ICAR AIEEA PG 2024 - Plant Sciences

विस्तृत व्याख्या:

Inheritance and Pedigree Analysis in Humans (मानव में वंशागति):

• X-linked traits (X-सहलग्न लक्षण): In human males ($XY$), who are hemizygous for the X chromosome, any allele on the X chromosome (whether dominant or recessive) is immediately expressed in the phenotype because there is no homologous counterpart on the Y chromosome. Furthermore, X-linked traits display characteristic criss-cross inheritance (father to daughter to grandson), making them readily distinguishable and much easier to identify.
• Recessive autosomal traits (अप्रभावी ऑटोसोमल लक्षण): These require two copies of the mutant allele (homozygosity) to be expressed phenotypically, often skip multiple generations silently via unaffected heterozygous carriers, and are much harder to track and identify without extensive pedigree and consanguinity data.

विस्तृत व्याख्या:

Non-disjunction (अवियोजन):

• Non-disjunction is the failure of homologous chromosomes to separate during Meiosis I (Anaphase I) or the failure of sister chromatids to separate during Meiosis II (Anaphase II).
• Meiosis I Non-disjunction: Leads to 100% abnormal gametes ($n+1, n+1, n-1, n-1$).
• Meiosis II Non-disjunction: Leads to 50% abnormal gametes ($n+1, n-1$) and 50% normal gametes ($n, n$).
• Fertilization of these abnormal gametes leads to aneuploidy (e.g., trisomy $2n+1$ such as Down syndrome or monosomy $2n-1$ such as Turner syndrome).
• Translocation and Inversion are structural chromosomal aberrations, while Insertions are gene-level mutations.

Correct Answer: Option 3 (Non-disjunction).

विस्तृत व्याख्या:

Classification of Aneuploids (असुगुणिता का वर्गीकरण):

• Aneuploidy involves the loss or addition of one or more individual chromosomes from the normal complement ($2n$):

• Hyperploidy (हाइपरप्लॉइडी / अधिगुणिता): When one or more chromosomes are added / overrepresented:
  • Trisomic: $2n + 1$

• Double Trisomic: $2n + 1 + 1$
• Tetrasomic: $2n + 2$

• Hypoploidy (हाइपोप्लॉइडी / अल्पगुणिता): When one or more chromosomes are lost / underrepresented:
  • Monosomic: $2n - 1$

• Nullisomic: $2n - 2$
• Polyploidy: Numerical change involving complete sets of chromosomes ($3n, 4n, 6n$).
• Alloploid: Polyploid containing genomes derived from two or more distinct species.