This document discusses several concepts related to genetics and inheritance patterns: 1. Quantitative or polygenic inheritance involves two or more pairs of non-allelic genes that have a cumulative, additive effect on quantitative traits like height. Environmental factors also influence phenotypic expression. 2. Multiple alleles occupy the same locus and control the same character, with one allele dominant over the others. Examples include eye color in fruit flies and blood groups in humans. 3. Sex determination systems include chromosomal (XX-XY and XX-XO types), genic balance, hormonal influence, and environmental factors determining sex in some species. The chromosomal theory states genes are located on chromosomes that serve as vehicles for gene segregation

2.  If the number of dominant genes
are more, then the degree of
expression of the character will
be more. This kind of inheritance
is termed as Quatitative or
Polygenic Inheritance.

3.  Defined as two or more
different pairs of genes
which are non- allelic,
having cumulative effect and
are responsible for
quatitative characters.

4.  The effects of each contributing gene are
cumulative or additive.
 Each contributing genes produces an equal
effect.
 There is no dominance involved.
 The polygenes have pleiotropic effects, that
is, one gene may modify or suppress more
than one phenotypic trait.
 The environmental conditions have
considerable effect on the phenotypic
expression of polygenes.

5. SkinColour in Men
Height in Man

6.  The presence of melanin pigment in the
skin of the man determines the skin
color. The more pigment the darker is
the skin color. The amount of the
melanin developing individual is
determined by two pair of genes. These
genes are present at two different loci
and each dominant gene is responsible
for the synthesis of fixed amount of
melanin.

7.  In Man, tallness is recessive to
shortness. Individual having a
genotype of more dominant genes
will have shortnesss as their
phenotype.
 The heights of an adult generalyy
range from 140 cm. to 203 cm.

9.  Can be defined as a set of
three, four or more alleles or
allelomorphic genes, which
have arisen as a result of
mutation of a normal gene and
which occupy the same locus in
the homologous chromosomes.

10.  Multiple alleles occupy the same locus within
the homologous chromosomes.
 Since in a diploid cell only two chromosomes
of each type are present, only two genes of the
multiple series are found in a cell and also in
an individual.
 Crossing over does not occur in multiple
alleles.
 Multiple alleles control the same character.
 One is dominant and the rest are recessive or
sometimes they are co-dominant.

11.  Skin Color in Rabbit
 Eye Color in Drosophila
 ABO blood groups in
Human

12.  Why do blood from an individual
cannot always be safely mixed with
that of another?
 This is due to the fact that blood
proteins of one individual differ from
those of others.

13.  The antigens or agglutinogens and
antibodies or agglutinins. The
Antigens A and B are located in the
RBC and the Antibodies a and b in
the Plasma. The antigens are found to
be mucopolysaccharides. The
clumping reaction occurs between
antigen and antibodies and is also
termed as Agglutination.

15. 1. Chromosomal Sex
Determining
Systems
2. Genic Balance System
3. Hormonal System
4. Environmental Sex
Determination

16.  It was given by E.B. Wilson and Steven
(1902)
 The Chromosomal theory of inheritance
states that genes are located on
chromosomes, which serve as the
vehicles of gene segregation in meiosis.
In majority of animals a pair of sex
chromosomes are found. These are
represented by X and Y.

17.  XX-XY Type or Lygaeus Type
 Female homogametic and Male
heterogametic
 Female heterogametic and Male
homogametic
 XX-XO Type or Protenor Type

18.  By: Wilson and Stevens
 The cell of the male and the females
have the same number of
chromosomes but the females have
two X chromosomes and the males
have one X and the small Y
chromosomes.

19.  Female Homogametic  Female Heterogametic
and Male and Male
Heterogametic Heterogametic
 Females are  In fowls, other birds
homogametic sex with and some fishes, some
XX chromosomes. They amphibians, moths and
produce eggs of same butterflies, the female
type, carrying on ly X sex is heterogametic
chromosomes. On the with X and Y
other hand, males are chromosomes. XX-XY
heterogametic with XY system, are labelled as
chromosomes. Z and W.

20.  In Squash Bug it was observed that males
have 21 chromosomes, but females have 22
chromosomes. Thus all the eggs of the
same type carrying X chromosomes while
the Sperms of Two types; 50% with 11
chromosomes and 50% with 10
chromosomes. Fertilization of an egg by
the sperm carrying 11chromosomes result
in female, while fertilized egg by sperm
with ten chromosomes produces male.

21.  According to this theory, every
individual whether male or female,
possesses in its genotype genes for both
male and female characteristics.
Depending upon the number of genes
of a particular sex the organism’s sex
will be determined. If there is excess of
female determining genes, female
develops; if the male determining genes
are in excess, a male is formed.

22.  In higher vertebrates, the embryo develops
some characters of the opposite sex together
with the characters of its own sex
chromosome. This is due to the hormones
secreted by the reproductive organs of the
animal.
 A large number of cases are known where sex
is modified due to hormones secreted from
sex organs. Some examples are:
 Sex reversal
 Freemartin

23.  This case of sex reversal was explained by
assuming that when the ovary is destriyed
on removal, the ovarian hormones were
stopped. In the place of ovary, the
rudimentary gonad (this is a non-
functional gonad in birds) started
functioning as testis. The male hormones
were produced and resulted in the
appearance of the male secondary sexual
characters and the formation of sperm.

24.  Freemartin is the effect of the
hormones of the male sex on the
female.
 Studies show:
 F.R. Lilies found that in cattles, where twin
calves of opposites sex (one male and the
other female) are born, the male is normal
but the female is sterile with many male
characteristics. Such sterile females are
known as Freemartin.

25.  In number of organisms, sex is determined
fully or partly by environmental factors.
 Environmental factors are also important in
determining sex in many reptiles. Although
most snakes and lizards have sex
chromosomes, in many turtles, crocodiles and
alligators, during embryonic development
determines sex.
 Example:
 In turtles, warm temperature produces females during
certain times of the year, whereas cool temperature
produces males.

26. Prepared To: Miss Sheryllene J. Lat
Bsed III-B Day