Sexual Reproduction in human beings involves :
Gametogenesis : formation of sperm in male and ovum in female.
Insemination : transfer of sperm into female genital tract.
Fertilization : fusion of sperm and ovum to form zygote.
Implantation : development of blastocyst and its attachment to uterine wall.
Gestation : embryonic development.
Parturition : birth of the baby.
MALE REPRODUCTIVE SYSTEM :It consists of :
A pair of testis
Male accessory gland
Male accessory duct.
Testis -A pair of oval testis 4-5 cm. long 2-3cm wide are present in a pouch like structure called scrotum. Each testis has 250 compartment called testicular lobules. Seminiferous tubules are highly coiled tubes present in lobules which contain two types of cells, male germ cell (spermatogania) and sertoli cellsInterstitial space around seminiferous tubules contains interstitial cell or Leydig cells.
Spermatogenic cell : develop in to sperm
Sertoli cells : provide nourishment to developing sperm.
Leyding cell : secretion of androgen hormone.
Male Accessory Ducts:These include rete testis, vasa efferentia, epididymis and vas deferens. These tubules form a very long & complicated system for storage and transport mature sperms.A pair of vas deferens ascends to the abdomen and loop over urinary bladder.
Male Accessory Gland :Includes A pair of seminal vesicles. A prostate gland A pair of bulbo-urethral gland or Cowper’s gland: also help in lubrication of penis.
External genitalia: It consists of penis though which urethra opens out as urethral meatus. It has a swollen tip called glans penis covered by membrane called foreskin.
FEMALE REPRODUCTIVE SYSTEM :
a) A pair of ovaries. b) A pair of oviduct or fallopian tubesc) Uterusd) Cervix e) Vaginaf) External genitaliag) A pair of mammary gland.
Ovaries: These are primary female sex organ about 2-4cm long almond shaped, located on each side of abdomen to pelvic wall and uterus. Their function is to produce ovum and ovarian hormones i.e. estrogen and progesterone.
Oviducts or fallopian tubes : It is about 10-12cm long, extending from funnel shaped infundibulum near ovaries to uterus. Infundibulum leads to wider ampulla which is connect through isthmus to uterus on both sides.
Uterus : It is also called womb. It is inverted pear shape open into vagina through cervical canal. Uterus wall consist of three layers – perimetrium, myometrium and endometrium. Endometrium undergoes cyclic changes during menstrual cycle while myometrium has smooth muscles which help in parturition.
External genitalia : In consists of mons pubis, labia majora, labia minora, hymen and clitoris.
Mammary gland : A pair of Mammary glands produce milk during lactation. Glandular tissue of mammary gland is divided into 15-20 mammary lobes, which contain alveoli. Through lactiferous duct, milk is suck out of mammary gland.
Gametogenesis: Gametogenesis involves the formation of haploid gametes in gonads. In male, it is spermatogenesis and in female, it is oogenesis.
1st Meiotic division
2nd Meiotic division
1st Meiotic division
2nd Meiotic division
Menstrual cycle :It involves of cyclic changes in the ovaries which culminate into the periodic vaginal bleeding called menstruation. On an average, it is completed in 28 days. It consists of four phases:-
a) Proliferative phase
b) Ovulatory phase
c) Luteal phase
d) Menstrual phase
Proliferative Phase : It involves growth and proliferation of uterine endometrium, fallopian tubes and vagina while ovulation occurs.
Ovulatory phase: It is characterized by rupture of Graafian follicle and release of ovum.
Luteal Phase: Characterized by change of empty Graafian follicle into a corpus luteum which secretes progesterone.
Menstruation Phase : It is followed by Luteal phase, if the ovum remains unfertilized. If fertilization occurs, it is followed by implantation and normal growth of foetus.
Fertilization and Implantation :
It includes four steps
a) Approach of sperm to ovum
b) Penetration of sperm into ovary
c) Activation of ovum
d) Fusion of gametic nuclei
Semen is released in the vagina during copulation. Fertilization is caused by the fusion of sperm and ova in ampullary – isthmic junction. Sperm causes changes in zona pellucida membrane to prevent polyspermy.
Main significance of fertilization is to restore dipliody.
