i want you understand the information well and create 25 mutiple choice questions that covers different aspects of them with their model answer below each question . here are the information: Objectives:
1- Describe the structure of human
chromosomes
2- Classify types of chromosomes
according to certain features .
3- Summarize steps of karyotyping and
highlight its importance in medical
practice
4- Recognize & Interpret karyotypes of
some common genetics abnormalities
.Human ChromosomesType of CHROMOSOMES
1- In human cell, Each nucleus
contains 46 chromosomes present
in pairs (23 pairs).
A. 22 pairs of somatic (autosomes).
B. One pair of (sex chromosomes).• 22 pairs (autosomes) =
homologous pairs.
(Paired chromosomes with the same
length, shape, centromere location &
genes).
• One pair (sex
chromosomes) =
homologous in female XX
heterologous in male XY.
• Homologous pair = two
identical chromosomes.
i.e each has same genes at
the same places (locations
or locui )Sex Chromosomes
Sex Determination in HumansStructure of chromosome
➢Each chromosome (d-chromosome) consists of 2
identical, longitudinal halves.
➢ Each is called chromatid= (s) …….(d=double)&
(s=single).
➢ The 2 S-chromatides of each d-chromosome
are attached at point called centromere.
➢Arising from centromere arms (upper & lower
arm)Types of chromosomes
3 types of chromosomes according to the position of the
centromeres:
1. Metacentric chromosome:
The centromere is median in position. The four
arms are equal in length
2. Submetacentric chromosome: The centromere is
closer to one of its end, Two short arms & two long
arms.
3. Acrocentric chromosome: The centromere is
present more near to its ends, Two very short and two
long arms.Types of Chromosomes
(According to centromere position)
In D-chromosomesKaryotyping
Karyotype is the study
of number & type of
chromosomes after its
arrangementThis arrangement depends
on:
- Length of the chromosomes
- Position of the centromere.
• Cells for chromosomal
study can be obtained
from white blood cells OR
skin biopsy, fetal cells from
amniotic fluid.Technique of karyotyping
1- Cultured cells arrested in metaphase stage
(maximally condensed chromosomes).by
colchicine which disrupting microtubules.
2- The condensed chromosomes of one nucleus
are photographed by light microscope after
staining then
3- rearranged digitally to produce a karyotype in
which stained chromosomes can be analyzedBanding pattern
Method to stain
different segments
genes with different
colors
- Study gene deletion
& translocationClinical importance of chromosomal
examination
➢Diagnosis of genetic sex .
➢Prenatal diagnosis of any genetic anomalies e.g
Down’s syndrome,& turner syndrome.
➢ In adult: Missing chromosomes or extra
chromosomes and chromosomal deletion or
translocation can be seen by new methods
(band technique)
4- Diagnosis of chronic myeloid leukemiaSex Chromatin
(Barr Body)
• A dark stained mass of chromatin, usually
adherent to the inner aspect of the nuclear
envelope of female somatic cells.
• A drumstick mass protruding from
the nucleus of neutrophils.
• Represents one of the two X chromosomes
which is inactive (condensed) in normal
female
• Seen in normal female cells.
• Absent in females with Turner’s syndrome XO.
• Seen in males with Klinefelter’s syndrome
XXY.
(Drum-stick in
Neutrophil)Why Barr body appears in female not
male?
➢ Since the normal male cell
contains only one XChromosome, and must be
Active.
The female cell contains two X
Chromosomes .Turner’s syndrome Klinefelter’s syndrome
Patient: Female Male
Has 2 X chromosomes
one is active & the
other is condensed
chromosomes abno:
(X0), only one sex
chromosome)active
No Barr body Barr body is presentCauses of Chromosomal Aberrations
1- Viral infection with German
measles during pregnancy :
causes fragmentation of
chromosomes.
3.Cytotoxic drugs
inhibit the formation
of mitotic spindle.
4- Pregnancy in
old women
2-Radiation:
causes some
chromosomal
damageTypes of chromosomal abnormalities
1. Numerical abnormalities:
Abnormal number of chromosomes, less or more
than 46 chromosomes.
2. Structural abnormalities:
Abnormalities in the structure of the
chromosomes (sequences of genes).A. Aberrations in chromosomal Number
1- Normally the number of chromosomes in
each sperm or ovum is 23 = haploid (n)
2- The normal number of chromosomes in a
zygote is 46 = diploid number (2n).
A- Polyploidy:
Addition of one or 2 complete haploid sets of
chromosomes.
B)- Aneuploid:
Addition or loss of one chromosome as: 45
or 47.Polyploidy
➢Triploidy:
Addition of one haploid set (23 chromosomes) to
the original cell chromosome(46), i.e (23+46)= 69
chromosomes.
➢ Tetraploidy:
Add of two haploid set (23+23 chromosomes)
to the original cell chromosome(46), i.e
(23+23+46)=92 chromosomes.Aneuploid
1- May occur in somatic or sex
chromosomes.
A- Trisomy syndrome :e.g
i- in autosomes
Down Syndromes(mongolism)
= Trisomy 21 i.e the cell contains 3
chromosome number 21 (46+1=
47chromosomes).Dawn’s Syndrome (47,+21)ii- In sex chromosomes :
1- Klinefelter's syndrome:
(47chromosomes): MALE having an extra
X chromosome (44 autosomes + XXY).
2-Multiple X syndrome:
(47 chromosomes): Female having an
extra X chromosome(44 autosomes
+XXX).ABBERATIONS
POLYPLOIDY
1-Triploidy
2- Tetraploidy
ANEUPLOID
Monosomy
syndrome
Turner’s
syndrome
Trisomy
Down
autoso
mes
sex
chromoso
mes
1-
klinefilter
2-Multiple
x
syndromesOr xx ovum +y spermKlinefelter’s syndrome 47,XXY
Or xx ovum +y spermB- Monosomy Syndrome
TURNER’S SYNDROME:
➢ FEMALE with only one sex
chromosome
➢(X0) (44 AUTOSOMES + XO)Xo Turner’s
syndrome• .Sex Chromosomal AbnormalitiesStructural Aberrations
(1-Deletion)2.Duplication
Addition of an extra part to an arm of
chromosome (double dose of genes on
one Chromosome).3. Translocation
Exchange of 2 pieces between non
homologues chromosomes e.g
Philadelphia syndrome exchange
occurs bet Chromosomes num (22 &9)4.Inversion: It occurs when a break happens
to one chromatid, the broken segments may
reattach again but in a inverted manner5. Isochromosomes:
sometimes, during cell division,
one chromosome may divide
transversely instead of
longitudinally
giving 2 unequal
chomosomes.Summary
1-in human cell, Each nucleus contains 46 chromosomes 22
pairs of somatic (autosomes).One pair of (sex
chromosomes).
2- There are three types of chromosomes according to the
position of the centromeres.
3- Karyotype is the study of number & type of
chromosomes after its arrangement.
4- Barr body represents the inactive (X) chromosomes
present in female cell .
5- There are types of chromosomal abnormalities1.