Scientific End of Men..?Scientific End of Men..?

ByBy

Prof.S.Mohana,Prof.S.Mohana,

Tamil Nadu Science Forum.Tamil Nadu Science Forum.

Cell & chromosomesCell & chromosomes There are 46 chromosomes in There are 46 chromosomes in

the nucleus of our the nucleus of our body cellsbody cells.. Of these, 23 from our mother’s Of these, 23 from our mother’s

egg and 23 fromegg and 23 from father’s spermfather’s sperm When the egg and the sperm When the egg and the sperm

join together at time of join together at time of conception, they form the first conception, they form the first cell of the babycell of the baby

The baby’s body cells now The baby’s body cells now have 46 chromosomes, made have 46 chromosomes, made up of 23 pairs, just like the up of 23 pairs, just like the parents parents

Cells Cells The largest and smallest cells in the human The largest and smallest cells in the human

body are the gametes, or the sex cells. body are the gametes, or the sex cells. The female sex cell, the oocyte, is about The female sex cell, the oocyte, is about

35 microns in diameter, which puts it just 35 microns in diameter, which puts it just on the edge of being visible if you have real on the edge of being visible if you have real good eyes. good eyes.

The male sex cell, spermatozoan, cell is only The male sex cell, spermatozoan, cell is only about 3 microns in diameter, and therefore about 3 microns in diameter, and therefore is the smallest cell of the human body. is the smallest cell of the human body. 

Cell, chromosome & geneCell, chromosome & gene

Number of Human CellsNumber of Human Cells

  the average adult human body is made up of the average adult human body is made up of "50 million million" (50 trillion) cells, "50 million million" (50 trillion) cells,

There are approximately 30 trillion Red Blood Cells, 2 trillion Platelets, and 500 million White Blood Cells in your Circulatory System. In Lymph system, another trillion lymphocytes and immune related cells.a total of about 38-40 trillion cells. Naturally, most of the MASS in the body is comprised by the 4 trillion cells that make up your solid tissues, especially your muscle and skeletal cells.

Chromosomes Chromosomes

Genes are packaged in bundles called Genes are packaged in bundles called chromosomes. chromosomes.

Humans have 23 pairs of chromosomes (for a Humans have 23 pairs of chromosomes (for a total of 46).total of 46).

Of those, 1 pair is the sex chromosomes Of those, 1 pair is the sex chromosomes (determines whether you are male or female, (determines whether you are male or female, plus some other body characteristics), and the plus some other body characteristics), and the other 22 pairs are autosomal chromosomesother 22 pairs are autosomal chromosomes

Human chromosomeHuman chromosome

22.pairs of autosomes22.pairs of autosomes 1 pair of allosomes or sex chromosomes1 pair of allosomes or sex chromosomes

Chromosome- structureChromosome- structure

DNADNA

Autosomes & allosomesAutosomes & allosomes

Sex chromosomesSex chromosomes There are also two chromosomes that have been givenThere are also two chromosomes that have been given the letters X and Y: these are the the letters X and Y: these are the sex chromosomessex chromosomes. The X. The X chromosome is much larger than the Y chromosome.chromosome is much larger than the Y chromosome. Women Women have• 46 chromosomes (44 autosomes plus two have• 46 chromosomes (44 autosomes plus two

copies of the X chromosome) in their body cells: 46,XXcopies of the X chromosome) in their body cells: 46,XX • • 23 chromosomes (22 autosomes plus an X chromosome) in23 chromosomes (22 autosomes plus an X chromosome) in their egg cellstheir egg cells Men Men have• 46 chromosomes (44 autosomes plus an X and a Yhave• 46 chromosomes (44 autosomes plus an X and a Y chromosome) in their body cells: 46,XYchromosome) in their body cells: 46,XY • • 23 chromosomes (22 autosomes plus an X or Y 23 chromosomes (22 autosomes plus an X or Y

chromosome)chromosome) in their sperm cellsin their sperm cells

Female and Male childrenFemale and Male children

XX-Female XY- MaleXX-Female XY- Male

Human chromosomes Human chromosomes

Human Y chromosomeHuman Y chromosome

Human Y chromosomeHuman Y chromosome In humans, the Y In humans, the Y

chromosome spans 58 chromosome spans 58 million million base pairsbase pairs (the  (the building blocks of building blocks of DNADNA) )

.Represents approximately .Represents approximately 0.38% of the total DNA in 0.38% of the total DNA in a human a human cellcell..

The human Y chromosome The human Y chromosome contains 86contains 86[8][8] genes,  genes, which code for only 23 which code for only 23 distinct proteins. distinct proteins.

Traits that are inherited via Traits that are inherited via the Y chromosome are the Y chromosome are called holandric traitscalled holandric traits

Character of YCharacter of Y The human Y chromosome is unable to recombine The human Y chromosome is unable to recombine

with the X chromosome, except for small pieces of with the X chromosome, except for small pieces of pseudoautosomalpseudoautosomal regions regions at the  at the telomerestelomeres (which  (which comprise about 5% of the chromosome's length). comprise about 5% of the chromosome's length).

