Idiogram and KARYOTYPING

Prepared by

SanmaN

karyology

The study of whole sets of chromosomes is sometimes known as karyology.

What is Idiogram ???

Diagrammatic representation of the gametic chromosome set (n) of a species

Used to compare the karyotype of one species with the other

Karyotype is represented diagrammatically showing all the morphological features of chromosomes.

What is Karyotyping

a standard chart of chromosomes isolated from a cell at metaphase arranged in order by size and structure of physical landmark

The basic number of chromosomes in the somatic cells of an individual or a species is called the somatic number and is designated 2n. Thus, in humans 2n = 46. In the germ-line (the sex cells) the chromosome number is n (humans: n = 23)

Why do scientists look at chromosomes??

Scientists can diagnose or predict genetic disorders by looking at chromosomes.

This kind of analysis is used in prenatal testing and in diagnosing certain disorders, such as Down syndrome, or in diagnosing a specific types of

leukemia.

SPECIMENS USED

Peripheral Blood Cultured Skin Fibroblast

Bone Marrow Amniotic Fluid

How are chromosomes classified?

According to the site of the centromere According to size

How are Chromosomes of similar size and shape distinguished from one another?Chromosome Banding (Q banding,G banding C banding, R banding)

CENTROMERE POSITIONS

CENTROMERE POSITIONS

Submetacentric Metacentric

Telocentri Acrocentric

CLASSIFICATION OF CHROMOSOMES FOR KARYOTYPING

Group A: chromosomes 1,2,3 largest

metacentric and submetacentric

Group B: chromosomes 4,5 large submetacentric

Group C: chromosomes 6,7,8,9,10,11,12mediumsubmetacentric

CLASSIFICATION OF CHROMOSOMES FOR KARYOTYPING

Group D: chromosomes 13, 14, 15 medium acrocentric

Group E: chromosomes 16, 17, 18 short metacentric or submetacentric

Group F: chromosomes 19, 20 short metacentric

Group G: chromosomes 21, 22 very short acrocentric

Preparing a Karyotype

Incubate 3-4 days

Add chemical to stop mitosis in metaphase

Lymphocytes are harvested and treated with hypotonic solution

Swollen cells are fixed, dropped in a glass slide, dried and stained

Types of banding

G-banding is obtained with Giemsa stain following digestion of chromosomes with trypsin. It yields a series of lightly and darkly stained bands - the dark regions tend to be heterochromatic, late-replicating and AT rich. The light regions tend to be euchromatic, early-replicating and GC rich. This method will normally produce 300-400 bands in a normal, human genome.

R-banding is the reverse of G-banding (the R stands for "reverse"). The dark regions are euchromatic (guanine-cytosine rich regions) and the bright regions are heterochromatic (thymine-adenine rich regions).

C-banding: Giemsa binds to constitutive heterochromatin, so it stains centromeres.

Q-banding is a fluorescent pattern obtained using quinacrine for staining. The pattern of bands is very similar to that seen in G-banding.

T-banding: visualize telomeres.

Silver staining: Silver nitrate stains the nucleolar organization region-associated protein. This yields a dark region where the silver is deposited, denoting the activity of rRNA genes within the NOR

The human karyotype

The normal human karyotypes contain 22 pairs of autosomal chromosomes and one pair of sex chromosomes. Normal karyotypes

for females contain two X chromosomes and are denoted 46,XX; males have both an X and a Y chromosome denoted 46,XY. Any variation from the standard karyotype may lead to developmental abnormalities.

Karyotype

MALE KARYOTYPE FEMALE KARYOTYPE

Digital karyotyping

Digital karyotyping is a technique used to quantify the DNA copy number on a genomic scale. Short sequences of DNA from specific loci all over the genome are isolated and enumerated.This method is also known as virtual karyotyping.

Chromosomal abnormalities that can be detected by karyotyping

Autosomal Sex chromosomal

Nmerical Abration

Euploidy Monosomy (n) Diploidy (2n) Triploidy (3n) Tetraploidy (4n)

Aneuploidy Hyperploidy

Trisomy (2n+1)

Tetrasomy (2n+2)

Hypoploidy Monosomy (2n-1) Nullsomy (2n-2)

Ploidy

Polyploidy, where there are more than two sets of homologous chromosomes in the cells

Polyploid series in related species which consist entirely of multiples of a single basic number are known as euploid

Polyploidy in lower plants (ferns, horsetails andpsilotales) is also commonIt is not occuring in humans..It indicate genetical abnormality

Aneuploidy

Aneuploidy is a term used to describe a chromosome problem, such as Down syndrome, that is caused by an extra or missing chromosome.

This would give rise to achromosome abnormality such as an extra chromosome or one or more chromosomes lost. Abnormalities in chromosome number usually cause a defect in development. Down syndrome and Turner syndrome are examples of this.

Condition Syndrome

Trisomy-21 Down

Trisomy-18 Edward

Trisomy-13 Patau

Autosomal Syndromes

Sex chromosomal syndrome

XXY Klinefelter

XYY Jacobs

XXX Superfemale

XO Turner

Thank you

M.Sc Human genetics

School of science

Gujrat uni. Ahm