Time: 3 Hours | Full Marks: 70 | Pass Marks: 28
UNIT-I
Question 1 (Answer any two) [2x2=4]
(a) State Mendel's law of segregation.
Mendel's Law of Segregation states that during the formation of gametes, the two alleles for a trait separate or segregate from each other so that each gamete carries only one allele for each gene.
(b) Differentiate between incomplete dominance and co-dominance.
| Feature | Incomplete Dominance | Co-dominance |
|---|---|---|
| Definition | Neither allele is completely dominant; the phenotype is a blend. | Both alleles are equally expressed in the phenotype. |
| Example | Pink flowers in 4 o'clock plant (Red x White). | ABO Blood Groups (A and B alleles). |
(c) What is pleiotropy? Cite an example of the phenomenon.
Pleiotropy occurs when a single gene influences multiple, seemingly unrelated phenotypic traits
Question 2 (Answer any one) [10]
(a) What is meant by multiple allelism? What are the characteristic features of multiple allelic genes? Discuss multiple allelic inheritance of ABO blood grouping system in man. Add a brief note on lethal alleles. [2+2+4+2=10]
Multiple Allelism: The presence of more than two alleles for a single gene locus in a population
.Characteristics:
ABO Blood Grouping: Controlled by the gene 'I' which has three alleles: IA, IB, and i
. IA and IB are co-dominant, while i is recessive to both. Combinations result in four phenotypes: A (IAIA or IAi), B (IBIB or IBi), AB (IAIB), and O (ii).Lethal Alleles: Alleles that cause the death of the organism that carries them
. They are usually a result of mutations in essential genes.(b) What is epistasis? How does epistasis differ from dominance? Discuss supplementary gene interactions with suitable illustration. [2+2+6=10]
Epistasis: A phenomenon where the effect of one gene (epistatic gene) masks or modifies the expression of another gene (hypostatic gene) at a different locus
.Difference from Dominance: Dominance involves interaction between alleles at the same locus, whereas epistasis involves interaction between genes at different loci
.Supplementary Gene Interaction: Occurs when the dominant allele of one gene produces a character on its own, but the dominant allele of a second gene cannot produce its own character unless the first gene is present. In Labrador Retriever coat color, the 9:3:4 ratio is a classic illustration.
UNIT-II
Question 3 (Answer any two) [2x2=4]
(a) What is linkage?
Elucidate.Linkage is the tendency of genes located close together on the same chromosome to be inherited together during meiosis
.(b) Define crossing-over.
Crossing-over is the exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis
. (c) Who coined the term 'mutation'? Define point mutation.The term 'mutation' was coined by Hugo de Vries
. A point mutation is a genetic mutation where a single nucleotide base is changed, inserted, or deleted from a DNA or RNA sequence.Question 4 (Answer any one) [10]
(a) What is genetic recombination? Discuss the mechanism of crossing-over and the theories related to the phenomenon. [2+4+4=10]
Genetic Recombination: The process of forming new allelic combinations in offspring by exchanges between genetic material
.Mechanism of Crossing-over:
(b) What are chromosomal aberrations? Discuss types of gene mutations. What is tautomerization? [1+7+2=10]
Chromosomal Aberrations: Structural or numerical changes in chromosomes
. Gene Mutations: Include base substitutions (transitions/transversions) and frameshift mutations (insertions/deletions). Tautomerization: A chemical process where a base shifts to an alternative structural form, leading to mispairing during DNA replication.UNIT-III
Question 5 (Answer any two) [2x2=4]
(a) How many types of sex-chromosomes in human? What is Turner's syndrome?Humans have two types of sex chromosomes: X and Y
. Turner's syndrome is a chromosomal condition in females (45, X) caused by the partial or complete absence of one X chromosome.(b) What is meant by cris-cross pattern of inheritance?
It is a type of X-linked inheritance where a trait is passed from a father to his grandsons through his daughters (e.g., color blindness)
.(c) What is extra-chromosomal inheritance?
Inheritance of traits controlled by genes found in the cytoplasm (mitochondria or chloroplasts) rather than the nucleus; often shows maternal inheritance
.Question 6 (Answer any one) [10]
(a) Discuss sex-chromosomal mechanism of sex determination. Add a note on genic balance mechanism. [6+4=10]
Common mechanisms include XX-XY (Mammals) and ZZ-ZW (Birds)
. The Genic Balance Mechanism (Calvin Bridges) suggests sex is determined by the ratio of X chromosomes to the sets of autosomes (X/A ratio).(b) Holandric genes, X-linked inheritance in humans, and sex-influenced vs sex-limited genes. [1+6+3=10]
Holandric Genes: Genes located on the Y chromosome passed exclusively from father to son
. Sex-influenced traits are autosomal but expressed differently based on sex (e.g., baldness), while Sex-limited traits appear in only one sex (e.g., milk production).UNIT-IV
Question 7 (Answer any two) [2x2=4]
(a) What is nucleic acids and who first isolated it?
Polymers of nucleotides (DNA/RNA) carrying genetic info
. First isolated by Friedrich Miescher.(b) Differentiate between B-DNA and Z-DNA.
| Feature | B-DNA | Z-DNA |
|---|---|---|
| Helix Sense | Right-handed | Left-handed |
| Sugar-Phosphate Backbone | Regular | Zig-zag |
(c) What is non-genetic RNA and what are its types?
RNA not acting as the primary genetic material
. Types: mRNA, tRNA, and rRNA.Question 8 (Answer any one) [10]
(a) What is nucleotide? Discuss double helical structural model of DNA. [2+8=10]
Nucleotide: Building block of DNA/RNA consisting of a sugar, phosphate, and nitrogenous base
. The Watson-Crick Model describes DNA as a double helix with antiparallel strands, complementary base pairing (A=T, G≡C), and major/minor grooves.(b) Chemical composition of DNA and RNA. Differentiate between nucleoside and nucleotide. [8+2=10]
DNA uses deoxyribose and thymine; RNA uses ribose and uracil. A nucleoside is a base + sugar, while a nucleotide is a nucleoside + phosphate group.
UNIT-V
Question 9 (Answer any two) [2x2=4]
(a) Semi-conservative mode of DNA replication.
Each new DNA molecule consists of one original (parental) strand and one newly synthesized strand
.(b) What is transcription?
The process of copying a segment of DNA into RNA (mRNA) by the enzyme RNA polymerase
.(c) What is Wobble hypothesis?
Proposed by Crick; it states that the 3rd base of a codon can pair non-standardly with the 1st base of an anticodon, allowing one tRNA to recognize multiple codons
.Question 10 (Answer any one) [10]
(a) Enzymes in DNA replication and mechanism in prokaryotes. [4+6=10]
Enzymes: Helicase, Primase, DNA Polymerases, Ligase, Topoisomerase
. Mechanism: Includes Initiation at 'oriC', Elongation (leading/lagging strands with Okazaki fragments), and Termination.(b) Features of genetic code and mechanism of translation in prokaryotes. [4+6=10]
Features: Triplet, Universal, Degenerate, Non-overlapping, Comma-less
. Translation: Involves Initiation (forming 70S complex), Elongation (peptide bond formation), and Termination (release factors).