Genetics Plant Breeding

Step 1: Define co-dominance.
Co-dominance occurs when two alleles in a heterozygote are both expressed fully and equally without blending.
Step 2: Classic example.
The best example is the ABO blood group system in humans, where IA and IB alleles are co-dominant, producing AB blood group.
Step 3: Check options.
- Co-dominance: Correct, both alleles are expressed.
- Partial dominance: Wrong, here heterozygote shows intermediate phenotype.
- Pseudo dominance: Wrong, occurs when recessive allele is expressed due to deletion of dominant allele.
- Over dominance: Wrong, heterozygote expresses a trait stronger than either homozygote.
Step 4: Conclusion.
Hence, when both alleles of a gene are fully expressed in heterozygotes, it is called Co-dominance.

Step 1: Event A - Double-strand breaks appear.
This is an early meiotic recombination event seen during pachytene. → (A - I)
Step 2: Event B - Joint molecules recovered.
This occurs towards the end of zygotene, where chromosomes align and crossing over begins. → (B - II)
Step 3: Event C - Recombinant DNA molecules recovered.
New recombinant structures form during beginning of zygotene. → (C - IV)
Step 4: Event D - Double-strand breaks disappear.
At the end of recombination process, seen in diplotene. → (D - III)
Step 5: Conclusion.
The correct matching is: A - I, B - II, C - IV, D - III.

Step 1: Understanding autotetraploid.
An autotetraploid is a polyploid organism with four sets of chromosomes derived from a single species. It is usually developed for increased biomass and forage quality.
Step 2: About 'Pusa Giant'.
‘Pusa Giant’ is a famous variety of berseem (Trifolium alexandrinum), a widely cultivated fodder crop in India. It was developed as an autotetraploid to improve yield and adaptation.
Step 3: Checking options.
- Bean: No such autotetraploid called Pusa Giant.
- Berseem: Correct, ‘Pusa Giant’ is an autotetraploid variety.
- Tomato: Pusa varieties exist, but not as an autotetraploid named ‘Pusa Giant’.
- Egg plant: No such autotetraploid variety named Pusa Giant.
Step 4: Conclusion.
Thus, ‘Pusa Giant’ is an autotetraploid of berseem.

Step 1: Recall Y-linked inheritance.
Genes present on the Y chromosome are transmitted exclusively from father to son, as only males inherit the Y chromosome.
Step 2: Transmission logic.
- Sons inherit the Y chromosome from their father, so all sons will receive Y-linked genes.
- Daughters inherit the X chromosome from their father, not the Y. Hence, daughters cannot inherit Y-linked traits.
Step 3: Checking the options.
- All sons: Correct.
- All daughters: Wrong, daughters inherit X only.
- Half of sons: Wrong, all sons inherit Y.
- Half of daughters: Wrong, daughters never inherit Y.
Step 4: Conclusion.
Thus, a man carrying a Y-linked gene transmits it to all his sons.

Step 1: Recall Snyder’s test.
Snyder’s ratio is a method in population genetics used to test equilibrium conditions for dominant and recessive gene frequencies.
Step 2: Ratio definition.
It specifically compares expected ratios of genotypes using allele frequency . The two ratios derived are: and .
Step 3: Eliminate wrong options.
Options (2), (3), and (4) contain incorrect denominator or exponent terms, making them invalid for Snyder’s test.
Step 4: Conclusion.
Thus, the correct two population ratios are and .

Step 1: Define QTL mapping.
QTL = Quantitative Trait Loci. These are genomic regions associated with quantitative traits such as height, yield, or disease resistance.
Step 2: Historical note.
In 1923, Sax was the first to demonstrate the association between a Mendelian marker gene and a quantitative trait, which laid the foundation of QTL mapping.
Step 3: Checking options.
- Stern → Known for genetic recombination studies, not QTL.
- Sax → Correct, 1923 work linked seed coat color and seed size in beans.
- Mather → Worked on polygenic inheritance.
- Galton → Studied biometrics and heredity but not QTL mapping.
Step 4: Conclusion.
Thus, QTL mapping was first described by Sax in 1923.