Implantation leads to the beginning of pregnancy. Cleavage is the process in which the zygote undergoes rapid mitotic divisions to form blastula. The cleavage initially forms a solid ball like morula. Morula changes into blastocyst.Blastocyst enters the uterus about 72 hour after fertilization and gets implanted to endometrium of the uterus on to 7th day.
Blastocyst consists of inner cells and outer trophoblasts. Trophoblasts help its attachment with the endometrium while inner cells differentiate into ectoderm, mesoderm and endoderm. All major organs get formed till the embryo is 12 weeks from these three germ layers.
Pregnancy and Parturition :
Placenta: The Human placenta is formed by chorionic villi of trophoblast surrounded by uterine tissue and material blood for the developing embryo.
Placenta – (its significance)
Helps in exchange of oxygen and CO2 between the mother and the foetus.
Helps in the elimination of nitrogenous wastes of the foetus.
Acts as an endocrine gland and secrets a hormone such as HCG (Human Chorionic Gonadotropin), Human placental lactogen (hPL), estrogen and progesterone.
Parturition and Lactation:
Parturition: The process of vigorous contraction of myometrium to expel the foetus is called parturition.
Lactation: Colostrum is the first milk that is secreted from the mother’s mammary glands just after the child birth. It is rich in calories and proteins and also contains antibodies to provide passive immunity to the new born infant. Synthesis of milk is stimulated by the prolactin. Its release is stimulated by oxytocin.
REPRODUCTIVE HEALTH:- It refers to as a total well being in physical, emotional, behavioral and social aspects of reproduction.
AMNIOCENTHESIS:- The process of detection of sex of an embryo is known as amniocentesis. It is carried out by testing of amniotic fluid of the developing foetus . It is a process which is misused to which the female child ratio becomes decreases.
CDRI- Central Drug Research Institute.
Population explosion:- Increasing no. of individual per unit area is known as population explosion. It is due to decreased in (MMR) & (IMR).
*MMR-maternal mortality rate.
*IMR-infant mortality rate.
Birth control:- The regulation of conception by preventive methods or devices to limit the number of offspring is called birth control.
It can be carried out by three methods:-
1) Natural method:- avoiding foetus during the days from 10-17 days after menstrual cycle in which the changes of ovum formation is high. The automatic seizing of menstruation during the lactation makes a condition known as lactational amenorrhea, in which no ovum is formed(less the chance of fertilization). (a) Safe period:- a week before and a week after menses is considered as the safe period for sexual intercourse. The ideas based on the following facts::
—ovulation occurs on about 14th day(may be 13th to 16th day) of menstruation.
—ovum survives for about 1-2 days.
—sperms remain alive for about 3 days.
This method may reduce the chances of pregnancy by about 80%. However, a great care is needed in its use.
(b) Coitus Interruptus:- this is the oldest method to birth control. It involves withdrawal of the penis from the vagina by the male before ejaculation so that the semen is not deposited in the vagina and there is no fertilization.
(c) Lactational Amenorrhea:- it is based on the fact that ovulation and therefore the menstrual cycle do not occur during the period of intense lactation following child birth(parturition). This method is considered effective only upto a maximum period of six months following parturition and has no side effects.
2) Barrier method:- by avoiding the contacts sperm and ovum by using physical barriers like cervical caps and intrauterine Device. Also by taking various female hormones in the forms of contraceptive peels. IUDs- It is generally made up of coppers and which is commonly known as copper-T which is allowed to present inside the uterus which releases the copper ion which sterilized the active sperm and also disturbs the embryo just after sterilization.
3) Surgical method:- this is also known as sterilization. The mature sperm and ovum are not allowed to meet with each other. It advised for the male/female partner as a terminal method to prevent any more pregnancies. Surgical intervention blocks gamete transport and prevents conception.
Vasectomyà sterilization procedure in the male.
Tubectomyà sterilization procedure in the female.
MEDICAL TERMINATION OF PREGNANCY
Intentional or voluntary of pregnancy before the foetus becomes viable is called medical termination of pregnancyor induced abortion. It is a process of destroying the developing embryo due to certain imbalance in health of female. During this process the developing embryo is checked by the application of chemicals or physically disturb by the help of needle after this destroyed cells of embryo sucked out from the uterus. It is safe upto 12 weeks of pregnancy.It is one of the most widely used methods of fertility control. Nearly 45 to 50 million induced abortions are performed in a year in all over the world, which account to 1/5th of the total number of conceived pregnancies in a year.
