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GENETICS

MRCOG1

MRCOG 1 GENETICS- (MEDHOME)

+92 301 4843695
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MRCOG 1 GENETICS -(MEDHOME)

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MRCOG 1 GENETICS -(MEDHOME)

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MRCOG 1 GENETICS -(MEDHOME)

SUBJECT OUTLINE

q Chromosomes, genes and cell division

q Principles of inheritance
q
q Prenatal genetics
Genetics of gynaecological malignancies

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Genes Each chromosome is composed of tightly coiled
Codon -genetic code

threads of DNA organised around proteins called
made of RNA-Total

histones A gene is a specific sequence of DNA that
are 64-each codon -

carries the instructions for the construction of a protein make one sp AA
The human genome is estimated to contain

approximately
20 ,000 genes.

ALLELE is a length of DNA
that carries information to
make
a single peptide chain.-
made of 2 regions
introns -non coding rea
Exons -coding area

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linked by 3′-5′ phosphodiester bond.
5′ end of incoming nucleotide bears the
triphosphate (energy source for the bond).

α-Phosphate is target of 3′ hydroxyl attack.

qAmino acids necessary for purine synthesis (cats purr

until they GAG):

qGlycine

qAspartate

qGlutamine SUBMETACENTRIC REST ALL


METACENRIC
1,3--19,20


ACROCENRIC 21-22-13-14-15
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Chromosomes, genes and cell division :

q Chromosomes Each human somatic cell has 23 pairs of chromosomes that are
distinguished according to their length and pattern of light and dark bands.

q
Each chromosome has a centromere (a constriction along its length), which
divides the chromosome into short and long arms known as the p and q arms,

respectively
1. When the short and long arms are of approximately equal length, the
chromosome is known as a metacentric chromosome.




2.When the centromere divides the chromosome into two arms where one arm

is obviously longer than the other, the chromosome is known as a
submetacentric chromosome.

3.When the centromere is situated at the top of the chromosome, the
chromosome is known as an acrocentric chromosome.

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HUMAN CHROMOSOMES -7 GROUPS (SMALLEST IS 22-LARGEST 1)-DETECTED AT
METAPHASE SUBMETACENTRIC REST ALL
METACENRIC 1,3--19,20
ACROCENRIC 21-22-13-14-15
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Isochrome refers to an abnormal
The normal Y chromosome is a submetacentric
chromosome created as a result of
chromosome.The long arm of Y chromosome has

mutation. In this chromosome,
variable length.
transverse rather than normal

longitudinal splitting of replicating

chromosomes occurs. As a result, two

chromosomes having
both identical arms are formed

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Y chromosome contains the SRY gene on its short arm,

which elicits the development of male gonad (testis).

This can be considered as the gene of maleness, which

specifies male gonads and male features. Genetic
males having XY karyotype, but with a mutation or

deletion of this SRY gene on the Y chromosome, will be

phenotypically females despite the presence of most of

the part of Y chromosome.

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The Lyon Hypothesis

Lyon’s hypothesis does not relate to germ cells.
Both the X chromosomes of maternal and paternal origin can

be inactivated in each cell. According to the Lyon’s

hypothesis, only the terminal portion of the p arm of the X

chromosome remains active.
The process of inactivation occurs early in embryonic life,

probably by day 16.
The inactive chromosome is known as the Barr body
The Barr body is seen in up to 30% of cells on a buccal smear

from a woman.
It is also seen in neutrophils on a blood film in the form of

“drumstick”.

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LABRATORY TECHIQUES
PROTEMICS -QUANTITATIVE & QUALITITATIVE

COMPARISON OF PROTEINS
(2 DIEMSNIOSN GEL ELECTROPHOERSIS )
•1-VOLTAGE PG GRADIENT
•2ND-VOLTAGE PERPENDICULAR

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•CELL DIVISION

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Chromosomes, Genes and Cell Division

There are 46 chromosomes (23 pairs) in each somatic cell; this is the diploid

number.
There are 23 individual chromosomes, one from each chromosome pair, in the ova

and sperm; this is the haploid number.

