1. Principles of Inheritance & Variation

2. Introduction
Existing organisms produces new organism of their own kind.
A lion produces lion and a human beings produce humans ….Why…?
What makes them look similar or dissimilar?

3. Process by which characters pass from one generation to the next is called
Inheritance.
Transmission of characters from one generation to the next is
Heredity.
Though each generation receives characters from the previous generation, yet they are different. These differences are called variations.
Study of inheritance and variation is known as Genetics
Term Genetics was coined by William Bateson in 1906.

4. Theories of heredity
Since beginning scientists have been intrigued by these similarities and differences.
Various theories given since then have been divided into Pre Mendelian, Mendelian and Post Mendelian theories.
Pre mendelian theories have largely been discarded.
These theories assumed that the characters of the parents mixed during transmissions to the offspring.
Therefore, they are called theories of blending inheritance.

5. Gregor J. Mendel Gregor Johann Mendel :
Gregor Johann Mendel( ) is known as the Father of Genetics.
He carried out hybridisation experiments on Garden Pea (Pisum sativum) for seven years ( ) and proposed the laws of inheritance in living organisms.
He published his findings in 1866 in the “Annual of the Natural History society of Brunn.”

6. Mendel’s Experiments Mendel selected Gardens pea because:
Pure varieties of Pea were available.
It showed a number of easily detectable contrasting characters.
Pea flower normally remains closed and undergoes self-pollination.
It allows controlled breeding,i.e., it can undergo both self and cross pollination.
It has short life span

7. Characters Selected by Mendel
He worked with 7 pairs of characters:
Stem height
Flower position
Flower colour
Pod shape
Pod colour
Seed shape
Seed colour

8. Terms
Allele :
Two contrasting expression of a gene which occupy same position (loci) on homologous chromosomes.
Alleles control different traits of same character
Haploid chromosomes
Gene controlling character height of plant
Homologous chromosomes
Gene controlling character height of plant t T T t T
T= Controls tall height (trait1)
Gene controlling height of plant
T= Controls tall height (trait1)
t= Controls dwarf height (trait2)
t= Controls dwarf height (trait 2)
Tall height (trait1)
Dwarf height (trait 2) t
1 gene=2 alleles

9. Dominant Factor or Allele:
Allele which can express itself in both homozygous or heterozygous state., eg., the factor for tallness in hybrid and homozygous states Tt and/or TT.
Recessive Factor or Allele:
Allele which is unable to express its effect in the presence of its contrasting factor in a heterozygous condition is called recessive factor or allele. eg., the factor for dwarfness is able to express in homozygous states tt only.

10. An individual having same alleles (TT, tt). Heterozygous :
Homozygous :
An individual having same alleles (TT, tt). T t T t T
Heterozygous :
An individual having 2 different alleles (Tt).
Genotype :
Genetic constitution of an individual e.g., TT, Tt, tt.
Phenotype :
Externally observable characters which is result if genotype e.g., Tall plant or dwarf plant.
Pure lines/True Breeding :
Individuals always giving same character. (Tall plant always produces tall plant (TT).

11. Monohybrid cross
Study of inheritance of one character at a time
Dihybrid cross
Study of inheritance of two characters at a time
Back cross
It is cross which is performed between hybrid and one of its parents.
Test cross
It is a cross to know whether an individual is homozygous or heterozygous for dominant character. It is made between hybrid and recessive parent.
Reciprocal cross
A pair of crosses between a male of one strain and a female of another, and vice versa.

12. Mendel’s Experimental Procedure
Mendel applied mathematical logic and did statistical analysis of the data. He took large sampling size which gave much credibility to the data collected by him.
1. He selected plants with desired characters. He repeatedly self pollinated them to obtain pure lines, i.e., individuals always giving same character.
Phenotypes
Pure tall plant ×
Pure dwarf plant
Parents
Genotypes TT tt

13. Procedure Contd.
2. These parents were cross pollinated to obtain First filial generation.
Phenotypes
Pure tall plant ×
Pure dwarf plant
Parents tt
Genotypes TT T t
Gametes
Phenotypes
F1 Generation
Tall plant
Genotypes
T t

14. Procedure contd.
F1 generation was self pollinated, to obtain F2 generation.
T t
T t
Phenotypes
F1 Generation
Tall plant ×
Tall plant
Genotypes
Selfing T t T t
Gametes of F1 Hybrids T T t TT
(tall) t Tt
(tall) Tt
(tall) tt
(dwarf)

15. Results of the experiments
F1 plants resembled one parent.
One form of the character, which did not appear in F1 generation, remain unexpressed in it.
In F2 generation both the parental forms of the character are expressed.
The results of reciprocal crosses were similar.
Based on his observations Mendel proposed certain genetic rules which are now called as Principles or laws of inheritance.

