Biology Test - 6

Klinefelter syndrome (or XXY syndrome) is a chromosome disorder that affects males. The affected male has an additional X chromosome, which causes infertility and may cause the development of characteristics such as tall stature and breast development.

Hence option C is correct.

Grey crescent is a crescent-like and grey colored area developing on the surface of frog egg opposite to the point of sperm entry. It's materials function as the organizer. The grey crescent marks the future dorsal side of the embryo. The first cleavage bisects the grey crescent into two equal halves and this plane represents the future median plane of the embryo. During gastrulation phase of frog, the first cells to form the dorsal lip are endodermal cells. These cells later become the pharyngeal cells of the foregut. The next cells over the dorsal lip of the blastopore are called the chorda mesoderm cells. These cells will form the notochord, a transient mesodermal backbone that is essential for initiating the differentiation of nervous system.

Hence option D is correct

The lac operon (lactose operon) is an operon required for the transport and metabolism of lactose in Escherichia coli and many other bacteria. It contains genes involved in lactose metabolism. It is expressed only when lactose is present and glucose is absent.

Two regulators turn the operon "on" and "off" in response to lactose and glucose levels: the lac repressor and catabolite activator protein (CAP). Catabolite activator protein (CAP) acts as a glucose sensor. It activates transcription of the operon, but only when glucose levels are low. CAP senses glucose indirectly, through the "hunger signal" molecule cAMP.

So, the correct option is C.

Bacteria has 70S ribosome. The 30S sununit has 16S rRNA and 50S subunit has 23S and 5S rRNA. 23S rRNA has peptidyl transferase activity and catalyze the synthesis of peptide bond formation between amino acids in bacteria. This rRNA also serve as structural component for large subunit of bacterial ribosome.

Therefore, the correct answer is option A.

Corona radiata is the layer placed adjacent to the zona pellucida. It provides proteins to the developing ovum. It is made up of tall pillar-like cells.

Zona pellucida is a glycoprotein layer. It is paced outer to the plasma membrane of the oocytes. It binds to spermatozoa, and initiate the acrosome reaction.

The vitelline membrane surrounds the outer surface of the plasma membrane and it helps in the binding of spermatozoa.

So, the correct answer is option A.

A. Triticum turgidum is known as Emmer wheat and is tetraploid.

B. Triticum durum is known as Pasta wheat and is tetraploid.

C. Triticum monococcum is known as Einkorn wheat and is diploid.

D. Triticum aestivum is known the bread wheat and is hexaploidy.

Hence, the hexaploidy wheat used to make bread. So, the correct answer is 'Triticum aestivum'.

Hence option D is correct

Lac operon is made up of one regulator, one operator and three structural genes. The three structural genes are LacZ, LacY and LacA. LacZ encodes β-galactosidase (LacZ), an intracellular enzyme that cleaves the disaccharide lactose into glucose and galactose. LacY encodes beta permease which pumps the lactose inside the cell. Lac A encodes beta transacetylase which removes toxic substances from the cell.

The regulator gene produces m-RNA which translates into the repressor. The repressor attaches to the operator and blocks the expression of the structural gene in absence of inducer. In presence of inducer, the repressor attaches to the inducer and operator is not blocked so it allows the expression of the structural gene. Operator genes are a region of DNA sequence which attaches to the repressor molecule and stops the expression of the structural gene.

So, the correct answer is option C.

During initial days of lactation, the yellowish fluid colostrum secreted by the mother has abundant antibodies Ig A to protect the newborn against diseases. Colostrum has greater nutrient value than mature milk. It provides the initial immune response.

So, the correct answer is option A.

Heterosis or hybrid vigour means the increased vigour (size, strength etc.) of a hybrid than its parents. As it is a hybrid, it is always superior than either of its parents. In plants, heterosis is expressed in the form of height, viability, greater yield of fruits and seeds, increased resistance to environmental factors, resistance to diseases, pests and better seed germination. Heterosis has been commercially exploited in many crops like maize by crossing of two inbred parental lines. The vigour is lost after few generations.

Hence option C is correct.

All vertebrate eggs are strongly polar structures. The two opposite poles are differentiated as animal pole and vegetal pole. The imaginary axis passing through these two poles is called polar axis or animal-vegetal axis. It is the main axis of an egg. Polarity is usually expressed as a gradient in the ratio of cytoplasm and yolk from animal to vegetal pole. Polarity is responsible for the differentiation of egg as a bipolar structure.

So, the correct answer is option B.

Pseudocoelom is the fluid-filled main body cavity, that separates the digestive tract and the outer body wall, which may be unlined or partially lined with tissues derived from mesoderm. The pseudocoelom is a persistent blastocoel or fluid-filled cavity of the blastula stage of embryo.

Thus, the correct answer is option (A).

The process of translocation is a kind of rearrangement in which block of genes from one chromosome are transferred to other non-homologous chromosome. Breaks in chromosomes are followed by union in ways different from the normal one.

So, the correct answer is 'A part of one chromosome is exchanged between non-homologous counterpart'.

Hence option B is correct.

The method of transfection or transduction is used when there is the transfer of the gene into the cell with the help of virus or phage. The bacteriophage is the virus which attacks the bacterial cells. These viruses transfer the genetic material from one bacterium to the other during infection.

Thus, the correct answer is option D.

Histones are the special type of low molecular weight, positively charged proteins which are rich in basic amino acids like lysine and arginine. There are five types of histone proteins, HI, H2A, H2B, H3, and H4. Four of them (H2A, H2B, H3, and H4) occur in a pair to produce histone octamer called the core of nucleosome. The positively charged end of these histones proteins are towards outside, to attract and hold firmly the negatively charged strand of DNA. About 166 bp of DNA is wrapped over the nucleosome body.

The DNA connecting the two adjacent nucleosomes is called linker DNA. It bears H1 histone protein which connects one core particle with the other. This completes the structure a negatively charged DNA wrapped around the positively charged histone octamer called nucleosome. The nucleosome and linker DNA are together referred to as chromatosome. The nucleosomal organisation has approximately 10 nm thickness which gets condensed and coil to form a solenoid of 30 nm diameter. The coiling undergoes further coiling to produce a chromatin fibre of 30-80 nm, then a chromatid of 700 nm.

Hence the histones facilitate the coiling of DNA molecule to form Chromatin fibre. So, the correct answer is 'Chromatin'.

Hence option B is correct.

The histone proteins are positively charged molecules. The DNA is negatively charged due to the presence of the phosphate backbone. The interaction between the DNA molecules and the histone proteins allows forming the structure called the nucleoid. This nucleoid is packed and condensed to form the structure of DNA which can be easily packaged in the nucleus.

There are certain regions on the chromosomes which are known as satellites. These regions are denoted due to constrictions other than the centromere. This is the regions which are not stained and are present at a fixed location. There are many repeated sequences in this region.

Thus, the correct answer is option D.