AIDS

• The term AIDS stands for Acquired Immuno Deficiency Syndrome.
• The disease is acquired during life time.
• AIDS is caused by human immune deficiency virus (HIV).
• HIV is a retrovirus having RNA as the genetic material.

Mode of transmission-

• Sexual contact with infected persons.
• Bytransfusion of contaminated blood and blood products.
• By sharinginfected needles as in the case of intravenous drug abusers.
• From infected mother to her child through placenta.

Life cycle of HIV

• After getting into the body the virus enters into macrophages or T-helper cells.
• The viral RNA genome replicated to form viral DNA with the enzyme called reverse transcriptase.
• The viral DNA gets incorporated into the host cell’s DNA and directs the infected cells to produce virus particles and the macrophages continue to produce virus.
• Viruses released from macrophages attack T-helper cells and cause a progressive reduction in the number of T-helper cells and due to which the person starts suffering from infections with several other microorganisms.

Diagnosed by ELISA (enzyme linked immune-sorbent assay).

Treated with anti-retroviral drugs but that is only partially effective.

Prevention of AIDS-

• To follow safe blood transfusion.
• To use disposable needles.
• To distribute free condoms.
• To prevent drug abuse.

External genitalia

• ****** is the female external genitalia.
• ****** includes mons pubis, ***** majora (***** majus), ***** minora (***** minus), hymen and ********.
• Mons pubis is a cushion of fatty tissue covered by skin and pubic hair.
• The ***** majora are folds of tissue extend down from the mons pubis and surround the vaginal opening.
• Under the ***** majore, there are paired tissue folded to form ***** monora.
• Hymen is membrane covering the opening of the ******.
• A tiny finger-like structure which lies at the upperjunction of the two ***** minora above the urethral opening is called ********.

1 : the center especially of an anatomical part. 2 : the body of a vertebra ventral to the neural arch. 3. the part of a vertebra supporting the disks in a spinal column .

Gene expression in prokaryotes

Gene expression refers to the molecular mechanism by which a gene expresses a phenotype by synthesizing a protein or an enzyme. Which determines the character. The gene contains the blue print or the information for the protein or an enzyme.

The category includes mechanism involved in the rapid turn-on and turn-off gene expression in response to environmental changes. Regulatory mechanism of this type are very important in microorganisms, because of the frequent exposure of these organisms to sudden changes in environment.

Gene concept can be studied by operon model. Operon are segment of genetic material which function as regulated unit that can be switched on and switched off, which was given by French scientists. Jacob and Monod (1961) working at Pasteur institute. They were studying lactose utilization in mutants of E.coli. An operon consists of one to several structural genes (three in lac operon and five in tryptophan operon of Escherichia coli, nine in histidine operon of Salmonella typhimurium), an operator gene a promoter gene a regulator gene, a repressor and inducer or corepressor.

Genes are contained in chromosomes, which are in the cell nucleus. A chromosome contains hundreds to thousands of genes. Every normal human cell contains 23 pairs of chromosomes, for a total of 46 chromosomes. A trait is any gene-determined characteristic and is often determined by more than one gene. The child can end up with two copies of chromosome 22, one copy, a copy attached to chromosome nine, or no copies at all. So each child has an equal chance for trisomy, a missing chromosome (called monosomy), the same balanced translocation, or the usual assortment of chromosomes.

SARS is short for Severe acute respiratory syndrome. It is a viral respiratory disease in humans which is caused by the SARS coronavirus (an RNA virus).

Initial symptoms are flu-like and may include: fever, lethargy symptoms, cough, sore throat and other nonspecific symptoms. Shortness of breath may occur later.

In 1929 the British biologist John Burdon Sanderson Haldane published a hypothesis on the origin of life on earth, which was one of the most emblematic of the interwar period. It was a scenario describing the progressive evolution of matter on the primitive earth and the emergence of life. The Oparin-Haldane hypothesis suggests that life arose gradually from inorganic molecules, with “building blocks” like amino acids forming first and then combining to make complex polymers. ... Some scientists support the RNA world hypothesis, which suggests that the first life was self-replicating RNA.

Crossing over:

Crossing over may be defined as an exchange of genetic material between non- sister chromatids of homologous chromosomes resulting in a new combination of genes.

The crossing over takes place during the early stage of prophase first of meiosis ce;; division.

Mechanism of crossing over:

The process of crossing over involves the following stages:

1.Synapsis

2.Duplication of chromosomes

3.Crossing over

4.chiasmata formation

5.Terminalisation

1.Synapsis:During zygotene substage of prophase I, the maternal and paternal homologous chromosomes come close to each other and start pairing along their length. The pairing of homologous chromosomes is called synapsis. They paired homologous chromosomes are called bivalents. It is mechanical basis of crossing over.

2.Duplication of chromosomes: The synapsis is followed by duplication of chromosomes. During pachytene substage of prophase I , the chromotids of each homologous chromosome splits lengthwise and forms two identical sister chromatids.Thus each bivalent contains four chromatids so it is known as tetrad.

3.Crossing over: The non-sister chromatids of homologous pair twist over each other at one or more points. The chromatid segments break at the corresponding points and the segment of one side fuses with the segment of the opposite side due to the action of enzyme. Thus the crossing over includes breaking of chromatid segments, their transposition and fusion.