16. Principle (Law) of Dominance
(i) Characters are controlled by discreet units called factors.
(ii)Factors occur in pair.
(iii) One factor of a pair of alleles, expresses itself in hybrid. It is called dominant allele and the other allele which is unable to express itself in hybrid is called recessive allele.
2. Flower Position
Axial (A)
Terminal (a)
3. Pod Shape
Full (F)
Constricted (f)
Green (G)
Yellow (g)
Violet/Red (V or R)/ Grey
White (v or r)/White
6. Seed Shape
Round (R)
Wrinkled (r)
Yellow (Y)
Green (y)

17. Law of segregation is universal.
Mendel’s Law of Segregation
Two alleles of a gene controlling a character stay together in the individual.
During gametogenesis, the allelic pair segregate in such a way that each gamete receives only one allele from allelic pair.
Since the gametes possess one allele of each character, they are always pure.
Law of segregation is, therefore, also called the law of purity of gametes.
Law of segregation is universal.

18. law Of Segregation
Mendel crossed Pure tall plant with pure dwarf plant.
Phenotypes
Pure tall plant ×
Pure dwarf plant
Parents tt
Genotypes TT
Gametes T t
Phenotypes
F1 Generation
Tall plant
Genotypes
T t

19. Self Pollination in Hybrids :
F1 generation was self pollinated, to obtain F2 generation.
T t
T t
Phenotypes
F1 Generation
Tall plant ×
Tall plant
Genotypes
Selfing T t T t
Gametes of F1 Hybrids T T t TT
(tall) t Tt
(tall) Tt
(tall)
Analyses of F2 Generation tt
(dwarf)
Phenotypic ratio : 3 : 1 (Tall : Dwarf)
Genotypic ratio : 1 : 2 : 1 (Homozygous Tall : Hetrozygous Tall : Homozygous Dwarf)

20. Results of cross Genotypes TT Tt Tt tt F2 Generation Pure tall Hybrid
dwarf
Phenotypes
F2 Genotypic ratio
1 :
2 : 1
F2 Phenotypic ratio : 1

21. Analysis Genotypes TT Tt Tt tt F2 Generation Pure tall Hybrid tall
dwarf
Phenotypes
F2 Genotypic ratio
1 :
2 : 1
F2 Phenotypic ratio : 1
F2 Genotypic ratio
1/4 :
2/4 :
1/4
F2 Genotypic ratio
1/4 :
1/2 :
1/4
(a+b)2 =a2 +b2+2ab
(1/2 T+1/2t)2 =1/4 TT +1/2Tt+1/4tt

22. Test Cross
When F1 generation is crossed with pure recessive homozygous parent (tt)
Phenotypes
Hybrid tall plant ×
Pure dwarf plant
Parents Tt tt
Genotypes t t T
Gametes T t t Tt
(tall) tt
(dwarf)
Tall : dwarf = 1 : 1 therefore genotype in question is Tt
Test cross for monohybrid cross is always 1: 1

23. Law of Independent Assortment
Yellow Round YYRR
Green Wrinkled yyrr
parents YR yr
Gamete Formation YR
Yy Rr yr
The law states that in a dihybrid cross, inheritance of one character is independent of another character
Yy Rr
Yy Rr
F1 plants
100% Yellow Round
Yy Rr YR YR
YY RR yR yR
Yy Rr
Yy Rr Yr Yr
Yy Rr
yy Rr
Yy Rr yr yr
Yy Rr
Yy Rr
Yy Rr
Yy Rr
F2 plants
yy Rr
Yy rr
yy Rr
9 Yellow Round
3 Green Round
Yy rr
Yy rr
3 Yellow Round
yy rr
1 Green Round

