Polygenicinheritance.,atavism ,multiple allelism

1. Multiple alleles
Rahana Moideen Koya V.K
1

2. Polygenic
inheritance
2
oWhen one phenotypic character is
controlled by more than one gene,
it is called polygenic inheritance
Kolerenter is known as fatherof
polygenic inheritance
The term was coinedbyMather1941
Quantitative inheritance.
Additive or cumulative influence of
many genes,Measurable traits

3. oIt is also called Quantitative
inheritance
Polygenes are the multiple genes whose
individual effects are smalland almost
equal,but their complementary cumulative
effect governs a quantitative trait.
Environmental influence.
oThe quantity of inheritancedepends
on dominant alleles
oDominant alleles havecumulative
effect each expressing part of trait
3

4. oGene involved in quantitative
inheritance is known as polygenes
oPolygenic inheritance don’t follow
the mendelian ratio
oEg; skin color of man, wheat
kernel colour
4

5. Ratio :
5
owhen 2polygene areconsidered-
1:4:6:4:1
owhen 3polygene areconsidered-
1:6:15:20:15:6:1

6. Skin colour of
man
6
oIt was first studied by Devenport
(1913) in case of Negro-Europeian
intermarriage.
oSkin colour is due to pigment
melanin. More pigment,darker
is the colour.

7. two pair of genes.
oFor Negro :AABB (maximum melanin)
oFor Albino :aabb (minimum melanin)
7

8. o Parents- Negro
(high melanin)
AABB
Albino
(no melanin)
aabb
o Gametes-
o F1--
AaBb
Mullato
8

9. F2-
Gametes- AB Ab aB ab
AB Ab aB ab
AB
AA BB
(Negro)
AA Bb
(Dark)
Aa BB
(Dark)
Aa Bb
(Mullato)
Ab
AA Bb
(Dark)
Aa bb
(Mullato)
Aa Bb
(Mullato)
Aa bb
(Fair)
aB
Aa BB
(Dark)
Aa Bb
(Mullato)
aa BB
(Mullato)
aa Bb
(Fair)
ab
Aa Bb
(Mullato)
Aa bb
(Fair)
aa Bb
(Fair)
aa bb
(Albino)
9

10. 10

11. F2 Ratio- 1:4:6:4:1
11
Number of
Dominant allele
Phenotype Ratio
No of dominant alleles Albino 1/16
One dominantalleles Fair 4/16
Two dominant alleles Mullato 6/16
Three dominant alleles Dark 4/16
Four dominant alleles Negro 1/16

12. 7
6
5
4
3
2
1
0
Negro Dark Mullato Fair Albino
Graphical representation of polygenic inheritance of skin colour in
human 12

13. Negro
6%
13
Dark
25%
Mullato
38%
Fair
25%
Albino
6%
Polygenic inheritance of skin colour in human

14. Wheat kernel
colour
with three genes
F1-
14
F2-

15. ATAVISM or Reversion
In biology, an atavism is a modification of a biological structure whereby
an ancestral trait reappears after having been lost
through evolutionary change in previous generations.
This is a pattern of inheritance in which a genetic trait remains latent
orhidden in several generations and then reappears in a distant
generation. Atavisms can occur in several ways;
one of which is when genes for previously existing phenotypic features are
preserved in DNA, and these become expressed through a mutation that
either knocks out the overriding genes for the new traits or makes the old
traits override the new one. A number of traits can vary as a result of
shortening of the fetal development of a trait (neoteny) or by prolongation
of the same. In such a case, a shift in the time a trait is allowed to develop
before it is fixed can bring forth an ancestral phenotype.[5] Atavisms are
often seen as evidence of evolution. Latin atavus—a great-great-great-
grandfather or, more generally, an ancestor

16. Atavisms have been observed in humans, such as with infants
born with vestigial tails (called a "coccygeal process",
"coccygeal projection", or "caudal appendage. Atavism can
also be seen in humans who possess large teeth, like those of
other primates.In addition, a case of "snake heart", the
presence of "coronary circulation and myocardial architecture
[which resemble] those of the reptilian heart", has also been
reported in medical literature.Atavism has also recently been
induced in modern avian dinosaur (bird) foetuses to express
dormant ancestral non-avian dinosaur features, including
teeth

