NEET Biology Reproduction Genetics and Biotechnology MCQs Set 02

Answer: (d) genital herpes

Explanation:
1. Syphilis, gonorrhoea and genital warts can be treated if detected early.
2. The infections that are not completely curable are hepatitis-B, genital herpes and HIV, so the blank is genital herpes.

Teacher's Note:
1. Bacterial STIs such as syphilis and gonorrhoea respond to antibiotics.
2. Viral STIs can be managed but not completely cured.

Answer: (b) X-linked recessive genetic disorder

Explanation:
1. Colour blindness is caused by a defect in the red or green cone genes located on the X chromosome. It is recessive, so it appears more often in males, who have only one X chromosome.
2. It is a Mendelian disorder, not a chromosomal one.

Teacher's Note:
1. A carrier mother can pass the gene to her sons.
2. A colour-blind daughter needs a colour-blind father and a carrier or affected mother.

Answer: (b) 50%

Explanation:
1. The cross is \(Tt \times Tt\), which gives \(TT : Tt : tt = 1 : 2 : 1\).
2. The homozygous offspring are \(TT\) and \(tt\), that is \(\dfrac14 + \dfrac14 = 50\%\).

Teacher's Note:
1. Heterozygous offspring are 50 percent, so homozygous ones are the remaining 50 percent.
2. The phenotypic ratio would be 3 tall to 1 dwarf.

Answer: (d) only O

Explanation:
1. Group O has the genotype \(ii\) only, which is homozygous.
2. Group A (\(I^AI^A\) or \(I^Ai\)) and group B (\(I^BI^B\) or \(I^Bi\)) can be homozygous or heterozygous, and group AB (\(I^AI^B\)) is always heterozygous.

Teacher's Note:
1. AB is the only group that is always heterozygous.
2. A and B are codominant alleles, and i is recessive.

Answer: (c) a blood cholesterol lowering agent

Explanation:
1. Statins are produced by the yeast \(\textit{Monascus purpureus}\). They inhibit the enzyme that makes cholesterol, so they lower blood cholesterol.
2. Cyclosporin A is the immunosuppressive agent and streptokinase is the clot buster.

Teacher's Note:
1. Statins competitively inhibit HMG-CoA reductase.
2. Bt toxin from Bacillus thuringiensis is the bioinsecticide.

Answer: (c) 3

Explanation:
1. Each pollen tube carries two non-motile male gametes, so (a) and (c) are correct and (b) is false.
2. The pollen tube grows towards the ovule guided by chemical substances from the synergids, so it is chemotropic and (d) is correct. So three statements are correct.

Teacher's Note:
1. Angiosperm male gametes are carried passively in the pollen tube.
2. The filiform apparatus of the synergids guides the pollen tube.

Answer: (c) 50

Explanation:
1. Each microspore mother cell (pollen mother cell) divides by meiosis to give 4 microspores, which develop into 4 pollen grains.
2. Number of mother cells \(= \dfrac{200}{4} = 50\).

Teacher's Note:
1. Meiosis in a PMC produces a tetrad of four haploid microspores.
2. For a megaspore mother cell, the result is only one functional megaspore.

Answer: (a) 36, 24 and 12

Explanation:
1. The gametes are haploid, so \(n = 12\).
2. The primary endosperm cell is triploid (\(3n = 36\)), the embryo develops from the zygote and is diploid (\(2n = 24\)), and the synergids are haploid (\(n = 12\)).

Teacher's Note:
1. Primary endosperm nucleus = two polar nuclei plus one male gamete.
2. Synergids arise from the megaspore by mitosis, so they are haploid.

Answer: (b) 32

Explanation:
1. In each PCR cycle the amount of DNA doubles, so after \(n\) cycles there are \(2^n\) copies from one molecule.
2. After 5 cycles, \(2^5 = 32\) copies.

Teacher's Note:
1. PCR uses denaturation, annealing and extension in every cycle.
2. A thermostable Taq polymerase is used.