24. 9 3 3 1 Dihybrid phenotypic ratio = 9:3:3:1 Results of cross
Gametes from one hybrid RY Ry rY ry
RRYY
RRYy
RrYY
RrYy RY
Round-yellow
Round-yellow
Round-yellow
Round-yellow
RRYy
RRyy
RrYy
Rryy Ry
Round-yellow
Round-green
Round-yellow
Round-green
Gametes from other hybrid
RrYY
RrYy
rrYY
rrYy rY
Round-yellow
Round-yellow
Wrinkled-yellow
Wrinkled-yellow
RrYy
Rryy
rrYy
rryy ry
Round-yellow
Round-Green
Wrinkled-yellow
Wrinkled-green
Round Yellow
Round Green
Wrinkled Yellow
Wrinkled Green 9 3 3 1
Dihybrid phenotypic ratio = 9:3:3:1

25. Law of Independent Assortment
This law is not universally applicable.
This law holds good if
Genes controlling the character are present on 2 different chromosomes Y y R r
or if Genes controlling the character are present on same chromosome they should be wide apart

26. Mendel selected 7 pairs of contrasting pair of character of Pisum sativum
Genes controlling these 7 pairs of contrasting characters were present on different chromosomes
Note : Mendel was successful in his findings of law of independent assortment as he was lucky to study behavior of genes that were present on two different chromosomes Y y R r
Had the genes were present on same chromosome he would had ended with crossing over and linkage

27. Why Mendel went unrecognized?
However, the great significance of Mendel’s discovery was not appreciated by contemporary biologists, because
(i) His work was ahead of his time,
(ii) He published it in a journal that had limited circulation,
(iii) He was himself not sure of his findings as he failed to get similar results on hawkweed (Hieracium)
(iv) His mathematical approach in working out biological problems was strange for the then scientists, and
(v) Mind of the biologists was pre-occupied with the Darwin’s theory of evolution.

28. Rediscovery of Mendel’s Findings :
In 1900, Hugo De Vries of Netherland, Karl Correns of Germany and Erich von Tshermak of Austria rediscovered Mendel’s findings.
Mendel’s work was got republished by De Vries in Flora in 1901.
A few years later, W. Bateson and others confirmed Mendel’s work and found that the same laws applied to animals also.

29. Exception to Mendelism
Incomplete Dominance (Blended Inheritance)
The expression of the traits of two pure parents as an intermediate condition in the F1 hybrids is known as incomplete dominance.
It is also called blended or intermediate or mosaic inheritance.
It is an exception to Law of dominance.
Example :
Blended inheritance is seen in four o’clock plant (Mirabilis jalapa)

30. Incomplete dominance Phenotypes Parents Genotypes r R R r Gametes
Pure red flower ×
Pure white flower
Parents RR rr
Genotypes r R R r
Gametes
R r
R r
Phenotypes
F1 Generation
Hybrid Pink ×
Hybrid Pink
Genotypes
Selfing R r R r
Gametes of F1 Hybrids R R r RR
(red) r Rr
(pink) Rr
(pink) rr
(White)

31. Results Genotypes RR Rr Rr rr F2 Generation Pure Red Hybrid Pink
White
Phenotypes
F2 Genotypic ratio
1 :
2 : 1
F2 Phenotypic ratio
1 :
2 : 1

32. Analysis F1 hybrid plants with pink flowers are obtained
Neither red nor white is completely dominant, in F1 generation so that both colours appear in the F1 as an intermediate which is pink is obtained
This cross shows Incomplete dominance.
F2 generation includes plants with red, pink and white flowers in the ratio of 1 : 2 : 1.
Thus the genes for red and white colour do not actually mix in the F1 pink hybrids as both the pure characters (red and white) reappear in the F2 plants.

33. Dominance vs Incomplete Dominance
In the F2 generation of the above cross :
(i) Genotypic ratio is the same as Mendelian ratio, being 1 : 2 : 1 (1 R R : 2 R r : 1 r r)
(ii) Phenotypic ratio differs from the Mendelian ratio, being 1 : 2 : 1 (red : pink : white) instead of 3 : 1 (red : white).

