means 'P' can only have the genotype 'aa'.

Conclusion: As the disease is present in 'P' and is determined by a recessive allele, her genotype is inevitably 'aa'.

Therefore, the correct genotype of 'P', given that she is affected by the recessive disease, is aa.

To correctly match List-I with List-II, we need to understand the characteristics of each term:

• Thalassemia: This is an autosomal recessive disease caused by mutations affecting hemoglobin synthesis, leading to anemia.
• Klinefelter’s syndrome: This genetic condition in males is due to the presence of an extra X chromosome, resulting in a karyotype of 47, XXY.
• Turner’s syndrome: A chromosomal disorder where a female is missing part of or an entire X chromosome, leading to a 45, XO karyotype.
• Colour blindness: A sex-linked recessive disorder typically affecting the ability to perceive certain colors correctly, most commonly red-green color blindness.

Using these descriptions, the correct matches are:

The correct answer is: (A)-(IV), (B)-(I), (C)-(III), (D)-(II)

To determine which statements are correct, we will evaluate each one based on biological principles:

(A) During incomplete dominance, the modified allele is the dominant allele: Incomplete dominance actually refers to a situation where neither allele is completely dominant over the other. Instead, the phenotype is a blend of the two alleles. Hence, statement (A) is incorrect.

(B) In polygenic inheritance, the effect of each allele is additive: Polygenic inheritance involves several genes contributing to a trait, with each allele adding a small amount to the phenotype. Thus, statement (B) is correct.

(C) A gene is called pleiotropic when it exhibits multiple phenotypic expressions: Pleiotropy occurs when one gene influences multiple phenotypic traits. Therefore, statement (C) is correct.

(D) Mutation means alteration of DNA sequence which ensures change only in the phenotype of an organism: Mutation involves changes in the DNA, but it does not guarantee a change in phenotype; it depends on many factors. Thus, statement (D) is incorrect.

Based on this analysis, the correct statements are (B) and (C) only.