Genetics And Plant Breeding - Study Mode

[#416] Which of the following is Top cross
Correct Answer

(B) Inbred × O.P var

Explanation

Solution: From the given options, Inbred × O.P var is the Top cross. It refers to the use of highly inbred males to the females of the base population or non-inbred population. The top cross is a cross between a superior or purebred male and inferior female stock to improve the average quality of the progeny.

[#417] Match the following columns: Column I (Relations) Column II (Cell Organelles) a. Protein synthesis 1. Lysosome b. Golgi apparatus 2. Nucleosome c. RNA synthesis 3. Dictyosome d. Sucidal bags 4. Ribosome
Correct Answer

(D) a-4, b-3, c-2, d-1

Explanation

Solution: a. Protein synthesis occurs in Ribosomes. The ribosome is universally responsible for synthesizing proteins by translating the genetic code transcribed in mRNA into an amino acid sequence. b. Golgi apparatus is Dictyosome. In plant cells, the Golgi apparatus consists of several separate units called dictyosomes. c. RNA synthesis occurs in Nucleosomes. In cells, RNA elongation by RNAPII is stalled at multiple sites within a nucleosome. d. Suicidal bags are Lysosome. It is a membrane-bound organelle found in many animal cells. De Duve had termed the Lysosomes, the "suicide bags" or "suicide sacs" of the cells, for their hypothesized role in apoptosis.

[#418] The 'pure line' theory was proposed by
Correct Answer

(B) Johannsen

Explanation

Solution: The 'pure line' theory was proposed by Johannsen. Wilhelm Johannsen was a Danish pharmacist, botanist, plant physiologist, and geneticist.
He is best known for coining the terms gene, phenotype, and genotype, and for his 1903 "pure line" experiments in genetics. A pure line is the progeny of a single self-fertilized homozygous plant.

[#419] The C 4 -plants are more efficient than C 3 -plants because
Correct Answer

(D) They lack photorespiration

Explanation

Solution: The C 4 plants are more efficient than the C 3 plants because they lack photorespiration. C 4 plants including maize, sugarcane, and sorghum avoid photorespiration by using another enzyme called PEP during the first step of carbon fixation. This step takes place in the mesophyll cells that are located close to the stomata where carbon dioxide and oxygen enter the plant. Photorespiration happens in C 3 plants when the CO 2 concentration drops to about 50 ppm. The key enzyme that accomplishes the fixing of carbon is rubisco, and at low concentrations of CO 2 , it begins to fix oxygen.

[#420] When chiasma frequency is 100%, the percentage of crossing over is
Correct Answer

(A) 50%

Explanation

Solution: When chiasma frequency is 100%, the percentage of crossing over is 50%. A chiasma is the point of contact, the physical link, between two chromatids belonging to homologous chromosomes. At a given chiasma, an exchange of genetic material can occur between both chromatids and is called a chromosomal crossover. When chiasma is organized in between two gene loci, only 50% of meiotic products shall be crossovers and 50% non-crossovers. Thus, the chiasma frequency is twice the frequency of cross-over products, therefore, when the chiasma frequency is 100%, the percentage of crossing-over is halved i.e. 50%.