34. Codominance :
When the two allele neither show dominant-recessive relationship nor show intermediate condition, but both of them express themselves simultaneously, then this condition is known as codominance.
Such alleles are called codominant alleles.
Characteristics : In codominance, a heterozygote shows a phenotype different from that shown by either of the homozygotes.

35. Example 1 :
Example of codominance is appearance of different types of red blood cells that determine ABO blood grouping in human beings.
These blood groups are controlled by the gene I.
Gene (I) controls the glycoprotein substance, called an antigen, present on the plasma membrane of the red blood cells.
Four phenotypes A, B AB and O are produced by three different alleles IA, IB and i0 of the I gene.

36. Because humans are diploid organisms, each individual possesses any two of the three gene alleles
· Note :i does not produce any sugar.
Alleles IA and IB are completely dominant over i.
· When IA and IB, both express their own types of antigens = blood group AB.
Since there are three different alleles, as many as six different combinations are possible which give only four kinds of phenotype

37. Genotype of offsprings Blood groups of offsprings
ABO Blood Group
Allele from
Parent I
Allele from
Parent II
Genotype of offsprings
Blood groups of offsprings IA IA
IAIA A IA IB
IAIB AB IA i
IA i A IB IA
IBIA AB IB IB
IBIB B IB i
IB i B i i
i i O

38. Multiple Alleles :
More than two alternative forms (alleles) of a gene in a population occupying the same locus on a homologus chromosome = multiple alleles.
Characteristics :
(i) There are more than two alleles of the same gene.
(ii) All multiple alleles occupy the corresponding loci in the homologous chromosomes.
(iii) A gamete has only one allele of the group.
(iv) DIPLOID individual contains only two of the different alleles of a gene, one on each chromosome of the homologous pair

39. (v) Multiple alleles express different alternatives of a single trait.
Multiple alleles conform to the Mendelian pattern of inheritance.
(vi)
Example :
ABO Blood group in man.
Because humans are diploid organisms, each individual possesses any two of the three gene alleles (i.e., IA IA,
IA IB, IA i, IB i, IB IB or i i ).

40. Starch grain synthesis
Pleiotropism
Usually one gene controls one trait but when one gene controls more than one trait, it is case of pleiotropy.
Shape of the seed
Pleiotropy
B gene
Multiple traits
Starch grain synthesis
In Pisum sativum one gene controls both of the characters but shows different inheritance pattern

41. Inheritance of shape of seed
Phenotypes
Round seed ×
Wrinkled seed
Parents BB bb
Genotypes b b B
Gametes B Bb Bb
Phenotypes
F1 Generation
Round seed ×
Round seed
Genotypes
Selfing B b B b
Gametes of F1 Hybrids B B BB
(round) b b Bb
(round) Bb
(round) bb
(wrinkled)

42. Results Analyses of F2 Generation
Phenotypic ratio : 3 : 1 (round : wrinkled )
Genotypic ratio : 1 : 2 : 1 (Homozygous round : Hetrozygous round : Homozygous wrinkled)
Here it shows dominant recessive inheritance pattern)

43. Intermediate starch seed Intermediate starch seed
Inheritance of starch grain synthesis
Phenotypes
Full starch seed ×
Less starch seed
Parents BB bb
Genotypes b B B b
Gametes Bb Bb
Phenotypes
Intermediate starch seed
Intermediate starch seed
F1 Generation ×
Genotypes
Selfing B b B b
Gametes of F1 Hybrids B B BB
(full) b b Bb
(interm) Bb
(interm) bb
(low starch)

44. Results Analyses of F2 Generation
Phenotypic ratio : 1: 2 : 1 (full : intermediate: less)
Genotypic ratio : 1 : 2 : 1 (BB: 2Bb: bb)
Here it shows incomplete dominance inheritance pattern)

45. Sickle cell anaemia
It is an autosomal hereditary disorder which is caused by formation of an abnormal hemoglobin S.
Sickle Cell
Normal Red Blood Cell

46. Mutation in beta chain
Note: a single point mutation has occurred i.e. GAG TO GTG as a result substitution of 6th Amino Acid of beta chain has occurred i.e., Glutamic acid by Valine.

