Topics- Chromosomal Aberrations Multiple Alleles and blood groups Laws of Mendal.

1. GENETICS
UNIT – I
INTRODUCTION
Topics- Chromosomal Aberrations
Multiple Alleles and blood groups
Laws of Mendal
PRESENTED BY
Mrs. SOUMYA SUBRAMANI, M.Sc.(N)
LECTURER, MSN DEPARTMENT
CON- SRIPMS, COIMBATORE.

2. Chromosomal Aberrations
“Variation in chromosomal structure or number is called
Chromosomal Aberration”
They can refer to changes in the number of sets of
chromosomes (ploidy), changes in the number of individual
chromosomes (somy), or changes in appearance of individual
chromosomes through mutation-induced rearrangements. They can
be associated with genetic diseases or with species
differences
FISH and Banding techniques are used to
detect chromosomal aberrations.

3. Structural Aberrations
The chromosomal aberrations in which alternation of the
structure of chromosome (sequence of genes or kind of genes in
chromosome or no. of genes) occur—Structural Aberration.
Types of Structural Aberrations:
Changes in the numbers of genes


Deletion/ Deficiency (Terminal, Intercalary)
Duplication (Intrachromosomal, Interchromosomal)
 Changes in the location of genes


Inversions (Paracentric, Pericentric)
Translocations (Intrachromosomal, Interchromosomal)

5. Deletion
“Loss of a (generally small) segment of chromosome”
Spontaneously or may be induced (radiation, UV, chemicals, viruses).
Terminal deletion:
“Loss of either terminal segment of a chromosome”
Intercalary Deletion:
“Loss of segment in between centromere
and telomere”
A B C D E F G A B D E F G
C

6. Duplication
“Occurrence of a segment twice in the same chromosomes”
Intrachromosomal Duplication:
Tandem – in this case sequence of genes in the duplicated
segment is similar to the sequence of genes in the original segment
of a chromosome.
 Reverse tandem – the sequence of genes in the duplicated
segment is reverse to the sequence of genes in the original
segment of a chromosome.

7. Interchromosomal Duplication:
Displaced : Duplicating segment is incorporated away
from corresponding segment on the same chromosome.
Translocated: Duplicated chromosomal segment is
incorporated on different chromosome.
A B C D E F G A B C D E F F G

8. A B C D E F G H I J K
180O
A B C H G F E D I J K
“A chromosomal segment is oriented in a reverse position
(180o reversal )”
Paracentric Inversion:
“Inverted segment does not include centromere and
confined to one arm”
Pericentric Inversion:
“Included the centromere”
Inversion

9. Translocation
• “In translocation, change in position of the segment occurs in such a
way that they become integrated into same or homologous or non
homologous chromosome”
• Occurs spontaneously or may be induced by mutagens.

Types:
 Based on involvement of chromosomes:
Intrachromosomal Translocation:
 Intraradial: Shift occurs in same arm.
 Extraradial: Shift occurs in different arm.

10. Interchromosomal Translocation:
 Fraternal: Shift occurs to homologous chromosome.
 External: Shift occurs to non homologous
chromosome.
Reciprocal Translocation:
“Exchange between segments of non homologous
chromosomes or regions of same chromosome”.
Non reciprocal Translocation:
“Movement of a chromosome segment to non homologous
chromosome or region of same chr. without reciprocal
change”.
10

11.  Based on no. of breaks involved:
Simple Translocation:
“It involves one break. Terminal segment of chromosome
integrated at the one end of non homologous chromosome”
Shift Translocation:
“It requires three breaks. Intercalary segment of a chromosome is
integrated within a non homologous chromosomes”
11

12. Ring Chromosome:
“Break occurs in each arm & the 2 sticky ends join
while distal fragments are lost”
Robertsonian Translocation:
“Breakage of 2 acrocentric chr. near centromeres &
fusion of long arms. Short arms are lost”
Other structural abnormalities

14. Numerical Aberrations
“Change in the number of chromosomes is called as
numerical aberration or numerical abnormality”.
Numerical Aberration has two types:
 Aneuploidy (Hyperploidy, Hypoploidy)
 Euploidy (Monoploidy, Diploidy, Polyploidy)
14

15. 15

16. Aneuploidy
• “Change in number of individual chromosomes, but not in
• complete set” e.g., 2n ± 1
• Types of Aneuploidy:
 Hperploidy
• “having chromosomes more than disomic condition (2n)”
 Trisomy(2n+1) :
• “Addition of one chromosome to one pair in diploid set”
16

17. It has two types :
 Simple trisomics – increase in chromosome number in
one pair only (2n+1)
Double trisomics – addition of one chromosomes in two
different pairs (2n+1+1)

 Tetrasomy(2n+2):
“Addition of two chromosomes to one pair or two different
pairs”
Simple tetrasomics – addition of two chromosomes to one
pair(2n+2)
Double tetrasomics – two chromosomes are added each to two
different pairs(2n+2+2)


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18.  Hypoploidy:
“Having chromosomes less than disomic condition(2n)”
Monosomy (2n-1):
“lacking one chromosome from a diploid set”
Nullisomy (2n-2):
“lacking one pair of chromosomes from a diploid set”
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19. Euploidy
“A condition in which one or more full sets of chromosomes are present in
an organism”
Types:
 Monoploidy(n):
“Single basic set of chromosomes”
 Polyploidy:
“More than two multiples of haploid chromosomes sets”
Triploidy (3n) and Tetraploidy (4n).
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20. Abnormal Chromosome number disorders

