Genetic disorders
Read the following passage carefully and answer the given questions.
Broadly, genetic disorders may be grouped into two categories – Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in the single gene. It is important to mention here that such Mendelian disorders may be dominant or recessive. By pedigree analysis one can easily understand whether the trait in question is dominant or recessive. The chromosomal disorders on the other hand are caused due to absence or excess or abnormal arrangement of one or more chromosomes. Down’s syndrome, Turner’s syndrome, Klinefelter’s syndrome are common examples of chromosomal disorders. Mutation is defined as change in the genetic material. A point mutation is a change of a single base pair in DNA. Sickle-cell anaemia is caused due to change of one base in the gene coding for beta-chain of hemoglobin. The total number of chromosomes in a normal human cell is 46 (23 pairs). Out of these 22 pairs are autosomes and one pair of chromosomes are sex chromosome. Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome(s) called aneuploidy. Failure of cytokinesis after telophase stage of cell division results in an increase in a whole set of chromosomes in an organism and this phenomenon is known as polyploidy.
Identify the incorrect fact about the pedigree analysis.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → It is an important tool for DNA sequencing and DNA fingerprinting.
Pedigree analysis is the study of how a trait is passed on in a family over several generations. The family history is drawn as a chart with standard symbols, like a family tree.
(1) Pattern of inheritance of Mendelian disorders can be traced in a family by the pedigree analysis. — Correct statement. Tracing the pattern in a family is its use.
(2) By pedigree analysis one can easily understand whether the trait is dominant or recessive. — Correct statement. The way a trait appears in the generations shows this.
(3) It is an important tool for DNA sequencing and DNA fingerprinting. — Incorrect statement. Pedigree analysis works on a family’s traits. DNA sequencing and DNA fingerprinting are separate laboratory techniques that work on the DNA itself.
(4) It can be studied on basis of important standard symbols used to depict pedigree chart. — Correct statement. A pedigree chart is drawn with standard symbols for male, female, affected person and so on.
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 –