— MTP is done to get rid of unwanted pregnancies due to:
(a). Casual unprotected intercourse. (b). Rapes.
(c). Failure of contraceptive used during coitus.
SEXUALLY TRANSMITTED DISEASES (STDs)These are the disease which is generated due to disturbances of hormonal secretion or also by various physical agents mainly by bacteria and virus, commonly known as STDs or VD or RTI.Examples:- HIV leading to AIDS, gonorrhea, syphilis, genital herpes, chlamydiasis, genital warts, trichomonasis, hepatitis-B are few common STDs.
Though all persons are vulnerable to these infections, their incidence is very high among adolescents in the age group of 15-24 years.
SOME COMMON STDs AND THEIR CAUSATIVE AGENTS.
SOME MEASURES TO PREVENTFROM CONTRACTING STDs
WHO à World health organization.
Principles of Inheritance & Variations.
Principles of inheritance and variation.
Law of Dominance:
Law of Segregation:The two allelomorhic characters of an individual do not get mixed up by they segregate during gamete formation. Each gamete receives only one character of the two allelomorphs and a pair condition is restored by random fusion of gametes during fertilization.
Test Cross: It is a cross between F1 hybrid and the recessive parent.To confirm the purity of F1 hybrid, whether it is homozygous, a test cross is done.
a) If the test cross yields off springs of 50% dominant and 50% recessive character, then the F1 hybrid is heterozygous. It shows (1:1) test ratio for monohybrid cross and (1:1:1:1) for dihybrid cross.
b) If the test cross yields all the dominant character, the F1 hybrid is homozygous.
Which a inter cross is done between two genetically different parents, a hybrid is produced which may be homozygous are heterozygous. To determine the purity of parents & to test genotype of F1 Hybrid, a cross is made between F1 hybrid and on of the parent. Such a cross is known as back cross.
Exception of Principle of Dominance:
The phenomenon of incomplete dominance occurs in four ‘O’ Clock plant (Mirabilis jalapa) & Snapdragon(Antirrhinum majus) and Andalusian fowls.
Co-Dominance: when both alleles of a pair are fully expressed in a heterozygote, the genes and trait are said to be co-dominant.
AB Blood Group.
Sickle Cell AnaemiaC) Multiple Alleles: More than two alternate forms of a gene present on the same locus are called multiple alleles.
Example; Inheritance of blood group.
Principle of Law of Independent Assortment:
When two pairs of independent alleles are brought together, they show independent dominant effects. During the formation of gametes the genes of different characteristics are independent of one another.
Chromosomal theory of Inheritance:
Walter Sutton and Theodor Boveri proposed the Chromosome theory of Inheritance. Main features of chromosome theory of inheritance:
Nucleus contains chromosomes. Therefore, chromosome must carry the heredity traits.
Gametes contain only one chromosome of a type and only one of two alleles of trait.
The pained condition of both chromosomes as well as Mandelian factors is restored during fertilization.
Each chromosome contains numerous genes & the positions assigned to each gene is called locus. These genes help the organism to develop from the Zygote.
Each chromosome retains its individuality, uniqueness & continuity throughout the life of an organism and from generations to generation. They never get last or mixed up but behave as units.
Linkage & Recombination:
A chromosome contains large number of genes in a linear order and these genes belonging to a particular chromosome tend to be inherited together. This tendency of genes to remain together during the process of inheritance is called as linkage. Morgan (1990) proved and defined linkage on the basis of his breading experiments in fruitfy (Drosophila melanogaster).
Morgan etal observed that when two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combination were much higher than the non parental types.
Morgan attributed this to the physical association of the two genes which he referred as linkage and the term recombination to the non-parental combinations different from the parental types.
Linkage maps or Chromosomes Maps:
A linkage or genetic chromosome map in a linear respiration of the sequence & relative distances of the various genes present in a chromosome. The first chromosome maps were prepared by Sturtevant in 1911 from two chromosome of Drosophila.
