Human Chromosomes:Human Chromosomes:Genotype/PhenotypeGenotype/Phenotype

Muhammad Faiyaz-Ul-Haque, PhD, FRCPathMuhammad Faiyaz-Ul-Haque, PhD, FRCPath

Human Chromosomes:Human Chromosomes:Genotype/PhenotypeGenotype/Phenotype

Muhammad Faiyaz-Ul-Haque, PhD, FRCPathMuhammad Faiyaz-Ul-Haque, PhD, FRCPath

By the end of this lecture, the students should be able to:

Describe the number, structure, and classification of human chromosomes.

Explain what a Karyotype is and how it is obtained. Describe chromosomal banding and explain its

use. Describe the process of in situ hybridization and

the information it provides.

Lecture Objectives:Lecture Objectives:Lecture Objectives:Lecture Objectives:

G T A C T A

Chromosome

The order of bases in DNA is a code for making proteins. The code is read in groups of three

DNAGene

Cell machinery copies the code making an mRNA molecule. This moves into the cytoplasm.

Ribosomes read the code and accurately join Amino acids together to make a protein

AUG AGU AAA GGA GAA GAA CUU UUC ACU GGA UAG

M S E E LK G TF G

The protein folds to form its working shape

M

S EK G

E L TF G

M

S

E

K

GE L TF G

M

S

E

K

G

EL

TF

G

M

S

E

K

G

EL

TF

G

M

S

E

K

G

EL

T F

G

CELL

NUCLEUSM

S

E

K

G

EL

T F

G

T

G

M

S

E

K

G

EL

F

T

G

M

E

K

G

EL

FSGene ExpressionGene ExpressionGene ExpressionGene Expression

DNA->RNA->ProteinDNA->RNA->Protein

Nucleus

DNA bases

mRNA

DNA

Protein

Ribosome

Cell membrane

Gene

Chain of amino acids

Eukaryotic cellEukaryotic cellEukaryotic cellEukaryotic cell

■ Cytogenetics:

The study of the structure and function of chromosomes and chromosome behaviour during somatic and germline division

■ Molecular genetics:

The study of the structure and function of genes at a molecular level and how the genes are transferred from generation to generation.

GENETICS :GENETICS :GENETICS :GENETICS :

Cytogenetics: Cytogenetics: Cytogenetics: Cytogenetics:

Human Cytogenetics involves the study of human chromosomes in health and disease.

Chromosome studies are an important laboratory diagnostic procedure in1)prenatal diagnosis2)certain patients with mental retardation and multiple birth defects3)patients with abnormal sexual development4)some cases of infertility or multiple miscarriages5)in the study and treatment of patients with malignancies & hematologic disorders.

New techniques allow for increased resolution.

Spectral KaryotypeSpectral KaryotypeSpectral KaryotypeSpectral Karyotype

Human ChromosomesHuman Chromosomes

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15 16

17 18 19 20 21 22 X Y

Cytogenetics:■ Non-Banded Karyotype■ Banded Karyotype■ High resolution Karyotype

Molecular cytogenetics:■ Fluorescent in situ hybridization (FISH).

10-12 hrs.

6-8 hrs.

2-4 hrs.

Mitotic cell cycleMitotic cell cycleMitotic cell cycleMitotic cell cycle

Centromere

Telomere

Metacentric Submetacentric Acrocentric

Telomere

Arm

Longarm (q)

Shortarm (p)

Chromosome MorphologyChromosome Morphology

p

q

Arm Region Band Subband

2

1

1

2

21

1

12

3

4

3212154321

12

312312, 34123

17q11.2

Chromosome 17

Defining Chromosomal LocationDefining Chromosomal Location

Metaphase chromosomes: Metaphase chromosomes:

■ Each chromosome has a centromere (CEN), region which contains the kinetochore,

■ The 2 sister-chromatids are principally held together at the centromeric region.

■ CEN divides the chromosome into two arms: the short arm (p arm) and the long arm (q arm).

■ Each arm terminates in a telomere.

A single complete set of chromosomes. (N=23 for humans)

Centromeric position and arm length:Centromeric position and arm length:Centromeric position and arm length:Centromeric position and arm length:

The ratio of the lengths of the two arms is constant for each chromosome.

This ratio is an important parameter for chromosome identification and allows classification of chromosomes into several basic morphologic types: i-metacentric ii-sub-metacentric iii-acrocentric

In the human karyotype chromosome pairs 13, 14, 15, 21, 22 are acrocentric

Translocation Deletion

Insertion

Inversion Isochromosome

Ringchromosome

Derivativechromosome

Chromosome Structure Chromosome Structure AbnormalitiesAbnormalities

-22 pairs of autosomes, numbered from 1 to 22 by order of decreasing length

-1 pair of sex chromosomes: XX in the female, XY in the male.

Chromosomal classificationChromosomal classificationChromosomal classificationChromosomal classification

KaryotypingKaryotypingKaryotypingKaryotyping

Based on:1.the length2.the position of the centromere3.the presence or absence of satellites

A B

C

D E

G XF

46, XY 46, XX

■ Normal Karyotypes

Items in the Description Of Karyotype:Items in the Description Of Karyotype:Items in the Description Of Karyotype:Items in the Description Of Karyotype:

47, XY, + 21

45, XO,

■ Abnormal Karyotypes

Turner Syndrome

Down Syndrome

Visualizing Metaphase Visualizing Metaphase Chromosomes (Banding)Chromosomes (Banding)

• Giemsa-, reverse- or centromere-stained metaphase chromosomes

G-Bands R-Bands C-Bands

46, XY, t (9;22)(q34;q11)

Fluorescence In-Situ Hybridization Fluorescence In-Situ Hybridization (FISH)(FISH)

Fluorescence In-Situ Hybridization Fluorescence In-Situ Hybridization (FISH)(FISH)

Probe

Interphase or metaphasecells on slide (in situ)

Microscopicsignal (interphase)

Fluorescent Fluorescent in situin situ Hybridization (FISH)Hybridization (FISH)

Hybridization of complementary gene- or region-specific fluorescent probes to chromosomes.

FISH of interphase nuclei with a chromosome 21 centromeric

probe showing 3 signals consistent with trisomy 21

FISH of metaphase with a probe for telomere showing signals at

the end of each chromatid

Fluorescence In-Situ Hybridization Fluorescence In-Situ Hybridization (FISH)(FISH)

Fluorescence In-Situ Hybridization Fluorescence In-Situ Hybridization (FISH)(FISH)

Growth is a Complex ProcessGrowth is a Complex Process

FGFs (fibroblast growth factors) - instruct cells to differentiate into cartilage, not divide patterningDominant mutation in FGF receptor 3 is linked to achondroplasia(~95% of all dwarfs)

The packaging of DNA into chromosomes involves several orders of DNA coiling and folding.

The normal human karyotype is made up of 46 chromosomes consisting of 22 pairs of autosomes and a pair of sex chromosomes, XX in the female, and XY in the male.

Each chromosome consists of a short (p) and a long (q) arm joined at the centromere.

Molecular cytogenetic techniques (e.g. FISH) are based on the ability of DNA probes to attach with its complementary target sequence. They can be used to study chromosmes in metaphase or interphase.

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