lab6 cytogenetics.ppt

8/11/2019 lab6 cytogenetics.ppt

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Lab No ( 6 )

Human cytogenetics


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Human genome

The human genome is the genome ofHomo sapiens , which is stored on 23chromosome pairs (46 in total ), each ofwhich contain hundreds of genes separated by intergenic regions .

Twenty-two of these are autosomalchromosome pairs , while the remainingpair is sex-determining .
http://en.wikipedia.org/wiki/Genomehttp://en.wikipedia.org/wiki/Homo_sapienshttp://en.wikipedia.org/wiki/Geneshttp://en.wikipedia.org/wiki/Autosomehttp://en.wikipedia.org/wiki/Autosomehttp://en.wikipedia.org/wiki/XY_sex-determination_systemhttp://en.wikipedia.org/wiki/XY_sex-determination_systemhttp://en.wikipedia.org/wiki/XY_sex-determination_systemhttp://en.wikipedia.org/wiki/XY_sex-determination_systemhttp://en.wikipedia.org/wiki/Autosomehttp://en.wikipedia.org/wiki/Autosomehttp://en.wikipedia.org/wiki/Geneshttp://en.wikipedia.org/wiki/Homo_sapienshttp://en.wikipedia.org/wiki/Genome


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Genes and inheritance

Genes are inherited as units, with parents dividing outtheir genes to their offspring.

Humans have two copies of each of their genes andwhen people reproduce they make copies of theirgenes in eggs or sperm, but only put in one copy ofeach type of gene. An egg then joins with a sperm togive a child with a new set of genes. This child willhave the same number of genes as its parents but forany gene one of their two copies will come from thefather, and one from the mother.


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Not all the genes for a particular instruction are exactlythe same. Different forms of one type of gene are calleddifferent alleles of that gene.

As an example, one allele of a gene for hair color could

carry the instruction to produce a lot of the pigment inblack hair, while a different allele could give a garbledversion of this instruction, so that no pigment is producedand the hair is white.Mutations are random events that change the sequenceof a gene and therefore create a new allele. Mutationscan produce a new trait, such as turning an allele forblack hair into an allele for white hair. The appearance ofnew traits is important in evolution
http://en.wikipedia.org/wiki/Allelehttp://en.wikipedia.org/wiki/Mutationhttp://en.wikipedia.org/wiki/Introduction_to_evolutionhttp://en.wikipedia.org/wiki/Introduction_to_evolutionhttp://en.wikipedia.org/wiki/Mutationhttp://en.wikipedia.org/wiki/Allele


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Genetic information is carried by a long molecule calledDNA and this DNA is copied and inherited acrossgenerations.Traits are carried in DNA as instructions for constructing

and operating an organism. These instructions arecontained in segments of DNA called genes .DNA is made of a sequence of simple units, with theorder of these units spelling out instructions in thegenetic code . This is similar to the orders of lettersspelling out words. The organism "reads" the sequenceof these units and decodes the instruction.
http://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Genetic_codehttp://en.wikipedia.org/wiki/Genetic_codehttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/DNA


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Karyotype

A karyotype is the characteristicchromosome complement of a eukaryote species . The preparation and study ofkaryotypes is part of cytogenetics .
http://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Cytogeneticshttp://en.wikipedia.org/wiki/Cytogeneticshttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Chromosome


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Most (but not all) species have a standardkaryotype. The normal human karyotypescontain 22 pairs of autosomal chromosomesand one pair of sex chromosomes .Normal karyotypes for women contain two Xchromosomes and are denoted 46,XX; men have both an X and a Y chromosome denoted46,XY. However, some individuals have other

karyotypes with added or missingchromosomes, and in most cases there aredevelopmental abnormalities as a

consequence.
http://en.wikipedia.org/wiki/Sex_chromosomeshttp://en.wikipedia.org/wiki/Womenhttp://en.wikipedia.org/wiki/X_chromosomehttp://en.wikipedia.org/wiki/X_chromosomehttp://en.wikipedia.org/wiki/Menhttp://en.wikipedia.org/wiki/Y_chromosomehttp://en.wikipedia.org/wiki/Y_chromosomehttp://en.wikipedia.org/wiki/Menhttp://en.wikipedia.org/wiki/X_chromosomehttp://en.wikipedia.org/wiki/X_chromosomehttp://en.wikipedia.org/wiki/Womenhttp://en.wikipedia.org/wiki/Sex_chromosomes


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Karyotypes objectives

Can be used for many purposes.They may be used:

1- To study chromosomal aberrations .2- To study cellular function.3- To study taxonomic relationships.

4- To gather information about pastevolutionary events.
http://en.wikipedia.org/wiki/Chromosomal_aberrationhttp://en.wikipedia.org/wiki/Cell_biologyhttp://en.wikipedia.org/wiki/Taxonomichttp://en.wikipedia.org/wiki/Evolutionaryhttp://en.wikipedia.org/wiki/Evolutionaryhttp://en.wikipedia.org/wiki/Taxonomichttp://en.wikipedia.org/wiki/Cell_biologyhttp://en.wikipedia.org/wiki/Chromosomal_aberration


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Observations on karyotypes

Six different characteristics of karyotypes areusually observed and compared:

1- differences in absolute sizes of chromosomes.2- differences in the position of centromeres . This

is brought about by translocations .3- differences in relative size of chromosomes

can only be caused by segmental interchangeof unequal lengths.
http://en.wikipedia.org/wiki/Centromereshttp://en.wikipedia.org/wiki/Translocationshttp://en.wikipedia.org/wiki/Translocationshttp://en.wikipedia.org/wiki/Centromeres


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4- differences in basic number of chromosomesmay occur due to successive unequaltranslocations which finally remove all theessential genetic material from a chromosome.