17. Other examples.
Hind limbs in cetaceans. Extra toes of the modern horse
Reappearance of limbs in limbless vertebrates Re-evolution
of sexuality from parthenogenesis in orbitid mites. Teeth in
chickens.
Reappearance of prothoracic wings in
insects,Reappearance of wings on wingless stick insects[and
earwigs’
.Extra toes in guinea pigs .Reemergence of sexual
reproduction in the flowering plant Hieracium pilosella and
the Crotoniidae family of mites.Webbed feet in
adult axolotls. Human tails (not pseudo-tails
and supernumerary nipples in humans and other primates
Color blindness in humans

19. Multiple Allelism?
More than two alternative allelic forms of
gene occupy the same loci in a pair of
homologous chromosomes in the
population 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.

20. Characteristics
Multiple alleles occupy the same locus with in the
homologous chromosomes. It means only one
member of the series is present in a given
chromosome.
Since only two chromosomes of each type are
present in each diploid cell, only two genes of the
multiple series are found in a cell and also in a
given individual.
The gametes contain only one chromosomeof
each types, therefore, only one allele of the
multiple series in each gamete.

21. Crossing over does not occur in the multiple
alleles.
Multiple alleles control the same
character, but each of them is
characterized by different manifestation.
When any two of the mutant multiple
alleles are crossed, the phenotype is
mutant type and not the wild type.

22. Multiple Allelism In
Blood Groups
Human blood groups was reported by Dr. Karl
Landsteinerin 1900. (father of blood groups)
Presence of two types of proteins in human
blood:-
Antigens Or Agglutinogen:- glycoprotein
present on surface of RBCs called corpuslces
factor.
Antibody Or Agglutinin:- gamma-globulin
present in bloodplasma called plasma factor.

23. Detection of A, B, and O blood type in humans determined by
multiple alleles and two alleles acting co-dominantly over
third

24. ABO donor recipient combinations. The tick mark indicates
compatibility in blood transfusion and cross indicates
incompatibility.

25. Inheritance of ABO Blood Groups
Bernstein discovered that the ABO
blood grouping in an inherited
characteristic and involves multiple
allelism.
Genotypes of four types of blood
groups:-Bernstein discovered that
the ABO blood grouping in an
inherited characteristic and involves
multiple allelism.
Genotypes of four types of bloodgroups:-

26. Possible Blood Groups of the Children of Different
Blood Groups

27. Possible Blood Groups of
Offsprings and Their Parents

28. Significance of Knowledge of Blood
Groups
By knowing of blood groups of parents,
blood
groups of their children can be predicted.
Helps saving innocent people involved in
murder cases and in identifying the real
murderers.
Helps in safe blood transfusion.
Used to settle cases of disputed parentage
in mix up cases in hospitals.

29. Rhesus (Rh)
Blood Group
SystemRh-Factor:- antigenic protein present onthe
surface of red blood cells in human beings.
First discovered by Landsteiner & Weiner(1940)on
plasma membrane of RBCs of rhesus monkey.
Also found in 85% American & 93% ofIndians-
called Rh-positive (Rh+).
Person with no Rh-factor on the surface oftheir
RBCs- called Rh-negative (Rh-).
Rh-factor is controlled by a pair of genes- R & r.(R
gene is dominant and control synthesis of Rh-factor, r-
gene cannot synthesize Rh-factor.)

32. Coat colour in
Rabbit
in rabbits, a series of multiple alleles controls coat color in the
following way:
C+ is dominant to all other alleles and causes full color-Agouti.
The chinchilla phenotype is due to the Cch allele, which is
dominant to all alleles other than C.
The Ch allele-himalayan, dominant only to c (albino), results in
the Himalayan coat color. 296

34. Isoalleles—Stern and Schaeffer 1943-are the alleles whose
phenotypic expression is similar to that of other
independently occurring alleles.So,their effect can be
distinguished from the effect of other genes by special tests.
Two types-normal and mutant.

35. Sex linkage
Morgan1914—Sex linkage is the association or linkage
between the somatic genes and sex determining genes both
are located on the same sex chromosome. Both of them
inherited together as a single block.
Based on the occurance of sex-linkage either in X-
Chromosome or in Y-chromosome,two kinds of sex-linkage
can be recognized.
complete sex-linkage(Morgan1914) and incomplete sex-
linkage.(Darlington1934).
In complete sex linkage ,the genes concerned are
exclusively X-linked or Y-linked ,as the case may be..So,they
are located in the non-homologous segments of X or Y
Chromosome.They are not recombinable by crossing over.

