(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
. An example is Sickle Cell Anemia, where a single mutation in the hemoglobin gene affects red blood cell shape, causes anemia, and provides resistance to malaria.(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.
(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.(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.(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
.(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).(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.(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.
(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
.(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).