5- differences in number and position of satellites,which (when they occur) are small bodiesattached to a chromosome by a thin thread.

6- differences in degree and distribution of

heterochromatic regions. Heterochromatin stainsdarker than euchromatin , indicating tighterpacking, and mainly consists of geneticallyinactive repetitive DNA sequences.
http://en.wikipedia.org/wiki/Heterochromatinhttp://en.wikipedia.org/wiki/Euchromatinhttp://en.wikipedia.org/wiki/Euchromatinhttp://en.wikipedia.org/wiki/Heterochromatin


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Types of banding

Cytogenetics employs several techniques tovisualize different aspects of chromosomes:G-banding is obtained with Giemsa stain .R-banding is the reverse of G-banding (the Rstands for "reverse").C-banding: Giemsa binds to constitutiveheterochromatin , so it stains centromeres .

Q-banding is a fluorescent pattern obtainedusing quinacrine for staining. The pattern ofbands is very similar to that seen in G-banding.

T-banding: visualize telomeres .
http://en.wikipedia.org/wiki/Cytogeneticshttp://en.wikipedia.org/wiki/Giemsahttp://en.wikipedia.org/wiki/Constitutive_heterochromatinhttp://en.wikipedia.org/wiki/Constitutive_heterochromatinhttp://en.wikipedia.org/wiki/Centromerehttp://en.wikipedia.org/wiki/Fluorescenthttp://en.wikipedia.org/wiki/Telomerehttp://en.wikipedia.org/wiki/Telomerehttp://en.wikipedia.org/wiki/Fluorescenthttp://en.wikipedia.org/wiki/Centromerehttp://en.wikipedia.org/wiki/Constitutive_heterochromatinhttp://en.wikipedia.org/wiki/Constitutive_heterochromatinhttp://en.wikipedia.org/wiki/Giemsahttp://en.wikipedia.org/wiki/Cytogenetics


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Karyotypes are arranged with the shortarm of the chromosome on top, and thelong arm on the bottom. Some karyotypes

call the short and long arms p and q ,respectively.In addition, the differently stained regionsand sub-regions are given numericaldesignations from proximal to distal on thechromosome arms.
http://en.wikipedia.org/wiki/Proximalhttp://en.wikipedia.org/wiki/Distalhttp://en.wikipedia.org/wiki/Distalhttp://en.wikipedia.org/wiki/Proximal


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HUMAN MALENORMAL KARYOTYPE


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HUMAN FEMALENORMAL KARYOTYPE


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Chromosome abnormalities

Chromosome abnormalities can be:

1- numerical, as in the presence of extra or missing chromosomes,or :

structural, as in translocations ,

Numerical abnormalities, also known as aneuploidy , often occur as a resultof nondisjunction during meiosis in the formation of a gamete ; trisomies , inwhich three copies of a chromosome are present instead of the usual two,are common numerical abnormalities.

Structural abnormalities often arise from errors in homologousrecombination . Both types of abnormalities can occur in gametes and therefore will bepresent in all cells of an affected person's body, or they can occur duringmitosis and give rise to a genetic mosaic individual who has some normaland some abnormal cells.
http://en.wikipedia.org/wiki/Chromosomal_translocationhttp://en.wikipedia.org/wiki/Aneuploidyhttp://en.wikipedia.org/wiki/Nondisjunctionhttp://en.wikipedia.org/wiki/Meiosishttp://en.wikipedia.org/wiki/Gametehttp://en.wikipedia.org/wiki/Trisomyhttp://en.wikipedia.org/wiki/Homologous_recombinationhttp://en.wikipedia.org/wiki/Homologous_recombinationhttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Genetic_mosaichttp://en.wikipedia.org/wiki/Genetic_mosaichttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Homologous_recombinationhttp://en.wikipedia.org/wiki/Homologous_recombinationhttp://en.wikipedia.org/wiki/Trisomyhttp://en.wikipedia.org/wiki/Gametehttp://en.wikipedia.org/wiki/Meiosishttp://en.wikipedia.org/wiki/Nondisjunctionhttp://en.wikipedia.org/wiki/Aneuploidyhttp://en.wikipedia.org/wiki/Chromosomal_translocation


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A chromosomal translocation as revealed bytwo different karyotyping techniques


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Dawn Syndrome


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Chromosomal abnormalities that lead to disease inhumans include:Turner syndrome results from a single X

chromosome (45, X or 45, X0).Klinefelter syndrome , the most common malechromosomal disease, otherwise known as 47,XXY is caused by an extra X chromosome.

Edwards syndrome is caused by trisomy (threecopies) of chromosome 18.Down syndrome , a common chromosomal disease,is caused by trisomy of chromosome 21.Patau syndrome is caused by trisomy ofchromosome 13.

Also documented are trisomy 8, trisomy 9 andtrisomy 16, although they generally do not surviveto birth.
http://en.wikipedia.org/wiki/Turner_syndromehttp://en.wikipedia.org/wiki/Klinefelter_syndromehttp://en.wikipedia.org/wiki/Edwards_syndromehttp://en.wikipedia.org/wiki/Trisomyhttp://en.wikipedia.org/wiki/Down_syndromehttp://en.wikipedia.org/wiki/Patau_syndromehttp://en.wikipedia.org/wiki/Patau_syndromehttp://en.wikipedia.org/wiki/Down_syndromehttp://en.wikipedia.org/wiki/Trisomyhttp://en.wikipedia.org/wiki/Edwards_syndromehttp://en.wikipedia.org/wiki/Klinefelter_syndromehttp://en.wikipedia.org/wiki/Turner_syndrome


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Translocation_Down_syndrome


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lab6 cytogenetics.ppt

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