47. Such a mutation effects following traits-:
It contributes to the formation of defective hemoglobin that is much less efficient in carrying oxygen.
RBC’S becomes sickle shaped.
These sickle shaped RBC’S, can not pass through narrow capillaries. Thus, blood circulation and O2 supply are disturbed.
Thus, sickle cell anaemia is an example of Pleiotropy
Individuals heterozygous for the gene are resistant to malaria as Plasmodium is not able to survive in sickle cell RBC

48. Codominance :
Sickle Cell RBC
Normal Red Blood Cell
HbAHbA→Normal individual
HbSHbS→Sickle Cell Anaemic
Sickle Cells
Carriers =Genotype -HbAHbS
as in heterozygous condition both the alleles are able to express themselves
Red Blood
Cells

49. Codominance HbAHbS → Carrier HbAHbS HbAHbS
→ Heterozygous individual (Parents)
HbA
HbS
HbA
HbS
→ Gametes
F1 Generation
HbA
HbS
HbA
HbAHbA
HbAHbS
HbS
HbSHbA
HbSHbS 1 : 2
Healthy
Carrier
Sickle cell anaemic
(Die)

50. Chromosomal Theory of Inheritance.
Watler Sutton and Theodor Boveri independently postulated this theory in 1902
They found that the behaviour of chromosomes was parallel to the behaviour of mendelian factors (genes) and used the chromosome movements to explain Mendel’s Laws.
The similarities are as follows:
Both genes and chromosomes occur in pairs in normal diploid cells.
Both of them segregate during gamete formation and only one member of each pair enters a gamete.
Members of each pair segregate independently of the members of the other pair

51. Linkage and Recombination
T.H. Morgan worked on fruit flies (Drosophila melanogaster).
Drosophila, is used in genetic studies because
Grown on simple synthetic medium in the laboratory.
Complete their life cycle in about two weeks.
Produce a large number flies in the progeny in a single mating.
Drosophila
Female
Drosophila
Male
Male and female flies are morphologically distinct.

52. MORGANS CROSS A
He carried out many dihybrid crosses in Drosophila, with the genes that were sex-linked.
E.g. hybridised yellow-bodied and white-eyed females with brown-bodied and red-eyed males (wild type) (Cross I) and intercrossed their F1 progeny.

53. Cross A
♀ ♂
Parental
TEST CROSS
♀ ♂
F1 generation

54. F2 generation
Parental Type (98.7%)

55. F1 generation ×
Recombinant types (1.3%)

56. Parental Recombinant
Type (98.7%) types (1.3%)
F2 generation

57. CROSS B
E.g. hybridised white-eyed and miniature winged females with red-eyed large winged and males (wild type) (CrossII) and intercrossed their F1 progeny.

58. Cross B
♀ ♂
Parental
TEST CROSS
♀ ♂
F1 generation ×

59. Parental Recombinant
Type (62.8%) types (37.2%)
The strength of linkage between y and w is higher than w and m.

60. Results of the Experiments
F2 ratio deviated very significantly from the 9 : 3 : 3 : 1 ratio (expected when the two genes are independent). Thus, two genes did not segregate independently.
Also, when two genes in a dihybrid cross are located on the same chromosome, the proportion of parental gene combinations in the progeny was much higher than the non-parental.
Thus, if the linkage is stronger between two genes, the frequency of recombination is low, and vice versa.
Sturtevant used the frequency of recombination between the gene pairs on the same chromosomes as a measure of the distance of the genes and mapped their position on the chromosome.

61. SEX DETERMINATION :
In diploid organisms, with separate sexes there are two kinds of chromosomes
Sex Chromosomes/allosomes
Autosomes
The two members of each pair of homologous autosomes are similar in size and shape, but this may not be true of sex chromosomes.

62. (a) Dissimilar Sex Chromosomes :
Dissimilar sex chromosomes exhibit four conditions in animals.
XX-XY. e.g. In mammals, man, and most insects, including fruitfly,
The larger one is known as X chromosome and the smaller one as Y chromosome
Female =XX
Male =XY
Experiments have shown that the genes, which influence sex, lie in the X chromosomes.

63. Homogametic and Heterogametic Organisms.
Organisms having homomorphic sex chromosomes (XX)
produce only one kind of gametes (all with X)=homogametic. XX X X
The organisms with heteromorphic sex chromosomes (XY) forms two kinds of gametes, namely, with X and with Y = heterogametic. XY X Y
Humans female and female fruitfly are examples.