Answer: (d) protect its DNA from its own restriction enzyme

Explanation:
1. Bacteria make restriction endonucleases to cut the DNA of invading viruses. They protect their own DNA by adding methyl groups to it, which blocks the restriction enzyme from cutting it.

Teacher's Note:
1. The methylase and the restriction enzyme recognise the same sequence.
2. This is called a restriction-modification system.

Answer: (d) \(\textit{Pseudomonas putida}\)

Explanation:
1. Ananda Mohan Chakrabarty developed a strain of \(\textit{Pseudomonas putida}\) that can degrade hydrocarbons in crude oil.
2. \(\textit{Agrobacterium tumefaciens}\) is the vector for plant gene transfer.

Teacher's Note:
1. This was the first patented genetically modified organism.
2. Such bacteria are used in bioremediation.

Answer: (b) corn borer

Explanation:
1. The genes \(\textit{cryIAc}\) and \(\textit{cryIIAb}\) control cotton bollworms, and \(\textit{cryIAb}\) controls the corn borer.
2. Nematodes and flies are controlled by other cry genes.

Teacher's Note:
1. Bt toxin is produced as an inactive protoxin that becomes active in the alkaline gut of the insect.
2. The toxin creates pores in the midgut epithelial cells.

Answer: (c) B and D

Explanation:
1. (A) is wrong because Atlas 66 is a wheat variety with high protein content, not minerals.
2. (B) is correct since single cell protein is an alternative protein source. (C) is wrong because micropropagated plants are somaclones, genetically identical to the parent. (D) is correct.
3. So B and D are correct.

Teacher's Note:
1. Micropropagation is a form of cloning.
2. Biofortified crops are bred for higher protein, vitamins, minerals or healthier fats.

Answer: (b) could be permanent if the gene is introduced in the early embryonic stages

Explanation:
1. Gene therapy delivers a normal gene to replace a defective one. If it is introduced into cells in the early embryonic stage, it can be passed on and be a permanent cure.
2. It has been tried in humans, for example for ADA deficiency, and it does not involve introducing non-functional genes.

Teacher's Note:
1. In ADA deficiency, lymphocytes are corrected outside the body and returned, but they die, so the treatment is temporary.
2. Permanent correction needs the gene to enter the cells that give rise to all other cells.

Answer: (d) All of these.

Explanation:
1. Transgenic animals, mostly mice, are made so that the role of a gene in disease can be studied and new treatments can be tested on them.
2. Models exist for several diseases, including cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's disease.
3. So all the statements are correct.

Teacher's Note:
1. Transgenic animals are also used for making biological products and testing vaccines.
2. Safety testing of drugs is another important use.

Answer: (b) prolactin

Explanation:
1. Prolactin from the anterior pituitary stimulates milk synthesis after delivery.
2. Oxytocin causes the ejection of milk (and uterine contractions). Progesterone and oestrogen help in the growth of the mammary glands during pregnancy.

Teacher's Note:
1. Prolactin makes milk, and oxytocin releases it.
2. Colostrum is the first milk produced after delivery.

Answer: (a) condoms

Explanation:
1. Condoms are a barrier method, and they stop direct contact between the genital surfaces, so they protect against STDs and AIDS.
2. Copper T (IUD), Saheli (non-steroidal pill) and Norplant (implant) do not provide a barrier.

Teacher's Note:
1. Condoms are also the most widely used male contraceptive.
2. Nirodh is a popular brand in India.

Answer: (c) cryptorchidism

Explanation:
1. The testes normally descend into the scrotum before birth. If one or both fail to descend, the condition is cryptorchidism, and the higher temperature of the abdomen stops sperm formation.
2. Castration is the removal of the testes.

Teacher's Note:
1. The scrotum keeps the testes about 2 to 2.5 degrees Celsius below body temperature.
2. Paedogenesis is reproduction by a larval stage.

Answer: (b) inguinal canal

Explanation:
1. The testes descend from the abdomen into the scrotum during development through the inguinal canal. This canal remains as the communication between the scrotal sac and the abdominal cavity.

Teacher's Note:
1. A weak inguinal canal can lead to an inguinal hernia.
2. The vas deferens passes through this canal to reach the abdomen.