Determination of Sex:
Chromosome theory of sex put forwarded by Wilson and Stevens (1950) and named X and Y bodies as sex chromosomes, X and Y.
It is of the following types:
14. Genetic Variations:
Mutation – it is the sudden, discontinuous and heritable change which alters the phenotype of an individual. The term “mutation” was coined by Hugo de Vices (1901).
Types of mutation due to change in structure of chromosome.
Chromosomal mutation may alter the structure of chromosomes.
Deletion (Deficiency) – A segment of chromosome separate and lost.
Duplication – It is the phenomenon of having an extra chromosome segment attached to a normal segment.
Inversion – A segment of chromosome separates and rejoins at in an inverted position. It results in the change in sequence of nitrogenous base or genes in chromosome.
Point mutation is the abrupt change in gene structure due to change in a single base pair of DNA due inversion and substitution, without changing the reading of subsequent bases.
Example: Sickle Cell Anaemia.
Frame shift mutation is the elimination or addition of one or two base pairs or a segment of DNA in a gene. It leads to chain of triplet codon on m-DNA that is responsible for polypeptide chain. It results in lateral sifting of entire reading frames from the site of mutation.
Thalassemia – an inherited blood disorder is an example of frame shift mutation.
15. Pedigree Analysis:
It is a chart to represent the data collected from a family over a number of generations for a certain genetic trait by using international conventional symbol. It reveals the ancestral history of an individual and its possible genotype for a trait.
16. Human Genetic Disorders:
a) Mendelian Disorders:
I) Sickle Cell Anaemia: Sickle cell Anaemia is an autosomal hereditary disorder in which
The erythrocytes form biconcave disc to elongated sickle like structure under low oxygen deficiency as during strenuous exercise and at high altitudes.
The disorder or disease is caused by the formation of abnormal haemoglobin
called Haemoglobin-S which differs from normal Haemoglobin-A in only one Amino Acid
– 6th amino acid of B-Chain, glutamic acid is replaced by valine.
II) Phenylketonuria: it is an inborn error of metabolism which is inherited as autosomal recessive trait. The affected individual do not produced phenylalanine hydrolase which converts phenylalanine to tyrosine. So, in the absence of this enzyme, phenylalanine accumulates in the blood & produces toxic effect on CNS resulting irreversible brain damage, severe mental & physical retardation.
III Haemophilia: It is a sex linked disorder and it is also known as bleeder’s disease as the patient will continue to bleed even from a minor cut since he or she does not possess the natural phenomenon of blood clotting due to absence of anti haemophilic globulin or factor VIII and plasma thromboplastin factor IX essential for it.
b) Chromosomal Disorders:
Genetics: The study of Heredity and variations.
posted Dec 23, 2010 9:12 PM by jaleelkabdul jaleel [ updated Dec 24, 2010 4:20 AM ]
posted Dec 19, 2010 6:52 PM by jaleelkabdul jaleel [ updated 13 minutes ago ]
1. Deoxyribonucleic Acid (DNA):
# DNA is a long polymer of deoxyribonucleotides.
# the length of DNA is defined as the number of nucleotides present in it.
2. Structure of DNA:
* DNA is formed of number of nucleotides units.
* Each nucleotide has a nitrogenous base, a pentose sugar and inorganic phosphate.
* Nitrogen basis occur in DNA belonging to tw0o groups, purine and pyrimidine.
4. DNA as Genetic Model: (Griffith’s Experiment).
* It is the change in the genetic constitution of an organism by picking up genes present in the remains of its dead relatives.
* Transformation was first studied by S.F Griffith in1928 while studying on bacterium Streptococcus pneumoniaecalled pneumococcus.
* The bacteria has two strains – the smooth form(s) secretes a polysaccharide capsule which gives the colonies a smooth appearance and virulent. Another form is non-capsulated which gives the colonies a rough appearance and is not virulent (R)
*Griffith tested the virulence of the two strains by injecting the live R-type and live S-type separately into mice, he found that R-type bacteria were non-pathogenic while the S-type caused the death in the mice.