4.Chiasmata Formation: Chiasmata are the points of attachment between two homologous chromosomes, where the crossing over occurs. The number of chiasmata depends on the length of the chromosomes;  greater the length greater is the number.The crossing over may take place at one or several points in one tetrad and may result in the formation of one or more chiasma.

5.Terminalisation: After the process of crossing over, the non- sister chromatids start to repel each other due to lack of attraction force between them. The repulsion of chromatids starts from the centromere towards the chiasma and the chiasma itself moves in a zipper fashion towards the end of the tetrad. The movement of chiasma is known as terminalization. Due to terminalisation the hlomologous are separated completely.

Autosomal recessive is one of several ways that a trait, disorder, or disease can be passed down through families. An autosomal recessive disorder means two copies of an abnormal gene must be present in order for the disease or trait to develop.

The nucleus of each microspore mother cell undergoes meiosis or reduction division and gives rise to four haploid nuclei. This process is called microsporogenesis. The four nuclei are arranged tetrahedrally and soon get enclosed with cell walls. These are now called microspores or pollen grains. These microspores fiurther divide once by mitosis to form two-celled microspore. differentiates into pollen grain. Each microspore  The pollen grains soon dry up and become powdery while the tapetum gets absorbed. The partition walls between the sporangia get destroyed and the microspores are liberated by the dehiscence of the anther.

The nucleus of each microspore mother cell undergoes meiosis or reduction division and gives rise to four haploid nuclei. This process is called microsporogenesis. The four nuclei are arranged tetrahedrally and soon get enclosed with cell walls. These are now called microspores or pollen grains. These microspores fiurther divide once by mitosis to form two-celled microspore. differentiates into pollen grain. Each microspore  The pollen grains soon dry up and become powdery while the tapetum gets absorbed. The partition walls between the sporangia get destroyed and the microspores are liberated by the dehiscence of the anthe

Significance of cervix in female reproduction :

Cervix : This is the structure which is present at the lower region of the uterus . The cervix opens to allow the entry of sperm and during the child birth. 

Lac operon consists of regulator gene, promoter gene, operational gene and structural gene. The E. coli bacterium carries numerous genes and these genes turn on and off as per requirement. When these genes are turned on, they undergo enzymes which metabolise the new substrate. This phenomenon is known as induction and small molecules eliciting this induction is referred to as inducers. 

In this lac operon, the presence of lactose acts as an inducer. The lac operon contains a promoter, an operator and three closely related structural genes, z, y, a coding for enzymes β-galactosidase, β-galactoside permease and β- galactoside transacetylase respectively. β-galactoside permease pumps lactose into the cells whereas β-galactosidase catalyses the conversion of lactose into glucose and galactose. These genes are not expressed in the absence of lactose. 

The promoter (P) for the operon is the site at which RNA polymerase binds to initiate transcription of the structural genes. The operator (O) is the site at which the protein repressor – the product of regulator gene binds. In the presence of a regulator protein, the RNA polymerase is prevented from attaching to the promoter. A regulator gene is a DNA segment independent of an operon and it synthesizes a repressor protein. This protein combines with an operator and makes it inactive. This prevents RNA polymerase from binding to the adjoining promoter (P) and from initiating transcription of the structural gene. Therefore, RNA polymerase is required to negotiate the operator before transcription can occur. 

The repressor binds to the operator in the absence of a metabolite (effector molecule – lactose). When an inducer or effector molecule-lactose is added to the system, it binds to the repressor to form a complex which is unable to bind the operator. The RNA polymerase enzyme now becomes free to bind with a promoter (P) and so the operator is switched on. This initiates the transcription of structural genes, producing the three polypeptides. These enzymes bring about the metabolism of lactose into glucose and galactose.

The lac operon (Inducible operon) Operon :

The concept of operon was first proposed in 1961, by Jacob and Monod.

Components of an operon :

(i) Structural genes : - The fragment of DNA which transcribe mRNA for polypeptide synthesis.

(ii) Promoter : - The sequence of DNA where RNA polymerase binds and initiates transcription.

(iii) Operator : - The sequence of DNA adjacent to promoter is called OPERATER.

(iv) Regulator gene : - It is the gene that codes for repressor protein which binds to operator due to which operon is switched ‘‘off’’

(v) Inducer : - Lactose is inducer which helps in switching ‘‘on’’ of operon. Lac operon consists of there structural genes (z, y, a), operator (o), promoter (p), regulatory gene

• Alien DNA can be introduced into the host cell by the biolistics method.
• The Plant cells are bombarded with high velocity of gold or tungsten coated with DNA by this Biolistics or gene gun method.

A. Microinjection is a technique in which DNA is directly injected into the host cells with the help of microinjection.

B. Electroporation is a technique in which pores are created in the cell membrane and thus, permeability is increased. As a result, foreign DNA can easily enter the cells.

C. Gene gun is a method to introduce alien DNA into host cells through microprojectile particles. The DNA coated gold or tungsten particles are bombarded with the host cells and alien DNA enters the cells.

Small animals have larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; therefore they have to expend much energy to generate body heat through metabolism. This is the reason why polar regions are not a suitable habitat for tiny humming birds.

Small animals have larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; therefore they have to expend much energy to generate body heat through metabolism. This is the reason why polar regions are not a suitable habitat for tiny humming birds.

one that precedes and indicates the approach of another.

White Blood Cells ( WBCs ) , or leukocytes ( from the Greek word leuko - meaning “ white ”  ) , are cells of the immune system involved in defending the body against both infectious disease and foreign materials .