Genetics

To test if a dominant trait is heterozygous, an hybrid is crossed with a homozygous recessive (test cross). The resulting 1:1 phenotypic ratio confirms heterozygosity of the dominant parent.

The cross between a heterozygous round and yellow seeded pea plant with another pea plant showing wrinkled and heterozygous yellow results in eight phenotypes, with the genotypic ratio of 1:2:1:2:1:2.

The statement "One codon codes one amino acid" is incorrect because some codons can code for more than one amino acid due to the redundancy of the genetic code.

In a monohybrid cross involving homozygous tall and dwarf plants, the F2 generation would show a 1:1 ratio of homozygous tall to dwarf plants. This is due to the segregation of alleles.

The assertion is correct as cistron refers to a segment of DNA coding for a polypeptide. However, the reason is incorrect because monocistronic genes are present in eukaryotes and are not split.

- Exonucleases — remove nucleotides from {ends} of DNA.
- Endonucleases — cut within DNA at specific sites (used in genetic engineering).
Other options list incorrect or irrelevant enzyme types.

Step 1: Understand the Dihybrid Cross In a typical Mendelian dihybrid cross (e.g., ), the phenotypic ratio in the generation is: This corresponds to: \begin{itemize} \item 9 parts: both dominant traits (A-B-) — Parental type \item 3 parts: dominant A, recessive b (A-bb) — Recombinant \item 3 parts: recessive a, dominant B (aaB-) — Recombinant \item 1 part: both recessive traits (aabb) — Parental type \end{itemize} Step 2: Determine Total Recombinant Ratio Out of total 16 parts: Step 3: Calculate Number of Recombinants Total number of progeny = 1280

- Selectable marker is not a method of transfer, it's used for selecting transformed cells.
- Disarmed pathogen vector — method using modified Agrobacterium plasmids.
- Biolistic method — gene gun, physical method.
- Microinjection — DNA injected directly into nucleus.

Step 1: Understand the concept of mutation
Mutation refers to any change in the DNA sequence. These changes can alter genes, cause variations in DNA, and can be inherited if they occur in germ cells. Step 2: Analyze each statement
- I. Alteration of genes — This is a direct result of mutation.
- II. Variation in DNA — Mutations cause DNA sequence variation.
- III. Heritable change in genotype and phenotype — Mutations can be passed on and may alter phenotype. Step 3: Conclusion
All three statements describe aspects of mutation correctly.

Step 1: Identify the parental genotypes and F1 generation.
The parents are described as "pure round and yellow" and "wrinkled and green".
Let's assign alleles:
Round (R) is dominant over wrinkled (r)
Yellow (Y) is dominant over green (y)
So, the parental genotypes are:
Pure Round and Yellow: RRYY
Wrinkled and Green: rryy
The F1 generation (obtained by crossing RRYY x rryy) will have the genotype RrYy. Step 2: Determine the F2 generation genotypes for the dihybrid cross.
The F2 generation is obtained by self-crossing the F1 generation (RrYy x RrYy). This is a standard Mendelian dihybrid cross. The genotypic ratio of the F2 generation is:
1 RRYY : 2 RRYy : 1 RRyy :
2 RrYY : 4 RrYy : 2 Rryy :
1 rrYY : 2 rrYy : 1 rryy
Step 3: Identify the genotypes that result in "wrinkled : yellow coloured seed" phenotype.
The question asks for the ratio of genotypes that correspond to the "wrinkled : yellow coloured seed" phenotype.
A wrinkled phenotype is represented by the homozygous recessive genotype 'rr'.
A yellow coloured seed phenotype is represented by 'YY' or 'Yy' (since yellow is dominant). Combining these, the genotypes in the F2 generation that will exhibit the wrinkled yellow phenotype are:
rrYY (wrinkled and yellow)
rrYy (wrinkled and yellow)
Step 4: Determine the ratio of these genotypes.
From the F2 genotypic ratio listed in Step 2:
The proportion of rrYY is 1.
The proportion of rrYy is 2.
Therefore, the ratio of the genotypes (rrYY : rrYy) for wrinkled yellow coloured seeds is 1 : 2.
Step 5: Compare with the given options.
The calculated ratio of 1:2 matches option (2). The final answer is .

Step 1: Understanding the definition
Pleiotropy refers to the condition where a single gene influences multiple phenotypic traits. This happens when the gene product affects more than one aspect of physiology or development. Step 2: Analyze each option
- Codominance: Both alleles express themselves equally in a heterozygote, but do not cause multiple phenotypic effects.
- Incomplete dominance: One allele does not completely dominate the other, resulting in an intermediate phenotype.
- Pleiotropy: Correct — a single gene affects multiple traits.
- Independent Assortment: Refers to the segregation of genes on different chromosomes during gamete formation. Step 3: Conclusion
The description fits pleiotropy most accurately.

- DNA polymerase adds nucleotides in 5′→3′ direction, always.
- Template may be 3′→5′, but synthesis happens in 5′→3′.
- Hence, option (2) is incorrect.