The chromosomes contain approximately 20 000 genes.
Genes code for the production of specific proteins. Mitosis is the process
whereby somatic cells divide. The progenitor cell has 46 chromosomes and each
daughter cell has 46 chromosomes.
Meiosis occurs in the generation of germ cells. It has two distinct phases:

A. During meiosis I, chromosomes duplicate, paternally and maternally inherited
chromosomes are recombined and the diploid number is reduced to the haploid
number.
B. During meiosis II, splitting of sister chromatids occurs. Therefore, by the end of
meiosis, four daughter cells are generated from one dividing germ cell, paternal
and maternal genetic material is mixed and each germ cell has only 23
chromosomes.

Thus, by the end of meiosis, four daughter cells are generated from each
dividing germ cell.
Each of these daughter cells should have 23 individual chromosomes,
representing one chromosome from each pair of autosomes in addition to an
X chromosome in ova and either an X chromosome or a Y chromosome in
sperm.
As a result of recombination during meiosis I, each germ cell will have a
unique combination of both paternally and maternally inherited genes.
Of note, in female meiosis, three of the daughter cells constitute polar bodies
and will not survive; only one daughter cell becomes an ovum. By contrast, all
four daughter cells produced from male meiosis develop into spermatozoa.

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The first 22 pairs of chromosomes are known as autosomes and have
been designated the numbers 1 through to 22 depending upon the
decreasing relative length of the chromosome pairs. The composition of
the 23rd pair of chromosomes, the sex chromosomes, determines a
person's gender with female individuals having two X chromosomes
and male individuals having an X and a Y chromosome.
In the creation of germ cells, the number of chromosomes is halved so
that each ovum and spermatozoon contains only one chromosome
from each pair.

Germ cells therefore have 23 chromosomes, known as the haploid
number
whereas somatic cells have 46 chromosomes, referred to as the diploid
number.

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Mitosis
When somatic cells divide, they go through a
process known as mitosis, whereby the cell
duplicates its DNA and cleaves to generate two
identical daughter cells with 23 pairs, or the diploid
number, of chromosomes

Meiosis

By contrast, when germ cells divide to produce ova or sperm, they
undergo meiosis. Meiosis is unique to the germ cells and is
essential to reduce the somatic diploid number of 46
chromosomes to the haploid number of 23 chromosomes . This
reduction ensures that, when fertilisation occurs, the zygote has
46 chromosomes rather than 92, which would be the result of
fertilisation involving two diploid germ cells.
Meiosis consists of two consecutive division cycles that are
designated meiosis I and meiosis II

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In Prophase 1 of meiosis, Chromosomes
become shorter and thicker, clearly visible in a
microscope. The nucleus disappears during
this phase. It has five phases-

1. Leptotene - The chromosomes condense and
are visible under an electron microscope.
2. Zygotene - It is the sub-stage, where
synapsis between homologous chromosomes
begins.
3. Pachytene - Crossing over starts within the
bivalents. The synaptonemal complex is
complete, allowing chiasma to form.
4. Diplotene - The synaptonemal complex
degrades and homologous chromosomes
separate from one another a little.
5. Diakinesis - Chromosomes condense further
during this stage. The four parts of the tetrads
are actually visible.

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CONDENSE REPLICATION CALLGN IN ENTRE-S

SEPARATION-MOVE TO OPPOSITE POLE

ENVELOP BREAK DOWN

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A. During prophase the chromosomes condense.
B. During metaphase sister chromatids produced by
DNA replication during the S phase become aligned
in the centre of the cell.
C. During anaphase the sister chromatids separate

and move to opposite poles of the mitotic
apparatus/spindle.
D. During telophase the nuclear envelope breaks

down and reforms around the segregated
chromosomes.
E.The final physical division of the cytoplasm to
yield two daughter cells is called cytokinesis.

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