These regions are relics of ancient These regions are relics of ancient homologyhomology between  between the X and Y chromosomes. the X and Y chromosomes.

The bulk of the Y chromosome which does not The bulk of the Y chromosome which does not recombine is called the "NRY" or non-recombining recombine is called the "NRY" or non-recombining region of the Y chromosomeregion of the Y chromosome

  It is the It is the SNPsSNPs in this region which are used for  in this region which are used for tracing direct paternal ancestral linestracing direct paternal ancestral lines

ChromosomesChromosomes

Origin of chromosomesOrigin of chromosomes The mammalian sex chromosomes are thought to The mammalian sex chromosomes are thought to

have arisen from an ordinary pair of autosomes have arisen from an ordinary pair of autosomes ~300 million years ago.~300 million years ago.

Until then, ambient temperature during embryonic Until then, ambient temperature during embryonic development might have determined the sex of development might have determined the sex of mammalian ancestors, as in many modern reptiles mammalian ancestors, as in many modern reptiles and other descendants of bony fish.and other descendants of bony fish.

The foremost sex chromosome bearers are, notably, The foremost sex chromosome bearers are, notably, birds and mammals. birds and mammals.

Our lifeOur life

Our lifeOur life

All of the 20,000 or so genes contain a All of the 20,000 or so genes contain a different `packet’ of information necessary for different `packet’ of information necessary for our bodies to grow and work. our bodies to grow and work.

Our genes also contain the information for Our genes also contain the information for how we look: the colour of our eyes, how tall how we look: the colour of our eyes, how tall we are, the shape of our nose, etc. we are, the shape of our nose, etc.

The information is in the form of a chemical The information is in the form of a chemical (DNA) code (the (DNA) code (the genetic codegenetic code

Our lifeOur life

Genes Genes

Each of these beads is called a Each of these beads is called a genegene Each gene is a piece of genetic informationEach gene is a piece of genetic information Thousands of genes make up each chromosomeThousands of genes make up each chromosome Since the chromosomes come in pairs, there are two Since the chromosomes come in pairs, there are two

copies of the genes. copies of the genes. The exception to this rule applies to the genes carried The exception to this rule applies to the genes carried

on the sex chromosomes: the X and Y.on the sex chromosomes: the X and Y. Since men have only one copy of the X chromosome, Since men have only one copy of the X chromosome,

they have only one copy of all the genes carried on they have only one copy of all the genes carried on the X chromosome the X chromosome

Human GenomeHuman Genome

The human genome is a complete copy of the The human genome is a complete copy of the entire set of human gene instructions. entire set of human gene instructions. 

The Human Genome ProjectThe Human Genome Project, completed in , completed in 2003, identified all the human genes in DNA 2003, identified all the human genes in DNA and stored the information in databases so all and stored the information in databases so all researchers everywhere could use it.researchers everywhere could use it.

Number of GenesNumber of Genes Our genes have an important role in our cellsOur genes have an important role in our cells Each gene has its own specific location on the chromosome and Each gene has its own specific location on the chromosome and

is a piece of the genetic material that does one particular job.is a piece of the genetic material that does one particular job. A gene is a distinct portion of a cell’s DNA. Genes are coded A gene is a distinct portion of a cell’s DNA. Genes are coded

instructions for making everything the body needs, especially instructions for making everything the body needs, especially proteins. Human beings have about 25,000 genes. •proteins. Human beings have about 25,000 genes. •

The DNA code is made up of very long chains of four chemical The DNA code is made up of very long chains of four chemical ‘letters’: ‘letters’: AAdenine (A), denine (A), GGuanine (G), uanine (G), TThymine (T) andhymine (T) and

CCytosine (C)ytosine (C) – – In the DNA information, each ‘word’ is a combination of three In the DNA information, each ‘word’ is a combination of three

of these four chemical ‘letters’ A, G, C and Tof these four chemical ‘letters’ A, G, C and T – – Each three-letter word (Each three-letter word (triplettriplet) tells the cell to produce a ) tells the cell to produce a

particular amino acid that form proteinsparticular amino acid that form proteins

Chromosomes & genesChromosomes & genes

GeneGene

A gene is a distinct portion of a cell’s DNA. Genes A gene is a distinct portion of a cell’s DNA. Genes are coded instructions for making everything the are coded instructions for making everything the body needs, especially proteins. Human beings have body needs, especially proteins. Human beings have about 25,000 genes. about 25,000 genes.

Our genes also contain the information for Our genes also contain the information for how we look: the colour of our eyes, how tall how we look: the colour of our eyes, how tall we are, the shape of our nose, etc. we are, the shape of our nose, etc.