*Heat killed S-type bacteria into mice and they survived equally well
* In the last, he injected a mixture of heat killed “S” & live “R” simultaneously, the mice died with the symptoms of pneumonia. Living type S bacteria were recovered from their bodies.
5. Hershey and Chase experiment.
6. Mode of DNA Replication
DNA replication occurs during S-phase of cell cycle.
Mechanism of DNA replication is as follows:
* The process of copying genetic information from one strand of the DNA into RNA is called transcription.
8. Genetic Code:
• AUG has dual functions. It codes for Methionine (met), and it also act as initiating codon.
9. Protein Synthesis:
Mechanism of Protein synthesis in E.coli is given below:
• Polypeptide chain termination
• Arrangement of amino acids in specific sequence & formation of polypeptide chain according to the information present in m-RNA is called translation.
• Site of translation is ribosomes.
• Translation is a complex process which involves the participation of ribosomes, m-RNA, t-RNA& amino acids
Attachment of mRNA to ribosomes
ACTIVATION OF AMINOACIDS
• They are activated by specific aminoacyl t-RNA Synthetase enzymes,ATP is also required
• These enzymes possess two binding sites one for amino acid and the other for its t-RNA.
• Initiation of polypeptide chain
• It requires amino acyl t- RNA complex ,m-RNA with initiation codon,30 s and 50 s subunits of ribosomes,GTP& initiation factors.
• With the help of anticodon UAC, t-RNA carries FORMYL METHIONINE and attaches to AUG codon of m- RNA and forms initiation complex .
POLYPEPTIDE CHAIN ELONGATIONFormyl methionine moves from decoding site. A second amino acid is brought to A site by another aminoacyl t-RNA.A peptide bond is formed between the amino acids
Water is formed in this reaction .The movement of dipeptide from A site to P site is called Translocation.
POLYPEPTIDE CHAIN TERMINATION
• Terminator or non sense codons (UAA, UAG, &UGA) present on the m-RNA strand signal the termination of polypeptide chain.
10. The Lac-Operon:
* Inducer regulator switching on of the operon. The inducer of Lac-operon of Escherichia coli is lactose (actually allolactose).
Human Genome Project (HGP)
Goals of HGP
(i) Identify all the approximately 20,000-25.000 genes in human DNA;
(ii) Determine the sequences of the 3 billion chemical base pairs that make up human DNA;
(iii) Store this information in databases;
(iv) Improve tools for data analysis;
(v) Transfer related technologies to other sectors. such as industries;
(vi) Address the ethical, Legal, and social issues (ELSI) that may arise from the project.
Salient Features of Human Genome Project
- Codon: Sequence of three nitrogenous bases on mRNA, that code for a particular amino acid.
- Anticodon: Sequence of three nitrogenous bases on tRNA that
- is complementary to the codon for the particular amino acid.
- Bacteriophage: Viruses which infect bacteria.
- Operon: A transcriptionally regulated system consisting of structural gene, operator gene, promoter gene and regulator gene.
- Nucleotide: A complex biomolecule formed by the condensation of pentose sugar, base and one to three phosphoric acids.
- Polymer: A large biomolecule formed by the linking small units the monomers.
- Inducer: A chemical substance which regulate switching on and off the operator gene besides also act as substrate.
- Splicing: Process of removal of introns and joining of exons in HnRNA.
- Template: A strand which acts as model for the synthesis of a new strand.
- Nucleosome: A repeating unit of chromatin structure formed by
- mistune octamer and wrapped around DNA.
- Central Dogma: Unidirectional flow of genetic information from
- DNA — RNA——-Proteins.
- Promotor: A site, at which RNA polymerase is held.
- Coding Strand: Strand of DNA which does not code for anything.
- Translation: Process of polymerization of amino acids to form a peptide under the direction of base sequences in m-RNA.
- Introns: Non-coding segments of eukaryotic structural gene.
- Exons: Coding segments of eukaryotic structural gene.
- Euchromatin: Light stained loosely packed transcriptionally active chromatin.
- Heterochromatin: Dark stained compactly packed, inactive.
- Semi conservative: Type of replication in which DNA molecule has one parental and one newly synthesized strand.
- Genetic Code: A triplet base sequence regulating the sequence of amino acids in a polypeptide