Inheritance and disorders
Read the passage carefully and answer the given questions.
Mutation is a phenomenon which results in alteration of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism. In haemophilia, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding. The heterozygous female for haemophilia may transmit the disease to sons. The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic. Sickle-cell anaemia is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene. The disease is controlled by a single pair of allele, HbA and HbS. The chromosomal disorders on the other hand are caused due to absence or excess or abnormal arrangement of one or more chromosomes. Failure of segregation of chromatids during cell cycle results in the gain or loss of a chromosome, called aneuploidy.
The pattern of inheritance of Mendelian disorders can be traced in a family by:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Pedigree analysis
(1) Pedigree analysis — Correct. A pedigree is a family tree that shows who in the family has a trait. By studying it we can tell whether a Mendelian disorder is dominant or recessive, and whether it is linked to a sex chromosome.
(2) Epistasis — Incorrect. This is an interaction in which one gene masks the effect of another gene. It is not a method of tracing inheritance.
(3) Mutation — Incorrect. This is a change in the genetic material. It is the cause of a disorder, not a way of tracing it.
(4) Polygenic Inheritance — Incorrect. This is the control of one trait by many genes. Mendelian disorders are controlled by a single gene.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Mendelian Disorders –