64. SEX DETERMINATION IN HUMANS :
Male ( ♂ )
Female ( ♀ )
Parent X XY XX X Y
Gametes X +
Offsprings XX XY
Female ( ♀ )
Male ( ♂ )

65. Male XO (O means absence of one sex chromosome) and in the Female = XX
SEX DETERMINATION IN OTHER ORGANISIMS :
XX-XO : In certain insects, such as cockroach, and some roundworms, the Y chromosome is missing so that the male has only one sex chromosome.
Male XO (O means absence of one sex chromosome) and in the Female = XX
ZW-ZZ : In many vertebrates (fishes, reptiles, birds) and some insects (butterflies, moths) ZZ=Male and
ZW= Female
(d) ZO-ZZ : In some butterflies the W chromosome is lacking, so that the condition in the Female = ZO and Male =ZZ.)

66. This is called haploid diploid sex determinatiom
HAPLODIPLOIDY IN HONEY BEE
Male ( ♂ )
Female ( ♀ )
Parent X
X=16
XX=32
meiosis
mitosis
=16 X
=16 X
Gametes
Offsprings
=32 XX X
=16
Female ( ♀ )
Male ( ♂ )
This is called haploid diploid sex determinatiom

67. 1. Explain Chromosomal theory of inheritance
2. If the frequency of parental forms is higher than 25% in a dihybrid test-cross. What does that indicate about the two genes involved?
A male fruit fly and female fowl are heterogametic while female fruit fly and male fowl are homogametic . Explain why are they called so?
4. Usually women are blamed for giving birth to girl child . Is it genetically true? Justify
5. Explain sex determination in honey bees

68. MUTATIONS
Mutation is a phenomenon which results in alteration of DNA sequences and consequently results in changes in the genotype and phenotype of an organism
Hugo de Vries
The term “mutation” was coined by Hugo de Vries (1901).
De Vries also proposed mutation theory of evolution in his book “The Mutation Theory” published in 1903.
Hugo de Vries worked on Oenothera lamarckiana or Evening Primorse.

69. Mutations. Mutations. Gene Mutation/ Mendalian mutations
Germinal mutations.
Somatic mutations.
Appear in germ cells and
They are passed on to the offspring.
Appear in body cells (other than germinal)
They generally die with the death of the body.
Mutations.
Gene Mutation/
Mendalian mutations
Chromosomal Mutation

70. Gene mutations produce new alleles.
There are changes in gene structure due to alterations in nucleotide number, type and sequence.
Gene mutations produce new alleles.
They are generally point mutations involving a change in a single base pair.
These are generally studied using Pedigree analysis

71. Pedigree analysis
Pedigree analysis is a kind of genetic analysis in which a trait is traced through several generations of a family to determine how the trait is inherited.
Human inheritance is very complex due to the following special reasons–
Human traits are often not controlled by a single pair of genes as is the case of tallness and dwarfness in peas.
Humans have a mixed ancestry and few, if any, traits are pure. It is, therefore, almost impossible to trace one trait through a family.

72. Then the expression of the trait is shown in the family tree.
Technique of Pedigree Analysis.
Information is gathered about the family’s history for a specific trait.
Then the expression of the trait is shown in the family tree.
It is a convention to represent females by circle and males by squares in a pedigree chart
The symbols are shaded to indicate the trait under study and are left unshaded to show the normal from.
A horizontal line connecting a male and a female indicates mating of parents.
Their children are indicated under vertical lines connected to a horizontal line.
The offspring are numbered with arabic numerals (1, 2, 3 …) in their order of birth from left to right, and a generation is numbered with roman numerals (I, II, III….)

73. Symbols used in the human pedigree analysis
Technique of Pedigree Analysis.
Information is gathered about the family’s history for a specific trait.
Male
Symbols used in the human pedigree analysis
Female
Sex unspecified
Affected individuals
mating
Mating between relatives (consanguineous mating)
Parents above and children below (in order of birth left to right)
Parents with male child affected with disease

74. MENDELIAN DISORDERS
These are gene or point mutations which are transmitted to next generation according to principle of inheritance
They can be dominant or recessive and can be studied by pedigree analysis. They may be autosomal or sex linked.