The information is in the form of a chemical The information is in the form of a chemical (DNA) code (the (DNA) code (the genetic codegenetic code

Gene Gene

Our genes have an Our genes have an important role in our important role in our cellscells

Each gene has its own Each gene has its own specific location on the specific location on the chromosome and is a chromosome and is a piece of the genetic piece of the genetic material that does one material that does one particular jobparticular job

DNA- InformationDNA- Information The DNA code is made up of very long chains of four The DNA code is made up of very long chains of four

chemical ‘letters’: chemical ‘letters’: AAdenine (A), denine (A), GGuanine (G), uanine (G), TThymine (T) and hymine (T) and CCytosine (C) – In the DNA ytosine (C) – In the DNA information, each ‘word’ is a combination of three of information, each ‘word’ is a combination of three of these four chemical ‘letters’ A, G, C and Tthese four chemical ‘letters’ A, G, C and T

– – Each three-letter word (Each three-letter word (triplettriplet) tells the cell to ) tells the cell to produce a particular amino acid that form proteins – produce a particular amino acid that form proteins – The sequence of three-letter words in the gene The sequence of three-letter words in the gene enables the cells to assemble the amino acids in the enables the cells to assemble the amino acids in the correct order to make up a proteincorrect order to make up a protein

DNADNA – –

Different genes are active in different cell types, Different genes are active in different cell types, tissues and organs, producing the necessary specific tissues and organs, producing the necessary specific proteins; some genes are ‘switched off’ and others are proteins; some genes are ‘switched off’ and others are ‘switched on Changes to the genetic code can mean ‘switched on Changes to the genetic code can mean that a particular protein is not produced properly, that a particular protein is not produced properly, produced in the wrong amounts or not produced at allproduced in the wrong amounts or not produced at all

In some cases, the change in the genetic code can In some cases, the change in the genetic code can result in a genetic condition, affecting our growth, result in a genetic condition, affecting our growth, development and how our bodies workdevelopment and how our bodies work

Human chromosomesHuman chromosomes

Human Chrosomes - crossing overHuman Chrosomes - crossing over

Human XY chromosomesHuman XY chromosomes

Human sex chromosomesHuman sex chromosomes XX & XY XX & XY

Human sex chromosomsHuman sex chromosoms

XYXY

MutationMutation

The particular order of the pairs of As, Ts, Cs, The particular order of the pairs of As, Ts, Cs, and Gs is extremely important in the DNA. and Gs is extremely important in the DNA. Sometimes there is a mistake — one of the Sometimes there is a mistake — one of the pairs gets switched, dropped, or repeated. This pairs gets switched, dropped, or repeated. This changes the coding for one or more genes. changes the coding for one or more genes. This is called genetic mutation. A mutation This is called genetic mutation. A mutation maybe disease-causing or harmless.maybe disease-causing or harmless.

Y Chromosomes evolution in Y Chromosomes evolution in AnimalsAnimals

Y is declining Y is declining

Degeneration of YDegeneration of Y Both sex chromosomes have the same origin Both sex chromosomes have the same origin

evolutionary mechanisms which allowed the Y evolutionary mechanisms which allowed the Y chromosome to shrink – that is still debatable. chromosome to shrink – that is still debatable.

Simulations have shown that the strategy of sexual Simulations have shown that the strategy of sexual reproduction (more explicitly the promiscuity of reproduction (more explicitly the promiscuity of women) is responsible for shrinking of Y women) is responsible for shrinking of Y chromosome, chromosome,

, when woman (XX) can freely choose a man (XY) as , when woman (XX) can freely choose a man (XY) as a partner for reproduction from the whole population a partner for reproduction from the whole population of males, the Y chromosome accumulates defects and of males, the Y chromosome accumulates defects and eventually the only information it brings is a male sex eventually the only information it brings is a male sex determinationdetermination

Dunnart – marsupial..4 genesDunnart – marsupial..4 genes

Degeneration of Y-why?Degeneration of Y-why?

when woman (XX) can freely choose a man (XY) as a partner when woman (XX) can freely choose a man (XY) as a partner for reproduction from the whole population of males, the Y for reproduction from the whole population of males, the Y chromosome accumulates defects and eventually the only chromosome accumulates defects and eventually the only information it brings is a male sex determination information it brings is a male sex determination The The fraction of males is less important or even fraction of males is less important or even unimportant, because after conception the male unimportant, because after conception the male partners are returning to the pool. Thus, one male can partners are returning to the pool. Thus, one male can be a father of many offspring of different females. As be a father of many offspring of different females. As a result of shrinking Y chromosome, the males a result of shrinking Y chromosome, the males become hemizygous in respect to the X chromosome become hemizygous in respect to the X chromosome content (have only one copy – half of information content (have only one copy – half of information possessed by females in the X chromosome) and are possessed by females in the X chromosome) and are characterized by higher mortality, observed in the characterized by higher mortality, observed in the human populations. If it is assumed in the model that human populations. If it is assumed in the model that the the

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