36. In incomplete sex-linkage ,the genes concerned are
located in the homologous segments of both X and Y
Chromosomes. So, they can be exchanged and
recombined by crossing over.
Zig-zag or criss-cross inheritance-Father- to grandson
through daughter transmission-
Ishihara Test--
Shinobu Ishihara (1879-1963), who devised the
procedure and first published a description of it in 1917
Haemophilia-A.Clotting factor-VIII anti-hemophilic factor
(AHF).F8 gene , B-IX factor1952-chistmas factor

37. Colour blindness—Daltanism Ishihara chart,
It is an X-linked recessive trait.Cone
cells.Monochromatia-total
Partial-- Protanopia—red colour blindness,tritanopia-
blue. Duetaranopia-green
Simulation of the normal (above) and
dichromatic (below) perception of red and
green apples

43. Completely Y-linked genes-(holandric
genes)---
Genes located exclusively in no-homologous portion of Y-
Chromosome.Hemizygous genes.
.it is restricted to males.Medeka and guppy fishes-first
reported by Winge.
Hypertrichosis-Hairy pinna and Keratoma dissipatum
(webbed toes due fusion of skin and underlying flesh bet
sec and third toes. )

44. Sex –controlled genes-Sex-conditioned genes or
sex influenced genes
Sex-controlled character, also called Sex-influenced
Character, a genetically controlled feature that may appear
in organisms of both sexes but is expressed to a different
degree in each. Expressed in both sexes.
The character seems to act as a dominant in one sex and a
recessive in the other.Goldschmidt1920-They are autosomal
or sex-linked genes whose dominance and degree of
expression are controlled by sex of the organism. The
intensity and frequency of expression may different in two
sexes .

45. Baldness-Pattern baldness
premature and heritable baldness appearing in their twenties or
early thirties. controlled by autosomal gene.B.
BB-male-bald Bb-male-bald bb—male-non-bald
BB-female-bald -Bb-female-non-bald bb—female-non-bald
Bb bald influence of male hormones.
Pattern baldness,Harelip,gout,more frequent among males.
spina bifida more common females.

46. Sex-limited genes—Morgan—1910—are the genes ,which
are phenotypically expressed only in one sex and repressed in
the other ,although they are present in both sexes.
.Genes whose penetrance is zero in one sex.They are located in
autosomes or in the homologous portion of sex chromosomes.
Devt. Of beard,deep male voice,male musculature,masculine
hair distribution traits expressed in males –influence of male
sex hormones.secondary sexual characters.
Plumage pattern of some breeds of domestic fowls is a
example.Leghorn breed

47. Genotype Male Femalr
HH Hen-feathered Hen-feathered
Hh Hen-feathered Hen-feathered
hh Cock-feathered-ab
female sex
hormone
Hen-feathered-
presence of female
sex hormone.
phenotype
Hen feathering is H ,cock feathering h.The
expression of these alleles is determined by the
allelic(genotypic)combination and the influence
of sex hormones, H.governs hen feathering in the
presence of either male or female sex hormones.
h governs cock feathering in the absence of
female sex hormones and and it governs hen
feathering in the presence of female hormones.

48. Role of Y chromosome in human being
—Active in determining the male sex,since it contains
male promoter genes,
.
The presence of of any no of X chromosomes,in the
absence of Y chromosome produces femaleness,.But if
a single Y chromosome present may develop male
phenotype.
The genes in the X chromosome induce embryonic
differentiation and devt. Of ovary and Y devt.of testis.
Male-determining genes are located on short arm of
the Y chromosome..Deletion of this segment devt, of
female phenotype in XY indl.

49. Devt.of testis in man is governed by a gene-Testis-
determining factorTDF-located in the sex-determining
region of the Y-chromosome..
It regulates the production of a protein .This protein in turn
,regulates the functioning of several accessory genes,which
also govern the devt.of testis.
TDF appears to function as mastergene or regulator gene
,which triggers the expression of several accessory genes to
produce the male sexual characterestics.
In the absence of master gene, only female phenotype will
be expressed. . 236