75. Autosomal Recessive Trait
The genes for autosomal recessive trait are located on the autosomes.
They are expressed only when the offspring is homozygous recessive.
The heterozygous individuals are the carriers of the disease and homozygous dominant are normal.
HbA HbS
HbA HbS I 1 2 3 4 5
HbA –
HbS HbS
HbA –
HbA –
HbS HbS
HbA – II 1 2 3
III
HbS HbS
HbA –
HbA –
E.g. In case of sickle cell anaemia, phenylketouria

76. Autosomal Recessive Trait

77. Phenylketouria
It is an autosomal recessive disorder caused by defective gene associated on 12 chromosome. In this disease individual lack enzyme called phenylalanine hydroxylase which is needed to breakdown phenylalanine to tyrosine in liver.
The genes coding for phenylalanine hydroxylase are defective. Hence phenylalanine accumulates in the body leading to mental retardation.It is also excreted throug urine beacause of it’s poor absorption by kidney.

78. Thalassemia
is a Autosomal linked recessive blood disorder in which synthesis of globin polypeptide of haemoglobin is affected.
Haemoglobin A

79. Thalassemia Sickle cell Anaemia Beta globin gene . Beta globin gene .
Val
His
Leu
Thr
Pro
Glu
Glu
But no Alpha globin chain 1 2 3 4 5 6 7
Val
His
Leu
Thr
Pro
Glu
Glu
QuanTitative defect 1 2 3 4 5 6 7
Sickle cell Anaemia
Beta globin gene .
Val
His
Leu
Thr
Pro
Glu
Glu
Val
His
Leu
Thr
Pro
Val
Glu 1 2 3 4 5 6 7 1 2 3 4 5 6 7
HbA peptide
HbS peptide
= Red blood cells, are sickle shape due to point mutation in beta globin gene.
QuaLitative defect

80. Thalassemia Thalassemia Beta thalassemia Alpha thalassemia
The defect is due to either mutation or deletion in the genes which control synthesis of these globin chains
Absence or reduced synthesis of one of the globin chain results in excess of another
Resulting in the formation of abnormal haemoglobin resulting into anaemia
Thalassemia can be classified according to which chain of hemoglobin molecule is affected
Thalassemia
Beta thalassemia
Alpha thalassemia

81. Alpha thalassemia
Alpha thallasemia occurs when a gene to alpha globin protein are changed (mutated)
2 genes HBA1 & HBA2 code for alpha chain
2 gene loci = 4 alleles

82. Beta thalassemia
Occurs when gene defects affect production of the beta globin protein.
1 gene HBB present on chromosome 11p codes for beta chain
( 1 gene = 2 alleles)

83. Autosomal dominant Trait
Genes for autosomal dominant traits are located on the autosomes.
Trait can appear in the progeny which are heterozygous. Aa aa I 1 2 3 4 II aa aa Aa aa Aa Aa
III 1 2 3 4 5 6 aa Aa aa
E.g. In case of Myotonic dystrophy, cystic fibrosis

84. Sex linked inheritance
Haemophilia
Absence of clotting factors=no coagulation of blood
XX → Normal female
XhX → Carrier female
XhXh → Haemophilic female
XhY → Haemophilic male

85. ALL Haemophilic Daughter carrier
XhY XX X X Xh
XhX
XhX Y XY XY
100% :
100%
Healthy
Male
Haemophilic carrier
female
XhY →Carrier male ====
ALL Haemophilic Daughter carrier

86. XhX → Carrier female ==== 50% haemophilic sonsXY X Y Xh
XhX
XhY X XX XY
50% :
50%
Healthy
Male
Haemophilic male
XhX → Carrier female ==== 50% haemophilic sons
This is case of criss cross inheritance

87. Color blindness XX → Normal female XcX → Carrier female
Sex linked inheritance
Color blindness
Eye fails to distinguish between red and green colors
XX → Normal female
XcX → Carrier female
XcXc → Colorblind female
XcY → Colorblind male

88. XcY XX X X Xc XcX XcX Y XY XY 100% : 100% Healthy Male
Colorblind carrier
female

89. XcX XY This is case of criss cross inheritance X Y Xc XcX XcY X XX XY
50% :
50%
Healthy
Male
Haemophilic male
50% :
50%
Healthy
Female
Carrier
Haemophilic female
This is case of criss cross inheritance

