Fish Genetics and Breeding- ICAR JRF/SRF 2024

• Wild-Type Allele: The allele that occurs with the highest frequency in a natural, wild population is designated as the wild type. It is typically considered the standard or baseline functional allele responsible for the typical wild phenotype.
• Mutant Allele: Any alternative form of an allele that arises through spontaneous or induced mutation and is present at a significantly lower frequency.
• nalysis:
• (Wild type): Correct. Represents the predominant, naturally occurring allele in wild populations.
• (Carrier type): Refers to heterozygous individuals carrying a recessive allele without phenotypic manifestation.
• (Mutant type): A modified allele, typically rare.
• (Semi lethal type): Allele that causes mortality in a proportion of individuals possessing it.

Correct option: (2) Wild type

• Origin of the Punnett Square:
• The Punnett square is a tabular visual representation used by geneticists to predict the frequencies of genotypes and phenotypes resulting from a genetic cross.
• It was devised in 1905 by the British geneticist Reginald Crundall Punnett (1875–1967), who was a co-founder (with William Bateson) of the Journal of Genetics.
• nalysis:
• (Reginald C. Punnett): Correct spelling of the scientist's name.
• Options 1, 2, 4: Misspelled variations of Reginald C. Punnett.

Correct option: (3) Reginald C. Punnett

• Core Components of the Replisome at a Replication Fork:
• DNA Helicase: Unwinds the double-stranded DNA helix.
• Topoisomerase (Gyrase): Relieves torsional strain and positive supercoiling ahead of the replication fork.
• RNA Primase (RNA Primer): Synthesizes short RNA oligonucleotides required by DNA polymerase to initiate chain elongation.
• $\beta$-Sliding Clamp: Ring-shaped protein homodimer that encircles DNA and tethers DNA polymerase III, ensuring high processivity.
• Single-Strand DNA-Binding Proteins (SSBs): Prevent reannealing of separated template strands.
• Translocase:
• Translocases are motor proteins involved in macromolecular transport across biological membranes (e.g., Sec translocase in bacteria, mitochondrial TIM/TOM translocases), or moving along DNA during chromatin remodeling, but are NOT part of standard replication fork elongation machinery.
• nalysis:
• (Translocase): Correct (not a constituent of the standard replication fork).

Correct option: (1) Translocase

• Aneuploidy Terminology:
• Aneuploidy involves the loss or gain of one or more individual chromosomes from the normal diploid set ($2n$):
• Nullisomy ($2n - 2$): Loss of both members of an entire homologous pair of chromosomes.
• Monosomy ($2n - 1$): Loss of a single individual chromosome.
• Trisomy ($2n + 1$): Addition of a single extra chromosome.
• Tetrasomy ($2n + 2$): Addition of an extra pair of homologous chromosomes.
• nalysis:
• (2n-2): Correct formula for nullisomy.
• (2n+1): Represents trisomy.

Correct option: (2) 2n-2

• Two-Locus Model of Scaliness in Cyprinus carpio:
• Kirpichnikov established that scale patterns in common carp are governed by two independent diallelic gene loci: $S$ (Scaliness) and $N$ (Neutral/Lethal factor):

• Scaled carp: Genotype $S-nn$ (completely covered with regular scales).
• Mirror carp: Genotype $ssnn$ (homozygous recessive at the $S$ locus; body characterized by large, scattered, irregular mirror-like scales along the lateral line and dorsal ridge).
• Line carp: Genotype $S-Nn$ (single continuous row of scales along the lateral line).
• Leather (Nude) carp: Genotype $ssNn$ (virtually devoid of scales).
  • Note: Homozygous dominant $NN$ is embryonically lethal.

• nalysis:
• (Homozygous recessive): Correct. The mirror carp phenotype is expressed when homozygous recessive ($ss$) at the scale locus.