21. LAWS OF MENDEL

22. 1.MENDEL’S LAW OF DOMINANCE
If your two alleles are different (heterozygous,
e.g. Bb), the trait associated with only one of these will
be visible (dominant) while the other will be hidden
(recessive). E.g. B is dominant, b is recessive.
Sperm
B b
B
b
Eggs
BB Bb
Bb bb

23. CONTD..
• Law of dominance : In a hybrid union, the allele which expresses
itself phenotypically is the dominant allele while the other allele
which fails to express itself phenotypically is the recessive allele.
The hybrid individual shows phenotypically only the dominant
character.
• The law of dominance is often described as Mendel’s first law of
inheritance.

24. 2.MENDEL’S LAW OF SEGREGATION
• A normal (somatic) cell has two variants (alleles) for a
Mendelian trait.
• A gamete (sperm, egg, pollen, ovule) contains one allele,
randomly chosen from the two somatic alleles.
• E.g. if you have one allele for brown eyes (B) and one for blue
eyes (b), somatic cells have Bb and each gamete will carry
one of B or b chosen randomly.
• Law of segregation – the separation of alleles into
separate gametes.
B
b
Sperm
B b
Eggs
BB Bb
Bb bb

25. CONTD..
The law of segregation states:
• Each individual has two factors for each trait
• The factors segregate (separate) during the formation of the gametes
• Each gamete contains only one factor from each pair of factors
• Fertilization gives each new individual two factors for each trait.

26. 3.LAW OF INDEPENDENT ASSORTMENT
• "When a dihybrid (or a polyhybrid ) forms gametes,
(i) each gamete receives one allele from each allelic pair and
(ii) the assortment of the alleles of different traits during the gamete formation is
totally independent of their original combinations in the parents.
• In other words, each allele of any one pair is free to combine with any allele
from each of the remaining pairs during the formation for the gametes
• This is known as the Law of Independent Assortment of characters.
• It is also referred to as Mendel’s third law of heredity.

28. Multiple Allelism
• More than two alternative allelic forms of gene occupy the same loci
in apair of homologous chromosomes are called multiple alleles.
• Determination of a trait by more than two alleles is called multiple
allelism.
• All the variants or alleles of a gene may be originated by mutation of a
single wild type gene.

29. Multiple Alleles in Eye Colourof Drosophila
• Found 14 alleles for eye colour which produce various
shades from white to red.
• Redeye colour is normal(wild type)- dominant toothers.
• Others shades are- wine, coral, blood, cherry, apricot,
eosin, buff, tinged, honey, ecru, pearl, ivory and white.

30. Multiple Allelism In BloodGroups
• Human blood groups wasdiscovered by Dr.KarlLandsteiner in
1900. (father ofblood groups)
• Presenceof two types of proteins in humanblood:-
• Antigens Or Agglutinogen:- glycoprotein present onsurface
of RBCscalled corpuslcesfactor.
• Antibody Or Agglutin:- gamma-globulin present inblood
plasma called plasma factor.

31. Inheritance of ABOBlood Groups
Karl Landsteiner discovered that the ABO blood grouping is
an inherited characteristic and involves multiple allelism.
Genotypes of four types of blood groups:-

32. Phenotype Genotype
O ii
A IAIA, IAi
B IBIB, IBi
Antigen (present Antibody (found
on red blood cells) in the serum)
None anti-A and anti-B
A antigen anti-B
B antigen anti-A
AB IAIB
Both A andB
antigens
None
Different types of blood groups
O- Blood Group is called universal donor- hasno antigen &can donate its blood
to anyperson.
AB- Blood Group is universal recipient- hasno antibody in theirblood plasma.

33. Detection of A, B,and O blood type in humans determined by
multiple allelesand two alleles acting co-dominantly overthird

34. ABO donor recipient combinations. Thetick mark indicates
compatibility in blood transfusionand cross indicatesincompatibility.

35. PossibleBlood Groupsof theChildren of DifferentBloodGroups

36. Significance of Knowledge of Blood Groups
• By knowing of blood groups of parents, blood groups of their children
canbepredicted.
• Helps saving innocent people involved in murder cases and in
identifying the real murderers.
• Helps in safeblood transfusion.
• Usedto settle casesof disputed parentage in mixup casesin hospitals.

37. Rhesus (Rh) Blood GroupSystem
• Rh-Factor:- antigenic protein present on the surface of red blood
cells in humanbeings.
• First discovered by Landsteiner & Weiner(1940) on plasmamembrane
of RBCsof rhesusmonkey.
• Also found in 85% American & 93% of Indians- called Rh-positive
(Rh+).
• Personwith no Rh-factor on the surface of their RBCs-called Rh-negative
(Rh-).
• Rh-factor is controlled by a pair of genes- R & r.(R gene is dominant
and control synthesis ofRh-factor, r-gene cannot synthesize Rh-factor.)

39. Incompatibility during pregnancy

40. Importance of Rh-factor
• Transfusion of Rh+ donor blood into Rh- recipient blood causes clumping of
donor’sRBCs
• It causing blocking of capillaries and death
• No complication occur in first transfusion but subsequent transfusion
causesthis condition
• So, Rh-factor compatibility also considered together with ABO blood
group beforeblood transfusion