90. Chromosomal Mutation Chromosomal Mutation
These are change in the number and arrangement of genes in the chromosomes.
Chromosomal Mutation
Chromosomal
Abberations
Polyploidy
Aneuploidy
Change in the arrangement of genes
Change in the number

91. Polyploidy
It is the phenomenon of having more than two sets of each chromosomes or genomes.
Diploid
Triploid
Tetraploid
Polyploidy occurs in nature due to the failure of chromosomes to separate at the time of anaphase either due to non disjunction or due to non formation of spindle.

92. Aneuploidy
It is a condition of having few or extra chromosomes than the normal genome number of the species.
The organisms showing aneuploidy are known as aneuploids.
Aneuploidy is of two types.
Loss of Chromosomes
Monosomic (2N – 1).
It is an aneuploid in which one chromosome is devoid of its homologue.
Turner’s syndrome is a viable sex monosomic in human being (44 + X)

93. Turner’s syndrome Turner’s syndrome is caused by XO genotype.
This genotype results from the union of an abnormal O egg with a normal X sperm, or a normal X egg and abnormal O sperm.
The individual has 45 chromosomes (2n – 1)
It is the only known viable monosomy in humans.
Symptoms:
Sterile female with underdeveloped breasts, ovaries,
small uterus, loose skin of the neck,
mostly normal intelligence and short stature,
many male characteristics such as heavy neck muscles and narrow hips.

94. Addition of Chromosomes
Trisomic (2N + 1). It has one chromosomes in triplicate.
Double trisomic has two different chromosomes in triplicate (2 N ).
Trisomic (2N + 1). It has one chromosomes in triplicate.
Down’s syndrome is trisomic in origin where chromosome number 21 is in triplicate.
Klinefelter’s syndrome has an extra X-chromosome.

95. Down’s Syndrome (Mongolism).
The disorder was first reported in 1866 by Langdom Down.
It is caused by the presence of an extra chromosome number 21.
Due to nondisjunction during oogenesis.

96. Symptoms It is characterised by rounded face broad fore-head,
permanently open mouth,
protruding tongue,
projecting lower lip,
short neck,
flat hands and stubby (small) fingers.

97. Klinefelter’s Syndrome
Causes:
Klinefelter’s syndrome is caused by XXY genotype.
This genotype results from the union of a nondisjunction of XX egg and a normal Y sperm or normal X egg and abnormal XY sperm.
The individual has 47 chromosomes (2n + 1).
Symptoms:
Sterile male with small testes,
unusually long legs,
obesity, and sparse body hair,
female characteristics such as breasts.

98. Polygenic inheritance
Quantitative traits refer to phenotypes that are product of two or more genes at different loci
human height
Human skin colours ( controlled by 3 pairs of genes)
Intelligence

101. ASSIGNMENT
When a cross is made between tall plant with yellow seeds (TtYy) and tall plant with green seed (Ttyy), what proportions of phenotype in the offspring could expected to be
(i) Tall and green (ii) Dwarf and green.
A child has blood group O. If the father has blood group A and mother has blood group B, workout the genotype of the parents and the possible genotypes of their offsprings.
In dogs black fur coat is dominat over brown and erect ear is dominat over drooping ear. A dog homozygous for black fur coat and erect ear is crossed with brown fur coat and drooping ears. Workout the dihybrid cross showing the ratio of F2 generation.
A haemophilic man marries a normal homozygous woman. What is the probability that their daughter will be haemophilic.
A human being suffering from Down’s syndrome shows trisomy of 21st chromosome. Mention the cause of this abnormality.
How is the child affected, if it has grown from the zygote formed by an XX egg frtilized by a Y carrying sperm. What do you call this abnormality.
A woman of 47 years delivered an abnormal child with a flattened nasal bridge and mouth partially open with a large protruding tongue. Name the genetic abnormality. What causes the condition.
A pea plant with purple flowers was crossed with white flowers producing 50 plants with only purple flowers . On selfing these plants produced 482 plants with purple flowers and 162 with white flowers. What genetic mechanism accounts for these results.?

102. Happy Learning